Mitigated front contact energy barrier for efficient and stable perovskite solar cells

Abstract

The large work function difference between indium tin oxide (ITO) and electron transporting layers (ETLs) in the n–i–p perovskite solar cells (PSCs) usually causes a front contact energy barrier (Φ_FC), which induces significant efficiency losses at the contacts. Here, we address this issue by developing a passivating contact structure with an atomic-layer-deposited aluminium oxide (Al₂O₃) interlayer between the ITO and ETL, where the positive fixed charges in the Al₂O₃ layers modulate Φ_FC in the PSCs. It is clarified that the mitigated Φ_FC modifies the charge carrier density distribution near the ETL/perovskite heterojunctions and therefore effectively reduces interface recombination losses in the device. As a result, the n–i–p champion PSC with Al₂O₃ shows an efficiency of up to 25.7% (certified efficiency 25.3%) with an improved photovoltage of 30 meV, in contrast to the control device. The deposited homogenous Al₂O₃ layer enables a 23.7% efficient 1-square-centimeter and a 21.7% efficient 4-square-centimeter n–i–p cell. In the meantime, the Al₂O₃ layer can block the migration of iodine ions in the perovskite layer into the ITO layers, which greatly improves the operational stability of the PSCs.