Enhanced electrical performance of perovskite solar cells via strain engineering†

Abstract

Strain plays a pivotal role in determining the electronic properties and overall performance of perovskite solar cells. Here, we identify that the conventional crystallization process induces strain heterogeneity along the vertical direction within perovskite films due to the fast solvent evaporation at the gas–liquid interface, leading to a gradual crystallization from top to bottom. By combining experimental and modelling analyses, we find that this heterogeneity modulates the energy band landscape within the perovskite, consequently restricting charge transport within the film. We address this issue by incorporating a small amount of 2-([2,2′-bithiophen]-5-yl) ethan-1-aminium iodide into perovskites, which selectively binds with the lead halide octahedra in the top surface region, regulating spatial strain distribution in a manner that promotes favourable charge transport. Applying this strategy in formamidinium-cesium-based inverted cells, we achieve an efficiency of 25.96% (certified 25.2%), with a high electrical performance of 1.014 V, surpassing 88% of the Shockley–Queisser limit. The regulated strain also demonstrates a positive impact on device stability. The best encapsulated cell, operated at the maximum power point, retains 88% of its initial efficiency after aging under one sun illumination at 55 ± 5 °C for 1500 hours in ambient air.