Recent discovery of organic-inorganic (also known as hybrid) perovskites such as CH3NH3PbX3 (X = Cl, Br, I) for photovoltaic devices has reached 20% in merely 3-5 years and offer extraordinary potential for clean sustainable energy technologies and in general low-cost optoelectronic devices. In spite of the recent progress there exists tremendous variability in the structural and optoelectronic properties of the hybrid perovskite thin-films across the globe. Crystallinity, defect density and impurities are in general determining factors for (opto) electronic properties, which are also highly dependent on the materials formation processes. Apart from these the stability and reliability of perovskite based devices remains open questions and perhaps will determine the fate of this remarkable technology in the longer run. In this talk, I will describe our recent work on a novel solution-processing technique termed as “hot-casting” to grow continuous, pin-hole free thin-films of organometallic perovskites with millimeter-scale crystalline grains. Photovoltaic devices show hysteresis-free response, with high degree of reproducibility, thus overcoming a fundamental bottleneck for hybrid perovskite devices. We carried out correlated electronic and optical spectroscopy characterization to understand the physical properties of that hot-casted film and the impact towards the solar cell performance. Extensive capacitance characterizations are also done on those devices and suggest the majority .defect states are localized near the interface and by modifying the interface, the device open circuit voltage can be improved and thus lead to improved efficiency. In addition, I will describe our most recent efforts on understanding the photo-degradation process in these systems. Results demonstrate that the degradation under illumination is reversible process. Since large grain-size perovskite thin-films are not limited by detrimental effects such as ion migration or defect assisted trapping as characterized above, it allows us to probe intrinsic photo-physical processes that lead to the degradation of PCE in perovskite solar cells.

Optoelectronic properties of large grain hybrid perovskites solar cells and device photo-stability

251st National Meeting (2016)

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