10:30am - 11:00amInvited
Hybrid Organic-Inorganic Perovskites: Structural/Electronic Diversity and Opportunities for Semiconductor Design
1Duke University, United States; 2Tokyo Institute of Technology, Japan; 3University of Toledo, United States; 4Wuhan University, China; 5University of North Carolina, United States
Photovoltaic (PV) devices based on three-dimensional perovskites, (Cs, MA, FA)Pb(I, Br)3 (MA=methylammonium, FA=formamidinium), have attracted substantial recent interest, because of the unprecedented rise in power conversion efficiency to values above 20%, which in turn is made possible by the near ideal band gap, strong optical absorption, high carrier mobilities, long minority carrier lifetimes, and relatively benign defects and grain boundaries for the absorbers. Some of the same properties that render these materials near-ideal for PV, also make them attractive for LED and other optoelectronic applications. Despite the high levels of device performance, the incorporation of the heavy metal lead, coupled with issues of device stability and electrical hysteresis pose challenges for commercializing these exciting technologies. This talk will provide a perspective on and discuss recent advances related to the broader perovskite family, focusing on the extraordinary structural/chemical diversity, including ability to control structural/electronic dimensionality , substitute on the organic cation, metal or halogen sites, and prospects of multi-functionality and structure-property control arising from separately engineered organic/inorganic structural components (e.g., see ). Further exploration within the organic-inorganic hybrid space offers exciting opportunities for future energy and electronic materials design .
 Z. Xiao, W. Meng, J. Wang, D. B. Mitzi, Y. Yan, Mater. Horizon DOI: 10.1039/C6MH00519E (2017).
 B. Saparov and D. B. Mitzi, Chemical Reviews 116, 4558 (2016).
 D. B. Mitzi, K. Chondroudis, C. R. Kagan, IBM J. Res. Dev. 45, 29 (2001).
11:00am - 11:30amInvited
Rational Material Composition, Interface, and Device Engineering for High-Performance and Stable Perovskite Solar Cells
1City University of Hong Kong, Hong Kong S.A.R. (China); 2University off Washington, United States
Advances in controlled synthesis, processing, and tuning of the properties of organic conjugated polymers and peroskites have enabled significantly enhanced performance of organic and hybrid solar cells. The performance of hybrid perovskite solar cells is strongly dependent on their efficiency in harvesting light, charge transport, and charge collection at the metal/organic/perovskite or the metal/metal oxide perovskite interfaces. In this talk, an integrated approach of combining material design, interface, and device engineering to significantly improve the performance and stability of hybrid perovskite photovoltaic cells (PCE of >20%) will be discussed. At the end, several new device architectures and optical engineering strategies to make tandem cells and semitransparent solar cells will be discussed to explore the full promise of perovskite hybrid solar cells.
11:30am - 11:45amOral
Molecular Self-Assembly Fabrication and Carrier Dynamics of Stable and Efficient CH3NH3Pb(1−x)SnxI3 Perovskite Solar Cells
1Institute of New Energy Technology, College of Information Science and Technology, Jinan University, China; 2Institute of Photovoltaics, College of Physics Science and Technology, Hebei University, China
Despite CH3NH3PbI3 perovskite solar cells have recently exhibited a significant improvement in efficiency, the Sn-based perovskite solar cells still suffer from low efficiency and poor stability that derived from the oxidation of Sn2+.
Here, a series CH3NH3Pb(1−x)SnxI3 (0≤x≤1) perovskite thin films with full coverage were obtained via molecular self-assembly process. The intermediate complexes of PbI2/(SnI2)∙(DMSO)x were proved to retard the crystallization of CH3NH3SnI3, thus allowing the realization of high quality Sn-introduced perovskite thin films. We demonstrated that the electronic properties of CH3NH3Pb(1−x)SnxI3 (0≤x≤1) perovskite films, i.e., defect state density, carrier concentration, mobility and energy level, could be controllable by tuning the composition ratio of Pb/Sn. The external quantum efficiency (EQE) of as-prepared solar cells were demonstrated to extend a broad absorption minimum over 50% in the wavelength range from 350 to 950 nm accompanied by a noteworthy absorption onset up to 1050 nm. The CH3NH3Pb0.75Sn0.25I3perovskite solar cells with inverted structure were consequently realized with maximum power conversion efficiency (PCE) over 14% , which displayed hysteisis-free effect and stabilized power output (SPO) over 12% within 200 s at 0.6 V forward bias. Likewise, to further investigate the carriers dynamics along the entire pathway in the completed cells, we further inverstigated the surface and bulk recombination lifetime of carriers, as well as the transient photovoltage decay curves of devices, which were favorable to clearly understand the carrier dynamics and optimise the Sn-Pb mixed perovskite solar cells, e.g., (i) suppress carrier recombination in the absorber, (ii) facilitate carrier injection into the carrier transport layers, (iii) maintain good carrier extraction at the electrodes.
The present study is favorable to overcome the intractable issue concerning the toxic Pb element in perovskite solar cells and step forward toward realizing the lead-free perovskite solar cells with high efficiency.
11:45am - 12:00pmOral
Assessment of Cs3Bi2I9 as Lead-Free Photovoltaic Absorber Materials
1Nanyang Technological University, Singapore; 2The Australian National University, Australia
Lead-based perovskite compounds have gained tremendous interests in recent years for rich varieties of optoelectronic properties. Nevertheless, some of the major challenges such as inherent heavy metal toxicity due to lead and atmospheric stability have been huge hurdle for extensive application of lead-based perovskite. One approach to solve the problems is to find alternative compounds with similar optoelectronic properties. Bismuth is one of the key elements that possesses similar electronic structure as that of lead with the presence of ns2 electrons that exhibits rich structural variety as well as interesting optical and electronic properties.
Here, we investigated the optoelectronic properties of Cs3Bi2I9 as a candidate for thin-film solar cell absorber material. The bandgap of Cs3Bi2I9 was found to be indirect in nature and ~2 eV. However, the difference with direct bandgap is small which implies that absorption coefficient would be high. This property is highly desirable for thin-film solar cells. Nevertheless, the solar cell efficiency of the Cs3Bi2I9 as light absorber in mesoscopic solar cell configuration was found to be poor. We have further investigated the possible reasons of the poor performance by Transient Absorption and luminescence spectroscopy. The comparative photoluminescence studies between thin-films and single crystal highlight the presence of intrinsic defects in this compounds. However, we have shown that efficiency of the Cs3Bi2I9 solar cell can further be improved by changing the stoichiometry of the precursor solution.