20Abstract Discovery of Perovskite Photovoltaics and Recent Research Progresses Tsutomu Miyasakatowards Social ImplementationSince our first discovery of perovskite solar cell (PSC) in 2006-2009, the progress of its power conversion efficiency (PCE) has been incredibly fast achieving the present highest PCE of 27.0% that is comparable to the top efficiency of crystalline Si cell. The current R&Ds of PSCs are focused on molecular engineering, using organic molecules, for defect passivation at heterojunction interfaces. This engineering enables improvement of photovoltaic performance and device durability.1 We have been studying on the method of interfacial passivation with functional organic molecules, which enables high voltage output (close to theoretical limit) in photovoltaic performance with PCE>22%.2 For practical applications, the stability of the devices still remains a major challenge. Use of organic cations in halide perovskites and diffusible dopants in hole transport materials (HTMs) are responsible for low stability at high temperatures (>120oC). To solve this, all-inorganic compositions of perovskite and use of dopant-free HTMs are highly desired. Our device fabrication focused on inorganic CsPbX3 (X=I, Br) perovskites in combination of dopant-free conductive polymer HTMs (Fig.1).2 By molecular passivation at hetero-junction interfaces, CsPbI2Br PSCs achieved PCEs of >17% under 1 sun. As visible light absorber, they exhibit high PCEs >34% under indoor LED illumination,3 which is promising for applications in consumer electronics represented by IOT devices. With suitable passivation, the Cs-based cells work with high open-circuit voltage of 1.4 to 1.5V. As inorganic perovskites, lead-free compositions such as Ag-Bi halides and Ag-Bi sulfides also become an important target for the design of environmentally benign printable photovoltaic devices.4 For example, AgBiS2-based device with a low bandgap absorber exhibits high photocurrent density >34 mA/cm2 comparable with Si semiconductor devices (Fig.2).5The implementation of PCS in a low-carbon society strongly demands the adoption of lightweight solar modules, which have the potential to be installed in a wider range of locations. Thin plastic film-based PCSs are manufactured based on low-temperature material preparation which we have developed previously during our research of dye-sensitized solar cells.6 For module development, Ink-jet coating method is also applied to fabricate miniature integrated modules, which can work with high voltage outputs under indoor illumination (Fig.3). NIMS Award Winning Lecture 1Professor, Toin University of Yokohama
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