Device Analysis of Lead-Halide Perovskite Solar Cells
Hideo Ohkita a, Hyung Do Kim a
a Kyoto University, Japan, Goryo-Ohara, Nishikyo-ku, Kyoto 615-8245, Japan
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics 2018 (AP-HOPV18)
Kitakyūshū-shi, Japan, 2018 January 28th - 30th
Organizers: Shuzi Hayase, Juan Bisquert and Hiroshi Segawa
Invited Speaker, Hideo Ohkita, presentation 010
DOI: https://doi.org/10.29363/nanoge.ap-hopv.2018.010
Publication date: 27th October 2017

Lead-halide perovskite solar cells have made rapid progress in the last few years.  Currently, the power conversion efficiency (PCE) has been improved up to more than 20%.  We have recently shown that the device performance is improved with increasing grain size of perovskite materials and with decreasing thickness of the hole-transporting layer (HTL).[1,2]  In this talk, we will discuss the photovoltaic parameters in CH3NH3PbI3 perovskite solar cells.  All the photovoltaic parameters were improved with increasing grain sizes of CH3NH3PbI3 perovskite materials.  The improvement in JSC is simply because the absorption efficiency is increased owing to the thicker active layer.  For the device with an active layer thickness of ~500 nm, the external quantum efficiency was as high as more than 90%, suggesting no loss in the current generation.  The improvement in VOC was well analyzed by direct and trap-assisted (Shockley−Read−Hall) SRH recombination model.  As a result, we found that VOC is mainly limited by the trap-assisted SRH recombination.  If trap density was reduced to less than 1013 cm−3 so that the trap-assisted recombination is negligible, VOC would be improved up to 1.27 V.  The fill factor was improved with decreasing HTL thickness as mentioned above.  As a result, the best performance was obtained for the device with an active layer thickness of ~500 nm and an HTL thickness of 170 nm: JSC = 23.8 mA cm−2, VOC = 1.07 V, FF = 0.770, and PCE = 19.6%.[2]  This improvement in FF can be explained by an empirical equation for FF with a reduced series resistance RS.  On the basis of the empirical equation, FF would be improved up to more than 0.8 for the highest VOC and lowest RS.  Consequently, we conclude that PCE could be improved up to more than 25%.

 

References:

1) H. D. Kim, H. Ohkita, H. Benten, and S. Ito, Adv. Mater., 28, 917–922 (2016).

2) H. D. Kim and H. Ohkita, Sol. RRL, 1, 1700027 (2017).

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