The Relevance of Interlayers in Highly Efficient Perovskite Solar Cells
Yuhei Ogomi a, Daisuke Hirotani a, Ajay K. Baranwal a, Masahiro Moriya a, Teresa S. Ripolles a, Shuzi Hayase a, Qing Shen b, Kenji Yoshino c, Germà Garcia-Belmonte d
a Graduate School of Life Science and Systems Engineering, 2-4 Hibikino, Wakamatsu-ku, Kitakyushu, Fukuoka , 808, Japan
b The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo, 182, Japan
c University of Miyazaki, 1-1 Gakuen Kibanadai, Miyazaki, 889, Japan
d Institute of Advance Materials (INAM), Universitat Jaume I, ES-12006 Castelló, Spain
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Oral, Teresa S. Ripolles, presentation 070
Publication date: 7th November 2016

Recently, Perovskite Solar Cells have drawn attention due to the impressive increment of the power conversion efficiencies of up to 21%. Numerous interesting properties characterize this absorber such as direct band gap, high optical absorption, large dielectric coefficient, long photoexcited carrier lifetime, long diffusion lengths, very small urbach energy. Different device configurations including mesoporous and planar (regular or inverted structure) succeed in achieving good device performances, being different interfaces between materials in such architectures. In particular, we discuss the important role of the interface between perovskite layer and n-type or p-type transport layer in a mesoporous-TiO2 solar cells. To that end, a new current peak at forward bias in the dark current–voltage curves has been identified, which peak appears only under some specific experimental conditions. This behaviour was found in a standard perovskite solar cells with absorber layer methylammonium lead iodide CH3NH3PbI3 and hole transport material (HTM) spiro-OMeTAD, and other materials were analyzed, achieving similar trends. When the solar cells were kept for several seconds under short-circuit conditions before starting the reverse measurement, it is considered that shallow and/or deep trap states located at the interface are dynamically filled during the reverse voltage scan. This uncommon diode shape disappears when the above experimental conditions are not applied. Therefore, in order to reduce these traps, the perovskite layer was passivated and consequently enhanced the overall cell performance from 14.5% to 17.6%. The passivation effect may prevent recombination processes at perovskite/HTM interface, being the charge recombination time longer from 0.3μs for non-passivated perovskite solar cells to 60μs for perovskite-passivated solar cells. It was expected that the most serious charge recombination occurs at interface between perovskite/n-type, where light is absorbed intensively and electron/hole densities are high. However, these studies corroborate that the interface between perovskite and p-type material should be paid particular attention.

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