Multifunctional Cross‐Linked Polyurethane Polymer as Interface Layer for Efficient and Stable Perovskite Solar Cells

Abstract In the past decade, perovskite solar cells (PSCs) have made remarkable progress in improving power conversion efficiency (PCE). In order to further improve the photovoltaic performance and long‐term stability of PSCs, the interface layer is essential. A multifunctional cross‐linked polyurethane (CLPU) is designed and synthesized via the spontaneous quaternization of polyurethane and 1, 6‐diiodohexane on the surface of the perovskite layer. CLPU layer cannot only effectively induce secondary crystallization and passivate the surface defects of perovskite, reduce the non‐radiative recombination, but also effectively block the moisture invasion. By this strategy, Cs 0.05 FA 0.95 PbI 3 PSCs with excellent reproducibility, is realized, achieving a PCE of 23.14% with an open‐circuit voltage of 1.11 V, a short‐circuit current density of 25.69 mA cm −2 , and a fill factor of 0.81. In addition, the unencapsulated devices show enhanced stability in 35 ± 5% relative humidity (RH) near 3000 h and in 65 ± 5% RH over 700 h. This study provides valuable insights into the role of CLPU interface layer in PSCs, which are essential for the design of high‐performance devices.