Stabilization of 3D/2D perovskite heterostructures via inhibition of ion diffusion by cross-linked polymers for solar cells with improved performance

Two-dimensional (2D) and quasi-2D modifications of three-dimensional (3D) perovskite active layers have contributed to advances in the performance of perovskite solar cells (PSCs). However, the ionic diffusion between the surface 2D and bulk 3D perovskites leads to the degradation of the 3D/2D perovskite heterostructures and limits the long-term stability of PSCs. Here we incorporate a cross-linked polymer (CLP) on the top of a 3D perovskite layer and then deposit a 2D perovskite layer via a vapour-assisted two-step process to form a 3D/CLP/2D perovskite heterostructure. Photoluminescence spectra and thickness-profiled elemental analysis indicate that the CLP stabilizes the heterostructure by inhibiting the diffusion of cations (formamidinium, FA + and 4-fluorophenylethylammonium, 4F-PEA + ) between the 2D and 3D perovskites. For devices based on carbon electrodes, we report small-area devices with an efficiency of 21.2% and mini-modules with an efficiency of 19.6%. Devices retain 90% of initial performance after 4,390 hours operation under maximum power point tracking and one-sun illumination at elevated temperatures.