Perovskite solar cells consisting of mixed metal SnGe perovskite as light absorber and role of the Ge in the solar cell
Chi-Huey Nga a, Kengo Hamada a, Daisuke Hirotani a, Akmal Kamarudin a, Qing Shen b, Satoshi Iikubo a, Kenji Yoshino c, Takashi Minemoto d, Shuzi Hayase a
a Kyushu Institute of Technology, 204 Hibikino Wakamatsu-ku, Kitakyushu - Fukuoka, 808, Japan
b University of Electro-communications
c Miyazaki University, 1-1 Gakuen, Kibanadai-nishi, Miyazaki 889-2192, Japan
d Ritsumeikan University, 1-1-1 norohigashi Kusatsu, 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, Shuzi Hayase, presentation 007
Publication date: 23rd October 2018

Despite the high-efficiency of these lead-based perovskite (PVK) solar cells, the problem associated with the toxic nature of lead has open a new research direction focusing on lead-free perovskite materials. Tin has been proposed to replace lead. The highest efficiency obtained with Sn only perovskite was 9 % which was based on 2D and 3D mixture of FASnI3. We previously reported mixed metal SnPb-PVK solar cells with several % efficiency. The efficiency has been enhanced now up to 17-20%2. In this study, Pb of SnPb-PVK was replaced with Ge. The use of germanium-based perovskite in solar cell was realized by Krishnamoorthy et. al. The solar cell performance was 0.11 % for CsGeI3 and 0.20 % for MAGeI3. A theoretical study showed that a stable SnGe-PVK material absorbing the sunlight spectrum can be realized. The new type of SnGe mixed metal perovskite solar cells are reported with enhanced efficiency and stability. FA0.75MA0.25Sn1-xGexI3 (abbreviated as SnGe(x)-PVK) were used for the mixed metal SnGe-PVK3. The structure of Ge-doped Sn perovskite was discussed from the view point of band gap, conduction and valence band level, XPS analysis, and the Urbach energy. It can be concluded that many Ge atoms are located at the both of hetero-interfaces, which decreased hetero-interface resistivity and contributed to the enhancement of Jsc. For SnGe(0)-PVK device, the average Jsc was 17.61 mA/cm2 with 0.46 V of VOC, 0.41 of FF, and 3.31% of PCE. By doping with 5 wt% of Ge, the JSC increased to 19.80 mA/cm2 and FF was improved up to 0.55, leading to enhanced efficiency of 4.48 %. After optimization, 7.9% of SnGe(5)-PVK device is reported. In addition, the stability of solar cells in air has been improved significantly with the Ge doping, which would be brought about by passivation effect of GeOx on the PVK layer. The electrical properties including carrier density, carrier mobility and carrier diffusion length of GeSn-PVK were compared with those of Sn-PVK and Pb-PVK, and the efficiency for the GeSn-PVK in future study are discussed with the comparison of those of Pb-PVK solar cells.

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