Buried Interface Modification via Guanidine Thiocyanate for High-Performance Lead-Free Perovskite Solar Cells

Tin perovskites with exceptional optoelectronic properties have gained tremendous attention in environmentally friendly solar cells. However, it is still challenging to fabricate high-quality tin perovskite films with preferred crystal orientation and low interface defects by solvent engineering. Herein, a buried interface modification strategy (BIMS) is proposed to modify the interfaces between the hole transport layer and perovskite film. GA+ ions form tailored two-dimensional perovskites at the buried interface, inducing the template growth of Sn perovskite crystals with preferential orientation along the (100) plane. Moreover, the thiocyanate (SCN–) ions generate strong electrostatic attraction with uncoordinated Sn2+ ions, affecting its localized electron density around the buried interfaces and enhancing vacancy formation energy. As a result, the highest power conversion efficiency (PCE) of the perovskite solar cells (PSCs) via BIMS reaches up to 8.6%. Interestingly, the unencapsulated PSC remains at 80% of the initial PCE for 600 h after continuous 1 sun illumination at 55 °C under a nitrogen atmosphere. This study explicitly paves a novel and general strategy for developing high-performance lead-free PSCs.