Absorption edge of perovskite (PVK) solar cells consisting of MAPbI3 is 800nm. According to our simulation, light harvesting in the area of near IR is also necessary for enhancing the efficiency more. We have already reported that mixed metal perovskite (MAPbSnI3) shows photo-conversion in IR region (1-6). The short circuit current (Jsc) was high, reaching to 30 mA/cm2 because of the wide range of light harvesting. However, the open-circuit voltage (Voc) was lower than 0.3 V and the estimated voltage loss was 0.6-0.7 V, which was much larger than that of MAPbI3 (0.4 V), suggesting the presence of high density charge recombination center. We found that Ti-O-Sn bonds formed at the interface between Tiania and MAPbSnI3 layer, create trap states, resulting in increasing charge recombination at the interfaces. The surface trap density and the trap depth was quantitatively monitored by thermally stimulated current methods. When the Ti-O-Sn linkage was formed at the interface between TiO2 and PVK, the trap density increased by one order of magnitude. The interface was analyzed by XPS and confirmed that Ti-O-Sn linkage was formed. After removing the Ti-O-Sn bond at the interface between TiO2 and MAPbSnI3, the efficiency drastically increased from 4.0 % to 13.8 % and the stability was improved. It was proved that interface architecture is quite important for enhancing the MAPbSnI3 solar cells.
1. S. Nakabayashi, et al., J. Photonics for Energy; 2015, 5, 057410. 2. Y. Ogomi, et al., J. Phys. Chem. Lett. 2014, 5, 1004-1011.