Dimensional Seed Engineering of Strain in Wide-Bandgap Perovskites for Efficient and Stable Tandem Solar Cells

Wide-bandgap (WBG) perovskites are essential for all-perovskite tandem solar cells, but their performance remains limited by defect-assisted nonradiative recombination, halide segregation, and residual lattice strain. Here, we develop a dimensional seed-guided strategy to regulate the crystallization pathway and strain state of WBG perovskites. Structurally defined one-dimensional (1D) and two-dimensional (2D) low-dimensional perovskite seeds are introduced into the precursor system, where they promote preferential crystal development toward the (100) orientation and are associated with distinct in-plane residual strain states in the resulting films. Compared with the 1D (DPE)0.5PbI3 (DPE: 1,2-bis(4-pyridyl)ethane) seed, the 2D (APD)PbI4 (APD: 1,2-bis(4-pyridyl)hydrazine) seed shows stronger interfacial coupling with the 3D WBG lattice and is associated with a more regular compressive residual strain state. This seed-regulated structural evolution correlates with reduced defect activity, suppressed ionic response, improved phase stability, and lower nonradiative loss. As a result, the optimized WBG perovskite solar cells achieve a champion power conversion efficiency (PCE) of 20.83% with a fill factor of 84.72%. When integrated into all-perovskite tandem solar cells, this strategy yields a champion PCE of 29.47% and 92.4% retention after 900 h of continuous maximum-power-point tracking under 1-sun illumination. These results highlight structurally defined crystal seeds as an effective handle for coupling crystallization control with strain-state modulation in WBG perovskites.