Selective Templating Growth of Wide‐Bandgap Perovskites via Vertical Additive Gradients for 26.51%‐Efficient Perovskite/Organic Tandem Solar Cells

Precise control over the crystallization and growth of wide‐bandgap (WBG) three‐dimensional (3D) perovskite is essential for achieving high photovoltaic performance and enabling efficient tandem solar cells (TSCs). Herein, we report a selective templating growth (STG) strategy utilizing trimethylsulfonium iodide (TMSI) to regulate the crystallization dynamics of WBG perovskites. The strong coordination and templating capability of TMSI facilitate the in‐situ formation of a one‐dimensional (1D) perovskite intermediate, which uniquely directs the preferential (100) orientation and enhancing the lattice coherence within the resulting 3D perovskite framework. Moreover, a vertical concentration gradient of TMS + ions modulates crystallization kinetics, extending the time window for halide homogenization while simultaneously enabling effective grain boundary passivation through anchored PbI 2 nanosheets. As a result, optimized WBG perovskite solar cells (PSCs) deliver a champion power conversion efficiency (PCE) of 19.71%, accompanied by an enhanced open‐circuit voltage ( V OC ) of 1.35 V and significantly improved photostability. When integrated into monolithic perovskite/organic TSCs, the devices achieve a notable PCE of 26.51%. This work establishes a mechanistically grounded strategy for regulating perovskite crystallization through intermediate‐phase templating, offering a viable pathway toward high‐performance WBG absorbers for the next‐generation multi‐junction photovoltaics.