Suppressed Trap Densities and Excellent Carrier Dynamics of Germanium-Doped Lead Free Perovskites Revealed by Thermally Stimulated Current
Chi Huey Ng a, Satoshi Iikubo a, Qing Shen b, Kenji Yoshino c, Takashi Minemoto d, Shuzi Hayase a
a Kyushu Institute of Technology, Graduate School of Life Science and Systems Engineering, 2-4 Hibikino, Wakamatsu-ku, Kitakyushu-shi, 808-0196, Japan
b Graduate School of Informatics and Engineering, University of Electro-Communication, 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585, Japan.
c Faculty of Engineering, University of Miyazaki, Gakuen-kibanadai-nishi-1-1, Miyazaki, 889-2192, Japan.
d Department of Electrical and Electronic Engineering, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, 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
Poster, Chi Huey Ng, 086
Publication date: 23rd October 2018

The distribution of trap states within the perovskite vicinity is the primary factor which causes carrier dynamics inferiority and low photovoltaic performances. Two important criterions are to be emphasized in this work, which are first to investigate the role of SnF2 in suppressing Sn vacancy and secondly, to elucidate the effect of Ge dopant over the trap states and charge transport within the perovskite solar cell, which are revealed through thermally stimulated current (TSC) and its complementary analyses.

The suppression of Sn2+ oxidation process is proven through the XPS analysis where the Sn2+/Sn4+ ratio has substantially reduced upon the addition of SnF2. Corroboratory, weight loss at 150 ºC observed from the thermogravimetric profile of FMSI(0) without SnF2 has again emphasized the impact of SnF2 addition. From the viewpoint of trap density, we found that the addition of 5 mole percent Ge has significantly reduced the total trap densities from 1.93x1021 cm-3 (without Ge) to 1.80x1017 cm-3. Interestingly, the FMSGI(5) perovskite exhibits indistinguishable trap densities profile from that of MAPbI3 perovskite and exhibits a long charge diffusion length and high mobility of 1 μm and 98.27 cm2V-1s-1, respectively. In addition, the 5 mole% Ge-doped perovskite exhibited long-lived carrier lifetime of Ʈavg = 5.09 ns than the perovskite without Ge dopant (Ʈavg = 3.51 ns), implies the effectiveness of Ge in passivating the trap states. This work provides deep intuitive on trap landscape, which is important for the performance enhancement of lead free perovskite solar cells. 

This research was supported by JST MiraiProgram

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