Intermediate-Phase-Mediated Homogeneous Crystallization of Wide-Bandgap Perovskite for Efficient Silicon/Perovskite Tandem Solar Cells.

Achieving compositionally homogeneous mixed-halide (I- and Br-) wide-bandgap (WBG) perovskite films is crucial for high-performance perovskite/crystalline silicon tandem solar cells (TSCs), yet the disparate crystallization kinetics of iodide- and bromide-rich phases readily induce halide segregation and inhomogeneous elemental distribution, thereby compromising the performance of TSCs. Herein, we employ 3,4,5-trifluorobenzeneboronic acid (3FBBA) as a multifunctional modulator that synergistically interacts with both organic cations and lead-halide octahedra via complementary hydrogen-bonding and coordination interactions, by which 3FBBA fundamentally modulates the formation mechanism of α-phase perovskite. It transforms the spontaneous, uncontrolled direct crystallization pathway into a well-regulated phase-transition process mediated by highly ordered intermediate phases. These well-structured intermediates act as well-defined pre-structural frameworks to guide the formation of high-quality α-phase perovskite. Benefiting from this strategy, the resultant WBG perovskite films possess enlarged grain size and reduced defect density, which suppress nonradiative recombination loss and accelerate charge transfer kinetics. As a consequence, a single-junction 1.66 eV WBG perovskite solar cell (PSC) achieves a high-power conversion efficiency (PCE) of 24.09%, while a two-terminal perovskite/silicon TSC delivers a champion PCE of 33.6%. Notably, the unencapsulated TSC maintains over 90% of its initial PCE throughout 571 h of continuous maximum power point tracking (MPPT) under ambient atmospheric conditions.