Mechanical strengthening of a perovskite–substrate heterointerface for highly stable solar cells

Abstract

Perovskite solar cells (PSCs) have shown power conversion efficiencies (PCEs) of over 26% that rival crystalline silicon cells, but their projected application was largely postponed by the device instability, particularly the degradation that originated from the defective bottom interfaces. Here, we introduce a cohesive guanidine polymer, as macromolecular glue, to strengthen the buried interface, resulting in a mechanically robust and passivated bottom interface. We found that the guanidine motifs can chemically couple the perovskite/substrate layers and remarkably restrict the interfacial ionic migration and morphology variation under an environmental stimulus. The resulting solar cells presented over 25% efficiency and maintained >97.5% of their initial efficiency in long-term operational stability tests with continuous 1-sun illumination at 55 °C for >1600 hours. The geometric impact of these nanostructures during solar cell degradation was further analyzed by finite element simulation, which revealed that the void expansion would disturb the charge carrier distribution and transport for inferior carrier collection and high recombination velocity. Our strategy offers valuable insights into the design and development of long-lifetime perovskite devices with robust and stable interfaces.