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

Abstract

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.