Functional Analysis and Instructive Selection of a Green Additive Achieve Dual-Interface Modification for Fabricating Self-Powered, High-Performance Perovskite Photodetectors

The guanidine compound has recently been demonstrated to be effective in passivating interface defects and enhancing the performance and stability of perovskite photodetectors (PPDs). However, the selection and utilization of these compounds are conducted without comprehensive guidance due to an insufficient understanding of the mechanisms and functions of their functional groups. Herein, we evaluated the defect passivation capabilities of guanidine acid (Gua) by analyzing its electrostatic potential and molecular orbitals and then applied it at the interface of all-inorganic perovskite and SnO2 films. The smoother morphology, larger crystal, and improved optoelectronic properties of Gua-modified SnO2 and perovskite films demonstrated the effective defect suppressing of Gua. Moreover, systematic experiment and calculation analyses have revealed that the –C═NH group, with a higher electron cloud density, not only plays a dominant role in healing the oxygen vacancies, free hydroxyl groups, and Sn-related defects on the SnO2 surface but also passivates the Pb2+ and X– defects at the perovskite interface. Consequently, the Gua-modified all-inorganic PPDs achieve an exceptional detectivity of 1.32 × 1013 Jones, a responsivity of 0.30 A/W, and a minimal dark current of 1.55 × 10–9 A/cm2. This work provided valuable insights for customizing Lewis base molecules with crucial functional groups and a universal strategy to estimate and select organic molecules for perovskite photoelectronic devices.