The performance of perovskite solar cells (PSCs) is extremely dependent on the morphology and crystallization of the perovskite film. However, the complete conversion of PbI₂ to perovskite and controlling the perovskite crystal size as well as its surface morphology are challenging in the conventional two-step sequential deposition method. We herein present a facile method involving the use of a polar solvent additive in an inter-diffusion two-step sequential deposition method to achieve a high-quality perovskite film. The results showed that the addition of a small amount of DMF solvent into the MAI precursor solution could help the complete conversion of PbI₂ to perovskite, and at the same time could also reduce the pinholes, improve the film morphology, increase the grain sizes and enhance the film absorption ability. The improved perovskite film quality results in the boosting performance of PSCs. Consequently, an optimized device with power conversion efficiency as high as 19.2% is obtained. This current method provides a highly repeatable route for enhancing the PSC performance with the inter-diffusion sequential solution deposition method.

In this work, efficient mixed organic cation and mixed halide (MA_0.7FA_0.3Pb(I_0.9Br_0.1)₃) perovskite solar cells are demonstrated by optimizing annealing conditions. AFM, XRD and PL measurements show that there is a better perovskite film quality for the annealing condition at 100 °C for 30 min. The corresponding device exhibits an optimized PCE of 16.76% with V_OC of 1.02 V, J_SC of 21.55 mA/cm² and FF of 76.27%. More importantly, the mixed lead halide perovskite MA_0.7FA_0.3Pb(I_0.9Br_0.1)₃ can significantly increase the thermal stability of perovskite film. After being heated at 80 °C for 24 h, the PCE of the MA_0.7FA_0.3Pb(I_0.9Br_0.1)₃ device still remains at 70.00% of its initial value, which is much better than the control MAPbI₃ device, where only 46.50% of its initial value could be preserved. We also successfully fabricated high-performance flexible mixed lead halide perovskite solar cells based on PEN substrates.

Bright red CsPbIBr₂ films possess intrinsic semitransparent features, which make them promising materials for smart photovoltaic windows, power curtain walls, top cells for tandem solar cells, and bifacial photovoltaics.