Reduced Recombination Losses in Evaporated Perovskite Solar Cells by Postfabrication Treatment

The photovoltaic perovskite research community has now developed a large set of tools and techniques to improve the power conversion efficiency (PCE). One such arcane trick is to allow the finished devices to dwell in time, and the PCE often improves. Herein, a mild postannealing procedure is implemented on coevaporated perovskite solar cells confirming a substantial PCE improvement, mainly attributed to an increased open‐circuit voltage ( V OC ). From a V OC of around 1.11 V directly after preparation, the voltage improves to more than 1.18 V by temporal and thermal annealing. To clarify the origin of this annealing effect, an in‐depth device experimental and simulation characterization is conducted. A simultaneous reduction of the dark saturation current, the ideality factor ( n id ), and the leakage current is revealed, signifying a substantial impact of the postannealing procedure on recombination losses. To investigate the carrier dynamics in more detail, a set of transient optoelectrical methods is first evaluated, ascertaining that the bulk carrier lifetime is increased with device annealing. Second, a drift‐diffusion simulation is used, confirming that the beneficial effect of the annealing has its origin in effective bulk trap passivation that accordingly leads to a reduction of Shockley–Read–Hall recombination rates.