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 twodimensional 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 degrees C under a nitrogen atmosphere. This study explicitly paves a novel and general strategy for developing high-performance lead-free PSCs.