Modulating Crystallization in Quasi‐2D Ruddlesden–Popper Perovskite Materials for High‐Performance and Scalable Printed Perovskite Solar Cells

Quasi‐2D Ruddlesden–Popper (2DRP) perovskites offer improved environmental stability in relation to their 3D counterparts. However, their multiple‐quantum‐well structure and insulating organic spacers inherently limit vertical charge transport, significantly reducing device performance in scalable printed films. Herein, we employ methylammonium chloride (MACl) as a crystallization‐modulating additive to overcome these transport bottlenecks in ambient printed 2DRP perovskite solar cells (PSCs). Focusing on an n = 9 2DRP absorber, MACl modulates precursor interactions involving organic spacers and guides phase evolution during film formation. This modulation yields a highly uniform phase distribution dominated by large‐n 2DRP phases while enhancing crystallinity and vertical orientation. Consequently, trap‐mediated recombination is significantly suppressed, leading to enhanced carrier mobility and facilitating efficient photocurrent generation. As a result, the optimized 1 cm 2 printed 2DRP‐based PSC achieves a remarkable power conversion efficiency (PCE) of 14.4%, in relation to the negligible PCE (0.4%) of the control device. Furthermore, this strategy is successfully validated across various compositions ( n = 2, 4, 5, and 7), demonstrating a versatile and broadly applicable route for the development of high‐performance, scalable printed 2DRP‐based PSCs.