Charge extraction at carrier transport layers adjacent to perovskites is crucial for the optimization of perovskite solar cells. In particular, Sn-perovskites with no lead elements are known to struggle from charge extraction. Here, we report the effects of organic ligands such as FA and MA (FA = HC(NH2)2 + MA = CH3NH3 +) on charge separation at the interface between electron transport layers and perovskites. TiO2 mesoporous covering the tin-perovskites show significant changes in the electronic structure and built-in potentials according to the ratio of FA to MA. Through a local probe with potential and current mapping, charge transport has been intensively examined. The best cell in this study is obtained as 5.37% at FA/MA = 3:1 with only iodine at the halide sites. Even though the value itself is not comparable with lead halides, it could pave a new direction to improve lead-free perovskite solar cells.
Bibliographical noteFunding Information:
This research was supported by the NRF Basic Science Research Program funded by the Ministry of Science, Technology and ICT (grant NRF-2018R1A2B2003607) and the Ministry of Education (NRF-2018R1A6A1A03025340), Republic of Korea. In particular, W.J. acknowledges that this work was also supported by the Ewha Womans University research grant of 2019.
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