The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages (). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in by up to 100 millivolts. We achieved a high of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

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The highest efficiencies reported for perovskite solar cells so far have been obtained mainly with methylammonium and formamidinium mixed cations. Currently, high-quality mixed-cation perovskite thin films are normally made by use of antisolvent protocols. However, the widely used "antisolvent"-assisted fabrication route suffers from challenges such as poor device reproducibility, toxic and hazardous organic solvent, and incompatibility with scalable fabrication process. Here, a simple dual-source precursor approach is developed to fabricate high-quality and mirror-like mixed-cation perovskite thin films without involving additional antisolvent process. By integrating the perovskite films into the planar heterojunction solar cells, a power conversion efficiency of 20.15% is achieved with negligible current density-voltage hysteresis. A stabilized power output approaching 20% is obtained at the maximum power point. These results shed light on fabricating highly efficient perovskite solar cells via a simple process, and pave the way for solar cell fabrication via scalable methods in the near future.

The performance of perovskite photovoltaics is fundamentally impeded by the presence of undesirable defects that contribute to non-radiative losses within the devices. Although mitigating these losses has been extensively reported by numerous passivation strategies, a detailed understanding of loss origins within the devices remains elusive. Here, we demonstrate that the defect capturing probability estimated by the capture cross-section is decreased by varying the dielectric response, producing the dielectric screening effect in the perovskite. The resulting perovskites also show reduced surface recombination and a weaker electron-phonon coupling. All of these boost the power conversion efficiency to 22.3% for an inverted perovskite photovoltaic device with a high open-circuit voltage of 1.25 V and a low voltage deficit of 0.37 V (a bandgap ~1.62 eV). Our results provide not only an in-depth understanding of the carrier capture processes in perovskites, but also a promising pathway for realizing highly efficient devices via dielectric regulation.