ITO/SnO2 Interface Defect Passivation via Atomic Layer Deposited Al2O3 for High‐Efficiency Perovskite Solar Cells

Indium tin oxide (ITO) substrate is widely used as a transparent electrode in perovskite solar cells (PSCs). However, the intrinsic defects, especially on the ITO surface, are one of the most key factors to restrict the power conversion efficiency (PCE) of PSCs. Herein, a facile method to passivate the defects of the ITO/SnO 2 interface using an ultrathin aluminum oxide (Al 2 O 3 ) layer through atomic layer deposition, of which the film thickness is exactly regulated, is first demonstrated. With the optimized film thickness, carrier recombination at the ITO/SnO 2 interface is effectively suppressed within the three‐cycle Al 2 O 3 layer, which results in an improved charge carrier collection efficiency from the SnO 2 electron transporting layer to the ITO electrode. Furthermore, a thinner Al 2 O 3 film (one cycle) does not passivate the interface defect effectively, and a thicker Al 2 O 3 film (five cycles) retards the charge carrier extraction at the ITO/SnO 2 interface. The average PCE of the three‐cycle Al 2 O 3 ‐based PSC is 19.43%, among which the champion PCE is 20.24%, showing a significant improvement compared with the counterpart with an average PCE of 18.50%.