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

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.