Expanded Phase Distribution in Low Average Layer‐Number 2D Perovskite Films: Toward Efficient Semitransparent Solar Cells

Abstract The application of low average layer‐number (〈 n 〉 ≤ 2) 2D perovskites in semitransparent photovoltaics (ST‐PVs) has been hindered by their strong exciton binding energy and high electrical anisotropy. Here, the phase distribution is expanded fully and orderly to enable efficient charge transport in 2D (NMA) 2 (MA)Pb 2 I 7 (NMA: 1‐naphthylmethylammonium, MA: CH 3 NH 3 + ) perovskite films by regulating the sedimentation dynamics of organic cation‐based colloids. Ammonium chloride is synergistically introduced to enhance the phase separation further and construct a favorable out‐of‐plane orientation. The wide and graded phase distribution well aligns the energy level to facilitate charge transfer. As a result, the first application of an average 〈 n 〉 = 2 2D perovskite is implemented in ST‐PVs with visible power conversion efficiency (PCE) of 7.52% and high average visible transmittance (AVT) of 40.5%. This study offers a new candidate and an effective strategy for efficient and stable ST‐PVs and is relevant to other perovskite optoelectronic devices.