Crystal Growth Regulation of 2D/3D Perovskite Films for Solar Cells with Both High Efficiency and Stability

Reducing the electronic defects in perovskite films has become a substantial challenge to further boost the photovoltaic performance of perovskite solar cells. Here, 2D (NpMA) 2 PbI 4 perovskite and 1‐naphthalenemethylammonium iodide (NpMAI) are separately introduced into the PbI 2 precursor solutions to regulate the crystal growth in a 2D/3D perovskite film using a two‐step deposition method. The (NpMA) 2 PbI 4 modulated perovskite film shows a significantly improved film quality with enlarged grain size from ≈500 nm to over 1000 nm, which greatly reduces the grain‐boundary defects, improves the charge carrier lifetime, and hinders ionic diffusion. As a result, the best‐performing device shows a high power conversion efficiency (PCE) of 24.37% for a small‐area (0.10 cm −2 ) device and a superior PCE of 22.26% for a large‐area (1.01 cm −2 ) device. Importantly, the unencapsulated device shows a dramatically improved operational stability with maintains over 98% of its initial efficiency after 1500 h by maximum power point (MPP) tracking under continuous light irradiation.