Grains &gt; 2 µ<i>m</i> with Regulating Grain Boundaries for Efficient Wide‐Bandgap Perovskite and All‐Perovskite Tandem Solar Cells

Tandem perovskite solar cells represent a significant avenue for the future development of perovskite photovoltaics. Despite their promise, wide-bandgap perovskites, essential for constructing efficient tandem structures, have encountered formidable challenges. Notably, the high bromine content (>40%) in these 1.78 eV bandgap perovskites triggers rapid crystallization, complicating the control of grain boundary growth and leading to films with smaller grain sizes and higher defect density than those with narrower bandgaps. To address this, potassium tetrakis(pentafluorophenyl)borate molecules are incorporated into the antisolvent, employing a crystallographic orientation-tailored strategy to optimize grain boundary growth, thereby achieving wide-bandgap perovskite films with grains exceeding 2 µm and effectively eliminating surplus lead halide and defects at the grain boundaries. As a result, remarkable efficiency is achieved in single-junction wide-bandgap perovskite devices, with a power conversion efficiency (PCE) of 20.7%, and in all-perovskite tandem devices, with a two-terminal PCE of 28.3% and a four-terminal PCE of 29.1%, which all rank among the highest reported values in the literature. Moreover, the stability of these devices has been markedly improved. These findings offer a novel perspective for driving further advancements in the perovskite solar cell domain.