Charge separation and recombination dynamics in Sn/Pb halide perovskite solar cell: uncovering the bottleneck of the photovoltaic efficiency

Witoon Yindeesuk^a, Taro Toyoda^a, Qing Shen^a, Kosei Fujiwara^b^,^c, Syota Tsukamoto^b^,^c, Shuzi Hayase^b^,^c, Yuhei Ogomi^b^,^c, kenji Katayama^d, Koki Sato^d, Kenji Yoshino^e

^aThe University of Electro-Communications, Japan, Japan

^bKyushu Institute of Technology, Japan, 204 Hibikino Wakamatsu-ku, Kitakyushu - Fukuoka, 808, Japan

^cCREST, JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan

^dChuo University, Tokyo 112-8551, Japan

^eMiyazaki Unversity, Miyazaki 889-2192, Japan

Proceedings of International Conference Solution processed Semiconductor Solar Cells (SSSC14)

Organizers: Henry Snaith and Samuel Stranks

Oral, Qing Shen, presentation 044
Publication date: 1st July 2014

Organometal trihalide perovskite-based solid-state hybrid solar cells have attracted unexpected increasing interest because of the high efficiency (the record power conversion efficiency has been reported to be over 17%) and low cost for preparation.¹⁾ The high efficiency was thought to mainly originate from the strong optical absorption over a broader range (up to 800 nm for Pb perovskite ) and longer lifetimes of photoexcited charge carriers (in the order of 10 ns – 100 ns) of the organometal trihalide perovskite absorbers. Recently, Hayase and coworkers have succeeded in harvesting energy in the NIR region by using Sn/Pb cocktail halide based perovskite materials covering up to 1060 nm and an efficiency of 4.18 % was achieved.²⁾ To improve the photovoltaic performance of Sn/Pb halide based perovskite solar cells, charge separation and recombination dynamics are key factors and should be understood deeply. In this paper, we have studied and clarified charge separation and recombination dynamics of Sn/Pb halide based perovskite solar cell using transient absorption (TA) techniques. CH₃NH₃Sn_0.5Pb_0.5 I₃ was deposited onto mesoporous TiO₂ substrates using one step method and P3HT was used as a hole transport material.²⁾ We found that ultrafast charge separation in a time scale of 1 ps was observed at both the TiO₂/CH₃NH₃Sn_0.5Pb_0.5I₃ and CH₃NH₃Sn_0.5Pb_0.5I₃ /P3HT interfaces. On the other hand, charge recombination at TiO₂/CH₃NH₃Sn_0.5Pb_0.5I₃ and CH₃NH₃Sn_0.5Pb_0.5I₃/P3HT interfaces occurred in a time scale of 10 μs and 16 ps, respectively. Our results indicate that the bottleneck of photovoltaic efficiency in Sn/Pb cocktail halide based perovskite solar cell is the recombination rather than charge separation and the efficiency can be improved by suppressing the recombination (especially that at CH₃NH₃Sn_0.5 Pb_0.5I₃/P3HT interface) through appropriate surface passivation and interfacial engineering.

References:1a) H. J. H. Noh, et.al., Nano Lett., 2013, 13, 1764; 1b) S. Kim, et.al., Sci. Rep.2012, 2 . 591 2012/ DOI: 10.1038/srep00591; 1c) J. Burschka, et.al., Science, 2012, 338, 643; 1d) J. M. Ball et.al., Energy Environ. Sci.,2013, 6, 1739; 1e) D. Liu, et.al., Nature Photonics, 2013,342 DOI: 10.1038; 1f) H. J. Snaith, et.al., J. Phys. Chem. Lett., 2013, 4, 3623; 1g) M. Liu, et.al., doi:10.1038/nature12509; 1g) J. H. Im, et.al., Nanoscale 2011, 3, 4088. 2) Y. Ogomi et.al., J. Phys. Chem. Lett., 2014, 5, 1004.

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