Carrier Selective Contacts Based on Dielectric/Metal/Dielectric Structures
Polytechnic University of Catalonia, Spain
Transition Metal Oxides (TMOs) have been successfully used as a selective contacts in Heterojunction (HIT) crystalline silicon solar cells. TMOs acts as an effective Hole Transport Layer (HTL), allowing electron transport and blocking hole carrier transport. Efficiencies as high as 22.5% were reported in n-type crystalline silicon using MoO3 as a HTL.
Indium-Tin Oxide (ITO) is the standard material used as a Transparent Conductive layer (TCO) on top of the TMOs layer to improved carrier collection. Although ITO presents excellent optical and electrical properties, its manufacturing requires scarce rare elements and expensive technological processes, limiting their compatibility with large area, low cost solar cells. Therefore, alternative transparent electrodes with excellent opto-electrical performance are demanded.
Recently, DMD (dielectric-metal-dielectric) structures has emerged as a prominent candidate to substitute the ITO electrode in organic based devices. Different dielectrics and metals are currently be tested as the best options to fabricate DMD structures. Interestingly, some of the best DMD structures, in terms of their opto-electrical properties, were fabricated using TMOs as the dielectric layer. This fact opens the possibility to use TMO-based DMD structures in crystalline silicon solar cells, fulfilling two objectives. On one side, the use of TMOs layer in contact with the crystalline silicon will act as a selective contact, and, on the other hand, the DMD structure will serve as a replacement of the ITO layer.
In this work, we study the optical and electrical properties of several a dielectric-metal-dielectric (DMD) structures based on TMOs. In particular, MoO3/Ag/MoO3, V2O5/Ag/V2O5 and WO3/Ag/WO3 configurations deposited by thermal evaporation on glass substrates were optimized in terms of optical transmittance and electrical conductivity.
Finally, crystalline silicon HIT solar cells including optimized DMD structures were fabricated in order to test the properties of the DMD structure in a real solar cell device.
Characteristics of Vanadium Oxide Thin Films Grown by Atomic Layer Deposition Using VCl4 and H2O as Precursors
Department of Applied Physics, National Pingtung University, Taiwan
In this work, vanadium oxide (VOx) films were grown on n-type Si (100) substrates at temperatures of 200 – 500 oC by atomic layer deposition (ALD) with 1000 reaction cycles. VCl4 and H2O were used as precursors to grow VOx films, and Ar was used as the purge gas of ALD. The reservoirs of VCl4 and H2O precursors were kept at the temperatures of 30 and 25 oC, while the injection volumes of VCl4 and H2O vapors for each injection pulse determined by the reservoir temperature and vapor injection time were 0.288 and 0.296 cc/pulse, respectively. The flow rate of Ar gas was 5 sccm, as controlled by mass flow controller (MFC). An 8-step ALD reaction cycle was used to grow VOx films. The time used for each step in an ALD cycle was 0.1, 1, 1, 1, 0.5, 1, 1, and 1 s for VCl4 vapor injection, pump-down, Ar purge, pump-down, H2O vapor injection, pump-down, Ar purge, and pump-down, respectively. The crystalline structures of films were determined by X-ray diffractometer (XRD). The film surface morphologies and roughness were analyzed by scanning electron microscope (SEM) and scanning probe microscope (SPM). The element composition of VOx films were analyzed by X-ray photoelectron spectroscope (XPS). In addition, the relationship between the characteristics and growth conditions of VOx films were carefully discussed.
Chemical Bath Deposited p-CuO/n-Si and p-CuO/n-ZnO Nanowires Heterojunction Solar Cells: A Comparative Study for Photovoltaic Performance
1University of Calcutta, India; 2Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore
The p-CuO/n-Si and p-CuO/n-ZnO nanowire heterojunction diodes are fabricated by employing chemical bath deposition technique on n-Si substrate. Comparative study of the p-CuO/n-Si diode is performed in reference to the p-CuO/n-ZnO nanowire diode in terms of film and nanowire morphology, chemical composition, crystallite structures, optical and photovoltaic performance. Optical parameters of the CuO film and ZnO nanowires including refractive index, absorption coefficient and band gaps are extracted from the respective spectroscopic ellipsometric results. The electrical and photovoltaic measurements are performed for extracting the junction rectification properties at dark condition and power conversion efficiency is determined by measuring the relevant short circuit current and open circuit voltage at white light illumination. The values of energy conversion efficiency are measured to be 0.63% and 7.9%, respectively, for the p-CuO/n-Si and p-CuO/n-ZnO heterojunction diodes, for an input incident power of 0.037 mW/cm2. The study suggests a technological route for developing high quality, low cost p-CuO/n-ZnO metal-oxide heterojunctions for photovoltaic and solar cell applications by employing the chemical bath deposition method.
Controlled Growth of Cu2O Thin Films by Electrodeposition Approach
1Hamad Bin Khalifa University, Qatar; 2Qatar University, Qatar
Thin films of Cu2O comprised of wavelike surface characteristic of compact nanoparticles were synthesized using a facile and cost-effective electrodeposition approach. The Cu2O films were synthesized by electrochemically reducing the copper precursors in presence of complexing agents under pH 11 and chronoamperometrically at a fixed potential. The distinct surface morphologies with well-aligned crystal orientation were obtained through the controlled electrodeposition parameters. The high resolution AFM combined with the peak force AFM images mapped the nanomechanical and chemical properties of the Cu2O nanostructured films. The structural, optical, and compositional analyses of the as-deposited thin films showed bulk Cu2O material with preferred texture of (111) and trace amounts of CuO on the top layers as a result of the surface oxidation during exposition to atmospheric conditions. The electrodeposition approach could proceed non-intermittently under ambient conditions, and provides a facile and economic way of depositing films of Cu2O with wavelike characteristics. The fluorescence lifetime was found be very short in the range of 0.8-1.3 ns for the Cu2O films. The Mott-Schottky measurement exhibited p-type conductivity and carrier density was observed to be ~2x1018. The observed fluorescence lifetimes, and carrier densities could help implementing the Cu2O films as an efficient hole-conducting, and photoelectrode materials in solar cells and water splitting devices. The electrodeposited Cu2O thin films are being applied as hole conducting material in solar cells.
Cu2ZnSnS4 (CZTS) Thin Films Prepared by RF Sputtering of Non-stochiometric Quaternary CZTS Target
1Nanyang Technological University, Singapore; 2Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore
Cu2ZnSnS4 (CZTS) is a promising absorber material for low cost thin film solar cells. Single junction photovoltaic devices based on CZTS have potential to reach power conversion efficiency of 28% according to the Shockley-Queisser limit. Widely used method to fabricate CZTS thin films comprises of two stages: deposition of precursors stack and subsequent sulfurization of a precursors[2,3]. Sputtering of a single quaternary target is an alternative method to fabricate CZTS thin films. This is a simple and highly reproducible approach which enables to obtain more uniform thin films and potentially reduce sulfurization time.
Here we will present properties of CZTS thin films deposited by the single target sputtering method on a glass and W-coated glass substrates. X-ray diffraction, Raman spectroscopy, Scanning electron microscopy, Energy dispersive spectroscopy are used to characterize the composition and structure of the as-deposited films. Surface composition is studied by X-ray photoelectron spectroscopy. Sulfur-free rapid thermal annealing at 550°C for 5 min improves the crystal quality of the film.
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 T. Fukano, S. Tajima, T. Ito, Appl. Phys. Express 6, 062301 (2013).
 A. Emrani, P. Vasekar, C.R. Westgate, Solar Energy 98, 335-340 (2013).
CuSbS2 Thin Films by Chemical Solution Methods and Post-Deposition Annealing
Centro de Investigación en Materiales Avanzados, S.C., Unidad Monterrey, Mexico
CuSbS2 has been currently studied as an alternative absorbed material in thin film photovoltaic applications. It shows a p-type conductivity, a direct band around 1.3 - 1.5 eV, and a strong light absorption (α > 104 cm-1). In addition, the availability and low cost of its constituent elements make it a suitable alternative to replace the CuInS2. In this work is proposed a chemical method of copper incorporation into amorphous antimony sulfide (a-Sb2S3) thin films via cation exchange, with the goal of obtaining Sb2S3/Cu2S thin films as a precursor structure to conversion into CuSbS2 through annealing. The a-Sb2S3 films were obtained by chemical baths containing SbCl3, and Na2S2O3 solutions at 10 °C for 1 h. The cationic exchange was carried out in a Cu+ solution at room temperature (25 °C). ICP analysis and cross section SEM images confirm the cationic exchange in the solution and the development of a bilayer as a first step for the ternary material formation. After annealing the deposited bilayer at 350 °C for 1 h in a vacuum oven (4 x 10-6 Torr), polycrystalline CuSbS2 thin films were successfully obtained, without the presence of oxides, copper and antimony sulfides, or other copper-antimony-sulfide phases evidenced by X-ray diffraction. The optical properties shown a direct band gap of 1.5 eV and an absorption coefficient of 105 cm-1 (hv > 1.5 eV), values that match with the requirements for the photovoltaic materials. These and other result from characterization techniques demonstrate the viability to obtain CuSbS2 films by the simple chemical methods presented here, with promising properties to be used as absorbed layer in photovoltaic cells.
Deposition of Bulk MoS2 Films by Electrodeposition Approach for Photovoltaic Applications
1Hamad Bin Khalifa University, Qatar; 2Qatar University, Qatar
Transition metal dichalcogenides, especially molybdenum disulfide (MoS2) has drawn much attention as a light absorbing material for photovoltaic application due to its high carrier mobility of ~200 cm2V-1S-1, direct and indirect band gap energies of ~1.8 eV, and ~1.3 eV, respectively, and excellent light absorption characteristics. These intriguing physical properties of the layered MoS2 films crucially contributed to obtain high efficiency devices of water spliting, energy storage, field-effect transistor, and gas sensors. In our work, bulk MoS2 thin films were deposited onto conducting FTO substrates by utilizing a non-vacuum, environmentally friendly, cost-effective, and earth abundant aqueous solution-based facile electrodeposition approach. Moreover, layered structure of the MoS2 film is believed to suppress surface dangling bonds and consequently recombination sites of photogenerated charge carriers in solar cells. The as-deposited MoS2 films were revealed to be amorphous in nature, which were subsequently post-treated in a sulfurization chamber under inert atmosphere for grain growth as well as for maintaining stoichiometry of the electrodeposited films. While the MoS2 films post-treated under argon atmosphere in a quartz tube furnace showed traces of MoO3, the compositional analysis of the sulfurized MoS2 films by X-ray Photoelectron Spectroscopy revealed the presence of phase pure MoS2 films. The AFM topographic images of MoS2 films showed its compact and bulk films. In addition, UV-Vis, Time-resolved Photoluminescence, and Electrochemical Impedance spectroscopy techniques were utilized to characterize the post-treated crystalline MoS2 films for determine electronic properties. The post-treated MoS2 films resulted unity light absorption due to its thick and bulk nature and was utilized as panchromatic light absorber in Schottky junction solar cells. Optimized stack layers of the MoS2-based solar cells and device performances will be presented.
Direct Comparison of Sn-Assisted Annealing in Sulfur Vapor and H2S on Non-toxic Solution Processed Earth Abundant monoclinic-Cu2SnS3 Thin-films and Their Photovoltaic applications
Nanyang Technical University, Singapore
Cu2SnS3 (CTS) is a promising non-toxic and earth abundant photovoltaic absorber, which is chemically simpler compared to the widely studied Cu2ZnSn(SSe)4. However, CTS currently have relatively low efficiency and suffers poor reproducibility, often due to suboptimal material quality which leads to degraded optoelectronic properties. To address these issues, here we study the effect of annealing in with and without Sn-assisted sulfur vapor and H2S environment on non-toxic solution spin-coated CTS thin films. The annealed CTS films were characterized by X-ray diffraction, Raman spectroscopy, UV–vis spectroscopy, and scanning electron microscopy techniques. It is observed that annealed CTS films show improved structural quality and optoelectronic properties, when introduced Sn during the sulfurization process. These improvements also lead to more reproducible CTS PV devices, with performance currently limited by a large cliff-type interface band offset with CdS contact.
Effect of Post-annealing Treatment on Cation-substituted CZTS
1Energy Research Institute @NTU (ERI@N), Nanyang Technological University, Singapore; 2Physics Department, South University of Science and Technology of China, China; 3School of Materials Science and Engineering, Nanyang Technological University, Singapore
Copper zinc tin sulphide (CZTS) is a promising material for use in thin-film photovoltaics, due to its earth-abundant constituents, solution processability, and structural and electronic similarities to copper indium gallium selenide (CIGS). The major concern for CZTS-based solar cells is the low VOC as compared to the theoretical Shockley-Queisser limit. Here, we report the use of a combination of ITO electrode, cation substitution, and postannealing treatments to increase the VOC of CZTS-based solar cells. We also find that the use ITO instead of the commonly employed AZO as the electrode is essential for the post-annealing treatment to be beneficial. The efficiency of CZTS increases from ~4% to ~7%; similar beneficial effects are obtained for other cation substituted kesterites, to a varying extent. The reasons for this variation, and those for the overall increase in the device performance are discussed.
Effects of Selenization Time and Potassium Treatment on Device Performance of Solution Processed CZTSSe Solar Cells
1Nanyang Technological University, Singapore; 2South University of Science and Technology of China, China
Due to the great potential for large-scale and low-cost production in photovoltaic industry, solution processed kesterite Cu2ZnSn(S,Se)4 (CZTSSe) is one of the most promising candidates for future PV application. Composed of relatively low toxic and earth abundant elements, it could be used to avoid the limitation of elemental scarcity and relieve the environmental issues. However, the device performance of CZTSSe solar cells is still subjected to low open circuit voltage (Voc) and low fill factor (FF), which are mainly caused by deep defects and high carrier recombination at the interface and grain boundaries (GBs). In this work, the influence of different selenization times t (t = 10, 20, 30, and 40 min) has been investigated for undoped and K-doped CZTSSe devices, and we demonstrate that both the selenization time and potassium treatment could influence the electrical properties and defect physics of CZTSSe device, thus affecting the solar cell performance. From C-V and C-f measurement, we conclude that K treatment with non-ideal selenization time (10 and 40 min) is found to induce deep level states, higher series resistance and lower shunt resistance, thus deteriorating Jsc and FF; while K treatment with ideal selenization time (20 and 30 min) is shown to improve Jsc and Voc. Based on our study, the combined effects of both selenization time and K doping treatment on the electrical properties and device performance of CZTSSe solar cells has been elucidated.
Enhancement of Charge Separation in (ZnSe)0.85(CuIn0.7Ga0.3Se2)0.15 Photocathodes for Efficient Hydrogen Production from Water under Sunlight
1School of Engineering, The University of Tokyo, Japan; 2Japan Science and Technology Agency, Precursory Research for Embryonic Science and Technology (JST PRESTO), Japan
Photoelectrochemical (PEC) water splitting using combination of a photocathode and photoanode is an attractive approach to efficient and simple production of hydrogen from water utilizing sunlight without fossil resources. Recently, it has been reported that a (ZnSe)0.85(CuIn0.7Ga0.3Se2 (CIGS))0.15 thin film is a promising candidate for the photocathode material because it shows a cathodic photocurrent at a wide range of potentials up to 0.9 VRHE under simulated sunlight. Moreover, the long absorption edge of 850~900 nm is a desirable property for efficient solar-to-hydrogen conversion. However, there was a large gap between the theoretically maximum photocurrent value of 34 mA cm-2 and the experimentally observed value of 7 mA cm-2. Hence, further improvement in the photocurrent has been required to realize efficient PEC water splitting.
In this study, we investigated effect of composition gradient of In and Ga in depth on the PEC property. A (ZnSe)0.85(CIGS)0.15 with a bilayer structure, which has an In-rich phase and Ga-rich phase on the surface and substrate sides, respectively, was fabricated by modifying the process of film deposition. Cross-sectional electron-beam-induced current (EBIC) mapping was employed to evaluate the charge separation effect in the photocathode. As a result, the EBIC analysis clarified that the bilayer sample showed more uniform distribution of built-in potential in the vicinity of the photocathode surface than the case of a monolayer sample. Consequently, the photocurrent value at 0 VRHE increased to almost twice and reached 12 mA cm-2 under simulated sunlight. By using the modified (ZnSe)0.85(CIGS)0.15 photocathode and a BiVO4 photoanode, a PEC cell demonstrated overall water splitting reaction without application of external bias voltage. In the presentation, we are going to discuss the results of the EBIC analysis and overall water splitting over the PEC cell in detail.
Enhancement of Electronic Functionalities in Fe2O3 via Hydrogen Doping
1NUS Graduate School of Integrative Sciences and Engineering, National University of Singapore, Singapore; 2NUS Nanoscience and Nanotechnology Initiative - NanoCore, National University of Singapore, Singapore; 3Material Sciences and Engineering, National University of Singapore, Singapore; 4Singapore Synchrotron Light Source, National University of Singapore, Singapore
Hematite (α-Fe2O3), one of the most stable oxides of iron, is a photo-anode material candidate. It has the ability to harness solar energy and convert it into chemical energy by driving water hydrolysis. This is possible because Fe2O3 has an optical bandgap (~2.1eV) which straddles the water oxidation and reduction potentials. Furthermore, Fe2O3 is chemically resistant, non-toxic and cheaply available, making it a very promising material to manufacture hydrogen in an environmentally friendly way. Unfortunately, the major drawbacks of Fe2O3 are that it has poor electrical conductivity and carrier dynamics, yielding low solar-to-hydrogen conversion.
In this study, we use catalytic hydrogenation to dope electrons in Fe2O3 to enhance its electrical performance. Hydrogen in its nascent atomic state has the ability to bond with Oxygen atoms causing a net donation of electrons into the host Fe2O3 lattice. This increases the electronic conductivity of the material by 3-4 orders of magnitude. Interestingly the optical band-gap of Fe2O3 remains unaffected. Hence hydrogen doping provides a surgical strategy to enhance the electronic functionality of Fe2O3. The novel phase hydrogenated phase of Fe2O3 is characterized by X-Ray Diffraction, Raman Spectroscopy, UV-Vis Spectroscopy, Optical Microscopy and Elastic Recoil Detection Analysis. We also present the effect of hydrogen doping on the photo-electro-chemical performance of Fe2O3 photoanodes.
Exploring the Optical Properties of Earth-Abundant Chalcogenide Absorbers
1Centre for Materials Science and Nanotechnology, University of Oslo, Norway; 2Department of Materials Science and Engineering, KTH Royal Institute of Technology, Sweden; 3Department of Physics, University of Oslo, Norway
Emerging earth-abundant chalcogenide materials are explored to benefit from the high absorptivity in combination with low effective mass of the minority carriers. In the present study, we explore and compare various emerging compounds, like for example CuSb(Se,Te)2, Cu3Bi(S,Se)3, Cu2S, Sb2S3, Bi2S3, and Cu2XSnS4 (X = transition metal atoms). We calculate the electronic and optical properties using a hybrid functional approach within the density functional theory. By modeling the quantum efficiency and the maximum conversion efficiency for different thicknesses of the absorber materials, the optimal device efficiency is estimated. Based on the theoretical analyses, we describe the advantages and disadvantages of the different compounds. The results help to understand fundamental physics of the emerging earth-abundant chalcogenides in order to tailor-make materials and optimize the solar cell devices.
 R. Chen and C. Persson, J. Appl. Phys. 112, 103708 (2012).
 S. G. Choi, et al., Appl. Phys. Lett. 101, 261903 (2012).
 M. Kumar and C. Persson, Appl. Phys. Lett. 102, 062109 (2013).
Functionalized Mesoporous Carbon Nitrides for Dye-sensitized Solar Cell Application
University of South Australia, Australia
Mesoporous carbon nitrides (MCN) have been actively explored in diverse applications such as photocatalytic water splitting, energy storage and conversion based devices. However, the reports on the energy harvesting system based on MCN are quite limited. Herein, we demonstrate the first-ever report on the use of MCN as a novel photoanodic material in the proof of concept solid device architecture in dye-sensitized solar cell (DSSC) with the aim of replacing existing metal oxide based photoanodes in DSSC which suffer from poor stability and light absorption. By designing a novel metal free, semiconducting, and functionalized MCN as a photoanode, we envisage that the newly fabricated materials can provide better advantages by manipulating energy-level band gap (< 2.7 eV) and their positions to improve the light absorption capability from the visible and near infrared portion of the solar spectrum, electron generation, transport and minimization of electron-hole recombination. The functionalized MCN synthesized by using 5-Amino-1H-tetrazole as the carbon nitride precursor, annealed at various temperature, i.e. 400, 500, and 600 °C, and 2D & 3D mesoporous silica as nano-hard templates with different pore diameters and morphologies seem to enhance specific surface areas and pore diameters. This helps to enhance the adsorption of dye molecules on the MCN photoanode. Furthermore, the role of precursors, textual parameters and morphology on the electrochemical, optical and electronic properties of the new MCN are assessed and correlated with corresponding enhancements in the photovoltaic performance. The MCN proposed here with different functional groups and nitrogen contents compared to non-porous carbon nitrides exhibit a promising power conversion efficiency of over ~ 0.8% possibly opening up a new class of photoanodes in DSSC. It is believed that the efficiency can be further elevated up to over ~ 2 to 3% by the careful optimization of the processing conditions through tuning film morphology and device stack.
Highly Stable Aluminum Incorporated Cupric Oxide for Visible Light Driven Electrochemical Water Splitting
1National University of Singapore, Singapore; 2Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore
Aluminum incorporated cupric oxide (CuO:Al) thin film was prepared by co-sputtering the CuO and Al onto the fluorine-doped tin oxide (FTO) coated glass substrate and incorporated into a photoelectrochemical (PEC) cell as a photocathode. It is shown that incorporation of Al into CuO film significantly improves the photo-corrosion stability compared to the CuO film. Incorporation of Al into CuO film also improves the hydrogen evaluation rate. Strutural proerty and surface morphology have been investigated using XRD and SEM analysis. Furthermore, we have also investigated stability of the Al incorporated CuO photocathode through structural and chemical analysis.
Improved Performance in Quantum Dot Solar Cells with Inserting ZnSe Layer
1KLE’s S.K.Arts & H.S.K. Science Institute, India; 2Anekant Education Society’s, Jaysingpur College, India; 3Karnatak University, India
Solution processing is a promising route for the realization of low-cost, large-area, flexible and lightweight photovoltaic devices with short energy payback time and high specific power. However, solar cells based on solution-processed organic, inorganic and hybrid materials reported thus far generally suffer from poor air stability, require an inert-atmosphere processing environment or necessitate high-temperature processing, all of which increase manufacturing complexities and costs. Simultaneously fulfilling the goals of high effciency, low-temperature fabrication conditions and good atmospheric stability remains a major technical challenge, which may be addressed, as we demonstrate here, successful design and fabrication of QDSCs with a improved efficiency based on CdS/CdSe QDs with two ZnSe layers inserted at the interfaces between QDs and TiO2 and electrolyte. The effects of two ZnSe layers on the performance of the QDSCs were systematically investigated. The results indicated that the inner ZnSe buffer layer located between QDs and TiO2 serve as a seed layer to enhance the subsequent deposition of CdS/CdSe QDs, leading to higher loading amount and covering ratio of QDs on the TiO2 photoanode. The outer ZnSe layer located between QDs and electrolyte behave as an effective passivation layer which not only reduces the surface charge recombination, but also enhances the light harvesting.
Improvement of CZTS Device Performance by Ag Substitution and Alkali Metal Doping
Nanyang Technological University, Singapore
Copper zinc tin sulphide (CZTS) based solar cells have received much attention due to their interesting optoelectronic properties and low cost constituents. The bottleneck of these devices is the open circuit voltage (VOC) deficit from their theoretically expected value which are mainly attributed to antisite defects. The VOC of these devices can be improved by substituting few percentages of the copper atoms with bigger atoms like Ag which can reduce antisite defect formation. However, Ag incorporation reduces the hole concentration and with higher content of Ag, CZTS becomes n-type. Generally, doping of alkali metals in CZTS system help to improve the carrier concentration and grain growth. In this work, we report that alkali metal treatment on Ag-CZTS results in device with a power conversion efficiency (PCE) of 7.72% while CZTS based system has the PCE of 6.84 %. A systematic study on the composition and ratio of Ag with the alkali metal is being carried out. The role of alkali metal doping on the improvement of device performance will be discussed.
In Situ Plasmonic Nanoparticle Doped Electrospun Mesoporous Titania Nanofibers: Efficient Solar Light Harvesting Materials
CSIR-Central Glass and Ceramic Research Institute, India
Titania (TiO2) shows great potential in environmental remediation, water splitting and solar energy conversion under artificial or natural solar light. However, use of TiO2 under visible or solar light gets restricted because of its relatively wide band gap. Accordingly, modification of the band structure is required to attain visible light activity of TiO2. Strategies including doping of plasmonic metal nanoparticles (NPs) within TiO2 framework with morphology tuning are often considered as effective routes to improve the solar energy harvesting. Keeping this in mind, we have fabricated plasmonic electrospun TiO2 nanofibers with quasi-ordered mesopores by in situ incorporation of metal NPs (Au, Ag and Cu) and their alloys. The doped mesoporous anatase TiO2 nanofibers were thoroughly characterized by HRTEM, hi-resolution XRD and diffused reflectance absorption spectrophotometry. Furthermore, the solar light photoactivity of these nanofibers was systematically evaluated with respect to their plasmonic absorption by monitoring the photodecomposition of organic dye pollutants and through the fabrication of dye sensitized solar cell under 1.5G solar simulator (100 mW cm–2). The improved photoactivity of these plasmonic mesoporous fibers was observed due to the embedment of plasmonic feature possessing NPs within the 1D mesoporous fibrous morphology that facilitated rapid electron transfer as well as easy diffusion of reactant.
Investigation on the Viability of Various Earth Abundant Cu2MSn(S,Se)4 as Absorber Layer in Thin Film Solar Cell
1Nanyang Technological University, Singapore; 2Energy Research Institute at NTU (ERI@N), Nanyang Technological University, Singapore
Investigation on the crystal structure and optical properties of Cu2(Metal)Sn(S,Se)4 layers were conducted to study their viability as cheap and environmentally-safe alternative absorber in thin film solar cell. Substitution of zinc with other bivalent metal from Cu2ZnSn(S,Se)4 (CZTSSe) is an approach to eliminate Cu/Zn antisite defects problem in CZTSSe. Cu/Zn antisite defects is common in CZTSSe due to Zinc’s role which is overlapping with Copper. Thus, in this study Cu2M(Metal)SnS4 thin films were fabricated on Molybdenum-coated glass by chemical spray pyrolysis (CSP) technique with variation of Metal (Mg, Mn and Ni). The precursor used was a mixture of metal ion Chlorides and Thiourea with fixed ratio. The pyrolysis was done in atmospheric condition with hotplate temperature 450oC. This was followed by a selenization process with temperature 520oC for 12 minutes. X-ray Diffraction (XRD), Raman Spectroscopy and ultraviolet-visible light spectroscopy (UV-Vis) were done to investigate the crystal structure and band gap of the compounds and act as premises to select the compound to focus on. Cu2MnSn(S,Se)4 is promising owing to its purity and low band gap. Following that, an optimization was done on selenization temperature. Crystal structure, band gap and J-V Curve characterizations were carried out to samples with three different temperatures, 460oC, 500oC and 540oC. The result shows a better crystallinity, lower band gap and higher efficiency for higher temperature. This is also being shown as the highest performance cell with efficiency of 0.9%. Further optimization especially on the buffer layer should be done in the future to improve the performance.
Perylene-Diimide Based Organic Small Molecule Acceptors for Efficient Fullerene-Free Organic Solar Cells
Kookmin University, South Korea
Solar flux is unlimited and environmentally friendly energy resource evaluated as a potential primary energy source for the future. Commercialized silicon solar cells satisfy the high efficiencies but encounter the practical problems because they need costly processes to make, require large space to install and are heavy to bring. Thus, organic solar cells (OSCs) are expected to be an alternative technology suitable for portable devices, building integrated photovoltaics and flexible electronic devices because they can be fabricated using high-throughput roll-to-roll printing processes on the flexible substrates. In this study, we synthesized perylene diimide based electron acceptors and the effects of their molecular geometry on the performance of fullerene-free OSCs are investigated. By incorporation of a 2,5-difluorobenzene moiety in the conjugated backbones, the planarity of the conjugated core is enhanced and the energy levels of the acceptor are down-shifted. In terms of molecular geometry, the difluorobenzene incorporated acceptor has a rigid core, which can symmetrically align the two perylene wings and enhance molecular packing. Furthermore, the incorporation of the difluorobenzene moiety effectively down-shifts the HOMO energy level, preventing back-transfer of holes from the acceptor to the cathode and enhancing the absorption of complementary wavelengths of the donor polymer, PTB7-Th. Leveraged by the beneficial geometric and energetic effects from the incorporation of difluorobenzene units, the power conversion efficiency of fullerene-free OSCs reached over 5%.
Preparation of Narrow-bandgap CuGaO2 Thin Films by Sol-gel Method
Muroran Institute of Technology, Japan
Delafossite CuGaO2 which belongs to wide bandgap oxide semiconductors plays a key role in the performance of p-type transparent conducting materials. On the other hand, wurtzite CuGaO2 is a narrow bandgap material and attracts attention as it is expected to be used in solar cell absorbers with higher efficiency. However, wurtzite CuGaO2 which in metastable form is difficult to prepare compared to a stable delafossite CuGaO2 . In this study, we report on the fabrication process of wurtzite CuGaO2 thin films by sol-gel method.
Firstly the Cu-O and Ga-O sol solutions been prepared separately by using copper (II) acetate monohydrate, tris acetylacetonate gallium (III), 2-propanol, and MEA. Then they were mixed using the stirrer for 3 min at 100 rpm at room temperature. After the solution was coated on Si or silica substrates, they were crystallized by the annealing at 280~350°C for 6h under N2 or air ambient.
The crystal structure and optical property of the films strongly depended on the annealing temperature and the power of the infrared furnace. Annealing temperature at 290~320°C under N2 flow, wurtzite CuGaO2 films had successfully being fabricated. The absorption spectrum of the films showed the direct transition property, and the optical bandgap energy was ~1.64 eV. But annealing temperature at 280℃, the red shift of the absorption edge was observed and CuGa2O4 phase was formed. As the increase of annealing temperature above 320℃, the films showed the indirect bandgap property and CuO phase became dominant. Furthermore, delafossite CuGaO2 films were fabricated at the high temperature of 800~950oC, and the sol solutions are useful for the sol-gel process of CuGaO2 based materials. By the controlling the annealing processes, narrow-bandgap CuGaO2 films with the wurtzite structure were successfully prepared without phase separation.
Raman Spectroscopy and Electrical Properties of Earth-Abundant Zn3As2 Nanoplatelets
1cole Polytechnique Fédérale de Lausanne (EPFL), Switzerland; 2Australian National University, Australia
The shortage of certain raw materials such as indium or gallium provides a strong impetus for the development of new semiconductors with properties as good or better than those in current commercial use . The development of such earth abundant semiconductors is particularly critical for large-scale photovoltaic applications. In this work, we explore one of the less well known earth abundant semiconductor materials with potential for photovoltaic application, zinc arsenide (Zn3As2).
Zn3As2 is a p-type semiconductor within the compound semiconductor’s II-V family. We investigated Zn3As2 nanoplatelets grown by Metal-Organic Vapor Phase Epitaxy (MOVPE) as in ref . Zn3As2 crystallizes in a body-centered tetragonal structure, leading to numerous vibrational modes. Raman spectroscopy measurements were conducted using various excitation wavelengths and the spectra obtained at these different wavelengths were compared. We derive Raman tensors for the given platelet configuration and compare them to the observed modes. We also discuss the possibility of using Raman spectroscopy for non-contact characterization of the hole mobility and density via hole-phonon coupling. Hole density and mobility were measured in a Van der Pauw configuration from room temperature down to 2K. We obtain a hole density of 1.31x1019 cm-3 at room temperature with mobility increasing to values of up to 820 cm2/Vs at lower temperatures. This study demonstrates a clear potential of nanoscale II-V semiconductors to become full-fledged members of the semiconductor materials range with direct interest for solar cell applications.
 S. Krohns, P. Lunkenheimer, S. Meissner, A. Reller, B. Gleich, A. Rathgeber, T. Gaugler, H. U. Buhl, D. C. Sinclair, and A. Loidl, Nat. Mater., 10, 899-901, (2011).
.T. Burgess, P. Caroff, Y. Wang, B.H. Badada, H. E. Jackson, L. M. Smith, Y. Guo, H. H. Tan and C. Jagadish, Nano Lett., 15, 378-385, (2015).
Si-based Up-Conversion Layers for an Efficient Light Management of Si Solar Cell
1CIMAP, Normandie Univ, ENSICAEN, UNICAEN, CEA, CNRS, France; 2Department of Mathematics, Statistics, and Physics, College of Arts and Sciences, Qatar University, Qatar
Silicon solar cells (Si-SC) dominate the photovoltaic market with an energy conversion efficiency of about 20%. To continuously be the major actor of the PV market, Silicon PV industry aims at lowering the cost process and increasing the SC efficiency. One of the ways to reach this objective is to reduce the existing mismatch between the solar spectrum and the energy that can be absorbed by a Si-SC. Thus using frequency conversion layers to overcome the transparency of Si-SC to photons with an energy lower than the Si bandgap could be an interesting solution.
The purpose of this paper is to detail the fabrication and study of Up-Conversion (UC) layers that convert two IR photons into a visible one that will be absorbed by the SC in order to increase its energy absorption range. Such layers consist in a Si-based matrix doped with Er3+ ions fabricated by a co-sputtering approach. The energy levels of Er3+ ions allow the absorption at 1.54µm and, if two Er3+ ions are close enough, a Förster energy transfer can occur allowing the emission of a photon at 980nm just above the Si bandgap. The low absorption cross section of Er can be overcome by adding an excess of Si in the layer and a 2D array of Ag nanoparticles with the objective to increase the photon conversion efficiency and therefore the SC efficiency. Optical characterizations such as FT-IR and photoluminescence have been carried out on UC layers to be able to optimize the system and to achieve a high conversion efficiency.
This work has been supported by the Qatar National Research Fund though the project Grant 8-1467-1-268.
Significance of Cobalt Doped Titanium Dioxide Thin films over Aluminium Doped Thin Films for Optoelectronic Applications
Mangalore University, India
Pristine, Aluminium and Cobalt doped Titanium Dioxide thin films were deposited on glass using sol-gel Spin Coating method. Thin Films prepared using a sol-gel process have been analysed for the different metal dopants. In addition, Uv-Visible spectroscopy, I-V studies, Atomic Force Microscopy (AFM), Ellipsometry, Photoluminescence, Scanning Electron Microscopy (SEM) and EDX were performed to characterize thin films. Uv-Visible spectroscopy study reveals that transmittance is high with cobalt doping and low energy gap of 3.1eV for Aluminium doped films. AFM confirm that surface roughness is high with the aluminium doped material. The resistivity of Co doped samples found to be low compared Al doped thin films. High transmittance and intermediate conductivity of cobalt doped TiO2 shows the significance in the optoelectronic application as a window layer.
Solution Processed Nano-Structured Cu2SnSe3 (CTSe) Thin Films, A Promising Candidate for Photovoltaic Applications
Materials Research Centre, Indian Institute of Science, India
We report the phase evolution of CTSe nano-crystals synthesized by solthermal approach from 120 oC to 200 oC using ethylenediamine as a solvent. XRD, Raman spectroscopy, HRTEM and SAED indicate that pure crystalline monoclinic CTSe phase was formed at 200 oC for synthesis duration of 24 hours with an average particle size of 23.06 ±6.27 nm and lattice parameters evaluated using Rietveld refinement revealed a=6.947Å, b=12.014Å, c=6.969Å, α=γ=90o and β=109.43o. The optical band gap was estimated as 1.30 eV and room temperature hall measurements revealed that CTSe is a p-type semiconductor with carrier concentration and mobility of 2.0×1018 cm3 and 6.41 cm2V-1s-1 respectively. The nano-crystalline CTSe are photo-sensitive under A.M 1.5G solar spectrum with sensitivity, responsivity, external quantum efficiency and detectivity of 71.14, 25.87 mA/W, 5.84% respectively under a bias of 1V. By increasing the bias voltage to 2V, we obtained the corresponding parameters as 39.55, 62.42 mA/W, and 14.04 % respectively. These findings highly suggest CTSe as a promising alternate solar energy absorber material.
Synthesis and Characterization of Cu3SbS4 Semiconducting Thin Films Grown by Co-Sputtering Metal Precursors and Subsequent Sulfurization
1Department of Condensed Matter Physics and Material Science, Tata Institute of Fundamental Research, India; 2School of Advanced Sciences, Vellore Institute of Technology-Chennai Campus, India; 3Department of Chemistry, Vellore Institute of Technology, India
Copper antimony sulfide (Cu-Sb-S, CAS) based ternary semiconductors are promising earth abundant materials for variety of applications in particular as p-type thin film absorber layers for heterojunction solar cells. The Cu-Sb-S material system exhibits four stable crystal phases with a direct bandgap ranging from 0.42–1.85 eV, high optical absorption (a > 105 cm-1) and p-type conductivity, which makes it ideal for thin-film solar cell absorbers. Further the bandgap of the materials can be tuned by changing the crystal structure. Among the different crystal phases of CAS, the famantinite (Cu3SbS4) phase is least explored and until now synthesized only as nanocrystals and nanofibers. In this work a systematic study on the growth and characterization of Cu3SbS4 thin films via a relatively simple two-step process of co-sputtering and subsequent sulphurization. The metal precursors with different Cu:Sb ratio are co-sputtered (thickness ~200 nm) on to a sapphire substrate by RF magnetron sputtering. The co-sputtered Cu-Sb samples are sealed in a quartz ampoule with excess chalcogen (0.1g). The quartz ampoule is evacuated to pressure of ~ 5 x 10-4 Pa using a diffusion pump and sealed, following which it is annealed in a wire-wound tubular furnace at temperature range of 200°C to 400°C with a heating rate of 10°C min-1. In our experiments different parameters like annealing temperature, dwell time and the composition of Cu-Sb alloy are varied and their influence on the film composition, morphology, structural and optical properties are studied using different characterization techniques like HR-XRD, SEM, TEM absorption spectroscopy and Raman spectroscopy.
Synthesis of Superhydrophobic Silica Nanoparticle Derived from Inorganic Polysilazane and Their Coating Layer Properties
Korea Institute of Industrial Technology, South Korea
A surface that exhibits a water contact angle of 150° or greater with very little flow resistance, such as observed for lotus leaves and the legs of water strides, was considered to have low wettability and fouling resistant. Besides, we have known that many kinds of surfaces such as butterfly wings, cicada wings and etc. have bumps, so that those make contact area of water minimize and a water resistance improve. These properties are attractive for many industrial application such as anti-sticking optical film, anti-snow accretion architectural coatings, windshields and dust-free coating for automobiles and etc. Nowadays, there have been a lot of research efforts on controlling roughness and morphology with nanoparticle and photolithography manufacturing process to obtain a superhydrophobic surface. Besides in the case of inorganic polysilazane as coating materials, it provides an excellent hardness and transmittance like glass after conversion thus it can be applied to functional film.
In this study, we synthesized fluorinated silica nanoparticle derived from inorganic polysilazane instead of StÖber method and diversified fluorine contents through verified the concentration of a 1H, 1H, 2H, and 2H-perfluorooctyltriethoxysilane (PFTES). The structure and surface properties of silica nanoparticle (13F-SiO2) derived from hydrolysis and polycondensation reaction of PHPS were studied by attenuated total reflection (ATR), X-ray photoelectron spectroscopy (XPS). We also measured their size and contact angle (sphere size: 10~30nm, Θ≥150°) with field emission-scanning electron microscope (FE-SEM), Transmission electron microscopy (TEM) and contact angle measurements. Besides, we formulated silica nanoparticle and inorganic polysilazane to form thin layer having high hardness and low wettability. That solutions were coated on PET film and exposed to an ammonia water solution for inducing oxidation reaction of inorganic polysilazane. And then we also analyzed on superhydrophobicity and optical properties of their coating layer.
Transition-Metal-Oxide Hole-Selective Contacts by RF Magnetron Sputtering for Heterojunction Silicon Solar Cells
1Polytechnic University of Catalonia, Spain; 2University of Barcelona, Spain
Heterojunction solar cells have already reached the highest efficiency for silicon-based solar cells. However, market share is still dominated by a rather traditional diffusion technology. Some reasons hindering the growth of heterojunction technology are the need for relatively complex deposition systems and hazardous gas precursors.
Recently, different materials have been proposed to replace doped amorphous silicon layers in a new kind of silicon-based heterojunction solar cells . Among them, transition-metal-oxides (TMO) arise as excellent hole-selective contacts. Particularly, molybdenum oxide (MoO3) has been widely studied in the literature as a selective hole-contact on n-type silicon wafers. Good results have been reported for MoO3 layers deposited by thermal sublimation , but this deposition technique is less suitable for upscaling.
In this work, we investigate the alternative use of radiofrequency magnetron sputtering as a more reliable deposition technique. Our initial studies have confirmed that MoO3 layers can be deposited by sputtering with excellent reproducibility and transparency. X-ray photoelectron spectroscopy analysis indicates suboxidized MoOx films (x≈2.4), as it is required to obtain semiconducting character. First heterojunction structures characterized by transient photoconductance have lifetimes of 40 µs, that is, moderate surface recombination of about 600 cm/s. Preliminary devices show excellent rectifying behaviour and good photocarrier collection. The final work will include results on complete solar cells.
 J. Bullock, M. Hettick, J. Geissbühler, A. J. Ong, T. Allen, C. M. Sutter-Fella, T. Chen, H. Ota, E. W. Schaler, S. De Wolf, C. Ballif, A. Cuevas, and A. Javey, “Efficient silicon solar cells with dopant-free asymmetric heterocontacts”, Nat. Energy, vol. 1, p. 15031, Jan. 2016.
 L. G. Gerling, S. Mahato, A. Morales-Vilches, G. Masmitja, P. Ortega, C. Voz, R. Alcubilla, and J. Puigdollers, “Transition metal oxides as hole-selective contacts in silicon heterojunctions solar cells”, Sol. Energy Mater. Sol. Cells, vol. 3, pp. 109–115, 2016.
Influence of Ni co-catalyst on the Photocatalytic Activity of Cu Doped ZnS Quantum Dots
1National Institute of Technology Durgapur, India; 2University of Liverpool, UK
In recent years many clean and renewable forms of energy technologies have come to the limelight because of the increasing energy crisis throughout the world due to limited stock of fossil fuels. Photocatalytic water splitting has evolved as one of the promising forms of renewable energy as it uses the most available raw material in the universe i.e water. Zinc sulphide is one of the most studied photocatalysts because of its fast electron hole-pair generation under photoexcitation and high photocatalytic activity for H2 production under UV light, environment friendly nature and earth abundance. However, it is practically inactive under visible light. Therefore, sometimes it is doped with transition metals like Ni, Cu, etc helps to lower its bandgap. Photodeposition of co-catalysts such as Pt, Ag, Ni, etc. has also been shown to improve the photocatalytic activity of ZnS as it lowers activation energy, which in turn increases the electron-hole pair separation at the co-catalyst-semiconductor interface. The purpose of this work is to study the influence of dopant and co-catalysts on the photocatalytic activity of ZnS quantum dots.
We report a simple synthesis route for introducing Cu2+ ions into the ZnS lattice to narrow its bandgap. XRD, XPS, HRTEM, EDAX, UV-vis spectroscopy characterizations were performed on the prepared samples. The analysis revealed that the internal quantum efficiency increases along with enhanced hydrogen production as we increase the dopant concentration upto the optimum concentration of 2 mole% compared to those of undoped ZnS. The performance of photocatalytic activity was found to improve further by photodeposition of Ni nanoparticles as co-catalyst under UV irradiation and the optimized performance was obtained for 10 nM of Ni precursor.
Investigation of Jsc Improvement in Solution Processed Cu2MnxZn1-xSnS4 with Efficiency > 5%
School of Materials Science and Engineering, Nanyang Technological University, Singapore
Cu2ZnSnS4 (CZTS) kesterite thin film solution processed serves as an alternative earth abundant, non-toxic and low cost absorber layer for thin film solar cell. However, existence of secondary phase limits the performance of current CZTS below its theoretical Shockley Quiesser power conversion efficiency limit of more than 30%. Existence of low formation energy secondary phase, such as ZnS, restricts optimum light absorption by CZTS which confines the current generated in the device. Introduction of Mn to partially replace Zn minimizes formation of low energy secondary phase and optimizes formation of CZTS. In this study, solution based Cu2MnxZn1-xSnS has been fabricated with different Mn/Zn ratios to understand the effect of Mn substitution on the device performance and intrinsic properties of the thin film. The study shows enhancement of short circuit current (Jsc) from 14.76 mA/cm2 to 16.63 mA/cm2 which leads to improved efficiency of 5.43% (active area efficiency of 5.88%). X-ray diffraction (XRD) pattern confirms that Mn substitutes for Zn in the crystal lattice of CZTS. Insignificant change in band gap at optimum Mn content is recorded by IPCE measurement. Energy-dispesive X-ray (EDX) validates the purity and elemental composition of the device. To further understand how Mn affects the carrier transport properties and defects energetics, a combination of AC Hall measurement, Time-resolved Photoluminescence (TR-PL) and Raman spectroscopy will be presented.
APbX3 (A= MA, FA) are Potential Candidate for High Efficiency Perovskite Solar Cells: A Review
University of Rajasthan Jaipur, India
Perovskite solar cell, which includes a perovskite structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material as the light-harvesting active layer. Perovskite materials such as methylammonium lead halides (MAPbX3) are cheap to produce and simple to manufacture. Solar cell efficiencies of devices using these materials have increased from 3.8% in 2009 to more than 22.1% in end of 2016,making this the fastest-advancing solar technology to date. The most commonly studied perovskite absorber is MAPbX3 (X = I, Br or Cl), with an optical bandgap between 1.5 and 2.3 eV depending on halide content. In recent years Formamidinum lead trihalide (H2NCHNH2PbX3) has also shown promising presence, with bandgaps between 1.5 and 2.2 eV for this technology. The minimum bandgap is closer to the optimal for a single-junction solar cell than methylammonium lead trihalide, so it should be capable of higher efficiencies. A common concern is the inclusion of lead as a component of the perovskite materials; solar cells based on tin-based perovskite absorbers such as MASnI3 have also been reported with lower power-conversion efficiencies. In recent developments, solar cells based on transition metal oxide perovskites and heterostructures such as LaVO3/SrTiO3 are studied and shows good conversion efficiencies. With the potential of achieving even higher efficiencies and the very low production costs, perovskite solar cells have become commercially attractive material for start-up companies already promising modules on the market in future.
Tailoring the Morphology of Photoactive Layer for High Performance Polymer Solar Cells
1Future Industries Institute, Division of Information Technology, Engineering and Environment, University of South Australia, Australia; 2Center for Advanced Photovoltaics, Department of Electrical Engineering and Computer Science, South Dakota State University, United States; 3Research Institute of Advanced Energy Technology, Kyungpook National University, South Korea; 4Department of Chemistry Education, Kyungpook National University, South Korea
Nanoscale morphology plays a crucial role in realizing highly efficient bulk heterojunction (BHJ) based polymer solar cells (PSC). The morphology of photoactive layer can be manipulated by optimizing the processing conditions like host solvent, solvent/thermal annealing and incorporation of solvent/solid additives to accentuate higher power conversion efficiency (PCE). In this work, we introduce a new organic solid additive (2,3-dihydroxypyridine, DOH) with adequate interactions into the poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) and phenyl-C61-butyric acid methyl ester (PCBM) photoactive blend system in order to alter the nanoscale morphology and to boost the photovoltaic (PV) performance of inverted BHJ based PSC. The additive, DOH modified PDPP3T:PCBM device exhibits better optoelectronic characteristics than that of the pristine (PDPP3T:PCBM) device fabricated from neat dichlorobenzene. The influence of additive casted PDPP3T:PCBM thin films on the optical, morphology and structural features are studied and correlated with PV characteristics to elucidate the associated mechanistic roles on the device enhancement. Topography images through Atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) reveal that the incorporation of additive into PDPP3T:PCBM provides finer nanoscale phase segregation of the polymer and fullerene phases with fibrillar morphology. The PV performance of the DOH processed PDPP3T:PCBM devices are evaluated by current-voltage (J-V) characteristics and compared with pristine and DIO-modified PDPP3T:PCBM devices. Interestingly, the incorporation of DOH (0.5 weight %) into PDPP3T:PCBM device witnessed a consistent and PCE of 6.36%, which is significantly higher than that of the reference (3.76%) and DIO-modified devices (4.75%). In addition, the photoinduced current extraction by linearly increasing voltage measurements demonstrate that DOH incorporated devices possesses higher mobility and extracted charge carrier density as compared to those of reference device. It is expected that further studies on the working mechanism of DOH would lead to higher efficiencies in other low band gap BHJ based PSC.
CIGS Solar Cells on Stainless Steel: the Substrate’s Effect on Performance
1Arizona State University, USA; 2Argonne National Laboratory, USA; 3MiaSolé Hi-Tech Corp, USA
The deposition of Cu(In,Ga)Se2 (CIGS) solar cells on stainless steel (SS) substrates has been of interest for quite some time due to the compatibility of thin-film deposition methods with flexible substrates and module efficiencies capable of 17% []. In comparison to devices using glass substrates, flexible CIGS solar cells can be used in a wide array of custom applications that take advantage of their reduced weight, portability and low production costs through large-scale roll-to-roll processing [, ]. Studies on the influence of stainless steel on the performance of CIGS devices have predominantly focused on metal impurity diffusion of elements from the stainless steel, particularly iron, into the CIGS layer . However, still little is known regarding the effect of the substrate’s composition, structure, and topology on the final device performance.
In this work, we perform a correlative pixel-by-pixel analysis at the nanoscale comparing X-ray fluorescence (XRF) and X-ray beam induced current and voltage (XBIC and XBIV) measurements of industry relevant flexible CIGS devices. Through 2-dimensional high-resolution mapping of XRF spectra and XBIC/XBIV, we correlate elemental distributions of the absorber layer and the majority elements in stainless steel to the local performance of the solar cell.
Through our analysis, we have observed regions of positive, negative, and no correlation between cation concentration and stainless steel element distribution, and XBIC/XBIV results. This contribution provides insight into the distinct relationships that exist between the stainless steel substrate composition, structure and topology, the elemental distributions in the CIGS absorber layer, and solar cell performance.
 MiaSolé Launches Flex Series Modules At SPI. Retrieved October 14, 2016, from http://www.pv-magazine.com
 Kessler, F., et al. (2005). Approaches to flexible CIGS thin-film solar cells. Thin Solid Films.
 Shi, C., et al. (2009). Cu(In,Ga)Se2 solar cells on stainless-steel substrates covered with ZnO diffusion barriers. Solar Energy Materials and Solar Cells