Spatiotemporal Molecular Control of Crystallization for Efficient Perovskite/Organic Tandem Photovoltaics

Perovskite/organic tandem solar cells (PO-TSCs) offer a route toward overcoming the efficiency limitations of single-junction photovoltaics. However, wide-bandgap (WBG) perovskite sub-cells limit their performance, where uncontrolled crystallization leads to compositional heterogeneity, defect accumulation, and severe halide phase segregation. Here, we develop a template-bridge dual-control (TBDC) strategy using 2-thiophenemethylammonium bromide (2-ThMAB). Precisely controlling the introduction timing and spatial distribution of 2-ThMAB maximizes molecular regulation of crystallization. Surface-anchored 2-ThMAB molecules act as growth templates to induce (100) crystal growth, while grain-boundary-localized molecules regulate halide migration through molecular bridging, enabling homogeneous crystallization. The WBG perovskite films exhibit enhanced out-of-plane (100) orientation, reduced defect density, and suppressed halide phase segregation. Consequently, the optimized WBG device achieves a champion power conversion efficiency (PCE) of 20.13% with improved operational stability. Integrated into PO-TSCs, the optimized WBG sub-cells deliver a PCE of 26.62%. This strategy enables concurrent control of crystallization and halide redistribution of efficient, stable tandem photovoltaics.