Water-Assisted Crystal Growth in Quasi-2D Perovskites with Enhanced Charge Transport and Photovoltaic Performance

Organic–inorganic hybrid quasi-2D perovskites have shown excellent stability for perovskite solar cells (PSCs), while the poor charge transport in quasi-2D perovskites significantly undermines their power conversion efficiency (PCE). Here, studies on water-controlled crystal growth of quasi-2D perovskites are presented to achieve high-efficiency solar cells. It is demonstrated that the (BA)₂MA₄Pb₅I₁₆-based PSCs (n = 5) processed with water-containing precursors display an increased short-circuit current density (J_sc) of 19.01 mA cm⁻² and PCE over 15%. The enhanced performance is attributed to synergetic growths of the 3D and 2D phase components aided by the formed hydration (MAI∙H₂O), leading to modulations on the crystal orientation and phase distribution of various n-value components, which facilitate interphase charge transfer and charge sweepout throughout the device. The water-assisted crystallization is further applied to triple cation-based (BA)₂(MA_0.8FA_0.15Cs_0.05)₄Pb₅I₁₆ quasi-2D perovskites, which generate a remarkable PCE of 18.04%. Despite the presence of water in the precursors, the devices exhibit a satisfactory thermal stability with the PCE degradation <15% under continuous thermal aging at 60 °C for over 500 h.