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Chuanjiang Qin1 2 Toshinori Matsushima1 2 Matthew Leyden1 2 Chihaya Adachi1 2

1, Kyushu University, Fukuoka, , Japan
2, Adachi Molecular Exciton Engineering Project, Kukuoka, , Japan

Organic-inorganic hybrid halide perovskites have emerged as an interesting class of materials that have excellent photovoltaic properties for application to solar cells. In the last four years, the power conversion efficiency of perovskite solar cells (PSCs) over 20% has recently been realized through systematic optimization of materials and fabrication processes. However, the stability of PSCs is still not satisfied to practical applications, and the actual degradation mechanisms of PSCs are not well understood. Here, we firstly investigate the degradation mechanisms of CH3NH3PbI3-based PSCs using a thermally stimulated current technique. We observed that a large density of hole traps is formed in PSCs degraded by continuous solar illumination and that the formation of hole traps is strongly related to the stability.1 One source of the traps is metallic lead resulting from photodegradation of CH3NH3PbI3 under continuous light irradiation. We greatly extended the lifetime of PSCs under standard laboratory weathering testing from 150 hours to 4000 hours by suppressing the formation of Frenkel defect-metallic lead.2 Furthermore, we revealed influence of phase transition on the device stability, and developed efficient and thermally stable PSCs under standard thermal cycling test.
Second, we focus on perovskite light-emitting diodes that are promising for the next generation of lighting and displays because of their low cost, excellent color purity, and high performance. Morphology and crystallinity engineering in 3D perovskite emitters has led to an external quantum efficiency of 8.5% for green emission. Alternatively, quasi-2D perovskites exhibit an efficiency up to 12% in the near-infrared region, but they have not yet delivered efficiencies higher than this in pure green devices. Here, we discuss quenching mechanism of excited states by the organic cation that is a major loss path and must be avoided to achieve high efficiencies. In our optimized devices, the external quantum and current efficiencies of the champion green-emitting devices reached over 10%. Our findings will provide guidance for the development of future high-performance opto-electronic perovskite devices such as lasing.

References
1 C. Qin, T. Matsushima, T. Fujihara, W. J. Potscavage, Jr., and C. Adachi, Advanced Materials, 28, 466 (2016).
2 C. Qin, T. Matsushima, T. Fujihara, and C. Adachi, Advanced Materials, 29, 1603808 (2017).

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