Grain Regrowth and Bifacial Passivation for High‐Efficiency Wide‐Bandgap Perovskite Solar Cells

Abstract The wide‐bandgap perovskite solar cell is a crucial part of perovskite/silicon tandem solar cells, which offer an avenue for surpassing the power conversion efficiency (PCE) limit of single‐junction silicon solar cells. However, the actual efficiency of such tandem solar cells today is diminished by the nonradiative recombination losses in the wide‐bandgap perovskite subcells. Here, this work reports a grain regrowth and bifacial passivation (GRBP) strategy to reduce recombination losses at the grain boundaries and perovskite/charge transport layer interfaces simultaneously. This is achieved by a posttreatment of perovskite films with a mixture of methylammonium thiocyanate (MASCN) and phenethylammonium iodide (PEAI). The MASCN induces the regrowth of perovskite grains and simultaneously facilitates the penetration of PEAI into the hole‐transport‐layer (HTL)/perovskite bottom interface. Thereby, the bulk and interface nonradiative recombination losses are reduced and the open‐circuit voltage in solar cells is considerably increased. PCEs of 21.9% and 19.9% for the 1.65‐eV bandgap opaque and semitransparent perovskite solar cells, respectively, are obtained. The encapsulated semitransparent perovskite solar cells retain their initial efficiency following 500 h of operation under one‐sun illumination in ambient conditions. The perovskite/silicon 4‐terminal (4‐T) tandem cells are fabricated with impressive PCEs 29.8% and 28.5% for 0.049 cm 2 and 1 cm 2 devices, respectively.