Two-dimensional Ruddlesden-Popper (2D RP) layered metal-halide perovskites have garnered increasing attention due to their favorable optoelectronic properties and enhanced stability in comparison to their three-dimensional counterparts. Nevertheless, precise control over the crystal orientation of 2D RP perovskite films remains challenging, primarily due to the intricacies associated with the solvent evaporation process. In this study, we introduce a novel approach known as reverse-cool annealing (RCA) for the fabrication of 2D RP perovskite films. This method involves a sequential annealing process at high and low temperatures for wet perovskite films. The resulting RCA-based perovskite films show the smallest root-mean-square value of 23.1 nm, indicating a minimal surface roughness and a notably compact and smooth surface morphology. The low defect density in these 2D RP perovskite films with exceptional crystallinity suppresses non-radiative recombination, leading to a minimal non-radiative open-circuit voltage loss of 149 mV. Moreover, the average charge lifetime in these films is extended to 56.30 ns, thanks to their preferential growth along the out-of-plane direction. Consequently, the leading 2D RP perovskite solar cell achieves an impressive power conversion efficiency of 17.8% and an open-circuit voltage of 1.21 V. Additionally, the stability of the 2D RP perovskite solar cell, even without encapsulation, exhibits substantial improvement, retaining 97.4% of its initial efficiency after 1000 hours under a nitrogen environment. The RCA strategy presents a promising avenue for advancing the commercial prospects of 2D RP perovskite solar cells.

To improve the performance of inverted perovskite solar cells, we introduce a novel approach to enhance the devices’ efficiency notably. Our novel strategy incorporates a cutting-edge metasurface-based reflector featuring TiO 2 nanodiscs within a MoSe 2 layer, employed as an electron transport layer (ETL). Demonstrating a substantial improvement in light reflection from the lower part of the structure, the TiO 2 nanodiscs as a metasurface-based reflector enhance electron transfer. Notably, the metasurface-based perfect reflector, incorporating TiO 2 nanodiscs, outperforms other TiO 2 nanocube variations with an impressive light reflectance of 97.95%. Exploring different materials for electron transport layers (ETLs) and hole transfer layers (HTLs), we identify MoSe 2 as a potent secondary absorbent material, featuring a smaller bandgap than the primary absorbent MAPbI 3, thereby intensifying the electric field within the active layer and improving Power Conversion Efficiency (PCE). In the final evaluation, our inverted metasurface-based device structure (ITO/Cu 2O (HTL)/MAPbI 3/TiO 2 nanodiscs and MoSe 2 (ETL)/aluminum/SiO 2) significantly enhances the solar cell’s electrical characteristics compared to the planar reference structure (ITO/CuSCN/MAPbI 3/TiO 2/aluminum), with noteworthy increases in J sc, V oc, and PCE values from 17.98 mA/cm 2 to 21.91 mA/cm 2, 1.03 V to 1.07 V, and 15.33% to 19.17%, respectively. Our proposed inverted metasurface-based device structure represents a promising potential in the construction of high-performance perovskite solar cells.