Inverted perovskite solar cells with over 2,000 h operational stability at 85 °C using fixed charge passivation

High-quality defect passivation at perovskite/charge extraction layer heterojunctions in perovskite solar cells is critical to solar device operation. Here we report a ‘physical’ passivation method by producing fixed charges with aluminium oxide (negative fixed charges) or silicon oxide (positive fixed charges) interlayers grown by atomic layer deposition at perovskite/charge extraction layer heterojunctions. Through experimental and modelling approaches, we find that the fixed charge passivation (FCP) modifies carrier concentration distribution near the heterojunctions, which reduces interface recombination and photovoltage losses. The strong acidity of aluminium oxide simultaneously shields perovskites from being deprotonated by the nickel oxide at high temperatures. The optimized FCP device shows an efficiency of 22.5% with over 60 mV improvement in photovoltage in contrast to the control devices. Importantly, the encapsulated FCP devices, operated at the maximum power point, exhibit almost no efficiency loss after ageing under 1-sun illumination at 85 °C for 2,000 h in ambient air.