Pb free perovskite-SnGe mixed metal perovskite solar cell with 7.5 % efficiency and enhanced solar cell stability at air without encapsulation
Shuzi Hayase a, Nozomi Ito a, Muhammad Akmal Kamarudin a, Qing Shen b, Yuhei Ogomi a, Satoshi Iikubo a, Kenji Yoshino c, Takashi Minemoto d, Taro Toyoda b
a Kyushu Institute of Technology, Japan, 204 Hibikino Wakamatsu-ku, Kitakyushu - Fukuoka, 808, Japan
b University of Electro-Communications2, 1-5-1 Chofugaoka, Chofu, Tokyo182-8585, Japan
c Miyazaki University3, 1 Konohanadai-Nishi, Miyazaki, 899-2191, Japan
d Ritsumeikan University4, 1-1-1, Nojihigashi, Kusatsu, 525-8577, Japan
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV18)
Benidorm, Spain, 2018 May 28th - 31st
Organizers: Emilio Palomares and Rene Janssen
Oral, Shuzi Hayase, presentation 061
DOI: https://doi.org/10.29363/nanoge.hopv.2018.061
Publication date: 21st February 2018

Lead-based perovskite solar cells have revolutionized the field of thin-film solar cells showing certified efficiency as high as 22-23 %. Despite the high-efficiency of these lead-based perovskite solar cells, the problem associated from the toxic nature of lead has open a new research direction which focuses on lead-free perovskite materials. As an alternative, 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. However, Sn-based perovskites are known to have low stability in air in which tin readily oxidizes from +2 to +4 upon exposure to air leaving oxygen vacancies which act as traps. We propose a new type of Pb-free perovskite material based on mixed metal tin and germanium. A new type of perovskite having the structure of FA0.75MA0.25Sn1-xGexI3 (abbreviated as SnGe(x)-PVK has been successfully prepared. The structure was confirmed from the XRD and XPS measurement. The electrical and optical characteristics of the perovskite materials were evaluated using PA and UV-Vis measurement showed that the materials have Eg ranging from 1.40 to 1.53 eV which confirmed the hypothesis that these materials can be used for solar cell applications. The highest performance was obtained with Ge content of x = 0.05, showing JSC 19.50 mA/cm2, VOC of 0.42 V, FF of 0.41 and efficiency of 4.48 %. The enhanced performance of this device when compared to that of SnGe(0)-PVK (3.31 %) was attributed to the surface passivation by Ge. Best performance of SnGe(0.1)-PVK solar cell was 7.5%. Additionally, the stability in air has been improved significantly with the Ge doping, retaining 80 % of its original performance, remarkable stability enhancement, compared with 10 % retention for non-doped sample (SnGe(0)-PVK). This work provides a platform for further research on lead-free mixed metal SnGe based perovskite solar cells.

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