Interfacial modification engineering for efficient and stable MA-free wide-bandgap perovskite solar cells by grain regrowth

Wide bandgap (WBG) perovskites are a key component of perovskite-silicon and all-perovskite tandem solar cells, which provides an effective way to exceed the efficiency limit of single junction solar cells. However, the small perovskite grain size and large defect density of WBG perovskites suppress the further improvement of the device power conversion efficiency (PCE). In this work, we offer a grain regrowth and defect passivation (GRDP) strategy to inhibit the nonradiative recombination loss at the perovskite grain boundary and in bulk simultaneously. Introducing guanidine thiocyanate (GuSCN) by post-treating the perovskite film can address this issue. GuSCN promotes the regrowth of perovskite grains and makes the grain size of perovskites larger than 1700 nm, thus reducing the defect density of perovskite solar cells (PSCs) by one order of magnitude. Consequently, a MA-free opaque WBG PSC achieves 20.92% PCE with excellent stability, maintaining 95.4% of its initial PCE after 3384 hours in N2. Furthermore, we fabricated a four-terminal perovskite-silicon tandem solar cell and the champion device obtained 27.16% PCE. This work provides an effective way to improve WBG PSCs' performance, facilitating the commercial application of tandem solar cells. Introducing GuSCN reduces the defect density of perovskites by one order of magnitude. Consequently, an MA-free opaque wide-bandgap perovskite solar cell achieves 20.92% power conversion efficiency with excellent stability.