Thermally Independent Interfacial Reconstruction for Phase‐Pure n = 1 2D Perovskites With Mixed‐Orientation Surface Architecture

Two-dimensional (2D) perovskites are widely employed to enhance the efficiency and stability of perovskite solar cells (PSCs); however, their formation typically relies on thermal annealing, which can degrade the underlying three-dimensional (3D) perovskite and lead to poorly defined phases. In addition, their intrinsically low out-of-plane conductivity imposes a trade-off between improved stability and efficient charge transport. Here, a thermally independent interfacial reconstruction strategy is reported to enable the phase-selective formation of phase-pure n = 1 2D perovskites without thermal activation. This approach suppresses thermally induced degradation and prevents the formation of higher-n or mixed-phase intermediates. The resulting 2D perovskite exhibits a mixed-orientation architecture, comprising domains parallel and tilted relative to the underlying 3D lattice. This structural configuration simultaneously enables effective surface passivation and ion-blocking while maintaining efficient vertical charge transport, thereby overcoming the stability-transport trade-off. As a result, the optimized PSCs achieve a champion efficiency of 26.61% and retain over 98% of their initial performance after 2000 h of continuous maximum power point tracking. In contrast, the control devices exhibit inferior efficiency and accelerated degradation under identical conditions. This work establishes a nonthermal pathway to reconcile stability and charge transport in perovskite optoelectronics.