Highly Stable and Efficient Silver-bismuth Halide Material for Lead-free Perovskite Solar Cells
Ashish Kulkarni a, Ajay Jena a, Masashi Ikegami a, Tsutomu Miyasaka a
a Graduate School of Engineering, Toin University of Yokohama, 1614, Kurogane-cho, Aoba, Yokohama, Kanagawa, Japan 225-8503
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference on Perovskite and Organic Photovoltaics and Optoelectronics (IPEROP19)
Kyōto-shi, Japan, 2019 January 27th - 29th
Organizers: Hideo Ohkita, Atsushi Wakamiya and Mohammad Nazeeruddin
Oral, Ashish Kulkarni, presentation 152
Publication date: 23rd October 2018

After the seminal work from our group,1 the power conversion efficiency (PCE) of organic inorganic lead halide perovskite solar cells have surpassed 20%.2 Such steep rise in PCE is attributed to perovskite exceptional optoelectronic properties such as ambipolar charge mobility, long carrier diffusion length, low exciton binding energy etc. Despite of several advantages, lead perovskites suffer from long term stability and lead toxicity issue.2, 3 The organic component in lead-perovskite is hygroscopic and gets eliminate from the crystal structure upon exposure to moisture, heat and continuous light illumination leaving behind the lead iodide (non-photoactive component). The exposure of toxic lead to human environment can cause severe damage to nervous and reproductive system and is believed to be an obstacle for commercialization.4 Therefore, development of Pb-free light is vitally important. In this regards, three dimensional (3D) silver-bismuth halide (SBH) materials such as AgBi2I7 have emerged as a promising candidate. However, AgBi2I7 crystallizes at 150 OC and this leads to loss of BiI3 from the crystal structure. Hence obtaining phase pure AgBi2I7 is of critical importance to further evaluate its potential for photovoltaic applications. In the present work, we show solvent engineering approach to obtain phase pure AgBi2I7 thin film at relatively low temperature (90 OC). As a result, AgBi2I7 device incorporating dopant-free HTM demonstrated 2% efficiency with high reproducibility. Moreover the best performing device shows exceptional stability against 60% relative humidity for 70 days and continuous 1 Sun illumination (at maximum power point tracking) for 1 h. This study also reveals an important correlation between solvent-mediated adduct and performance and stability of AgBi2I7 based solar cells and can help in enhancing the performance and stability further, paving a way towards non-toxic lead-free solar cells.


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