Realizing Efficient and Reproducible Lead-free Perovskite Solar Cells with Purified Precursor Materials and Modified Solution Process
Jiewei Liu a, Masashi Ozaki a, Shinya Yakumaru a, Taketo Handa a, Ryosuke Nishikubo b, Yoshihiko Kanemitsu a, Akinori Saeki b, Yasujiro Murata a, Richard Murdey a, Atsushi Wakamiya a
a Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
b Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 566-0871, Japan
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, Jiewei Liu, presentation 042
Publication date: 23rd October 2018

Organic-inorganic hybrid halide perovskites are promising photovoltaic (PV) materials with power conversion efficiencies (PCE) exceeding 23%. Although the toxic lead-based perovskite materials used in the leading perovskite solar cells (PSCs) are a significant impediment to commercialization, obtaining comparable performance using more environmentally friendly metals in place of lead has proven challenging. We are looking at Sn as a replacement for Pb, addressing key issues potentially holding back performance such as reagent purity and film morphology. The higher reactivity of SnI2 compared to PbI2 places additional importance on the purity of the reagents, and in the present work our perovskite films were fabricated from tin perovskite precursor materials such as solvent-coordinated tin halide complexes e.g. [SnI2(dmf)] (Figure 1a)[1] which we confirmed to have significantly higher purity than commercially available SnI2. The growth of smooth, high coverage perovskite films with high crystallinity is also important for high efficiency PSCs and we confirm that Sn-based perovskite films require modified fabrication methods compared to their lead analogs. We have developed two simple methods to improve tin halide perovskite film quality.[2] First, a hot antisolvent treatment (HAT) was found to increase the film coverage and prevent electric shunting in the photovoltaic device. Second, a solvent vapor annealing (SVA) step was noted to increase the average crystallite size. Both the morphology and the electrical properties of the perovskite films are improved as a result of the combined treatments, facilitating the fabrication of Sn-based perovskite solar cell devices with power conversion efficiencies of over 7% (Figure 1b). 

This work was supported by JST-ALCA (JPMJAL1603), COI, ERATO (JPMJER1302), and NEDO.

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