Efficiency-enhancement of lead-free ASnI2Br perovskite solar cells by phenyltrihydrosilane passivation effective for Sn4+ reduction and hydrophobization

The efficiency enhancement of the tin perovskite solar cell consisting of ASnI2Br (ASnI2Br-PVK-PV) is discussed. The ASnI2Br-PVK-PV has a bandgap wider than 1.6 eV and is applicable to the top layer of Pb free perovskite/Si tandem solar cells. The low efficiency of the ASnI2Br-PVK-PV is due to the presence of Sn4+ and defects at the hetero interfaces. We found that PhSiH3 solution treatment (passivation) of the film surface decreases the Sn4+ concentrated on the surface of the perovskite film. At the same time, PhSiH3 treatment (passivation) made the surface of the perovskite layer hydrophobic, resulting in giving better contacts between the perovskite layer and the hydrophobic C60 layer. The efficiency was enhanced from 3.65% to 5.50% after the passivation, proving the effectiveness of the PhSiH3 treatment. The mechanism of the passivation is discussed.