Modulation of photovoltage in mesoscopic perovskite solar cell by controlled interfacial electron injection

Abstract

Controlled interfacial electron injection was investigated by surface modification of mesoporous TiO₂ film with insulating thin ZrO₂ layer in a mesoscopic CH₃NH₃PbI₃ perovskite solar cell. Open-circuit voltage (V_oc) was linearly increased with increasing the thickness of the surface ZrO₂ film from 863 mV for the bare TiO₂ to 988 mV for the surface modified TiO₂ with 2.2 nm-thick ZrO₂ layer (V_oc was 1030 mV for the mesoporous ZrO₂), which was due to decrease in electron injection by thickening the surface ZrO₂ layer. Change in electron injection was confirmed by photoluminescence spectra. Charge collection was diminished with the surface ZrO₂ layer, which might be related to the limited electron diffusion length in the solution-processed perovskite layer due to the reduced injection into TiO₂. Fill factor was reproducibly improved by surface modification, which is due to increased shunt resistance. By the controlled electron injection method, a power conversion efficiency was improved from 11.7% to 13.6% by introducing 1.1 nm-thick ZrO₂ layer on the TiO₂ surface.