Buried interface modified by guanidinium iodide for enhanced efficiency and stability of perovskite solar cells

A guanidinium iodide layer is deposited on SnO2 to modify the buried interface of SnO2/CH3NH3PbI3 in perovskite solar cells. It is found that hydrogen bonds are formed between GAI and SnO2, which not only reduce the defects of SnO2 but also anchor the GAI molecules on the surface of SnO2 and then functioned as nucleation sites to form a 2D perovskite layer at the SnO2/CH3NH3PbI3 interface. Moreover, GAI molecules are demonstrated to distribute at the grain boundaries in the whole perovskite film, and hydrogen bonds are formed between GAI and perovskite. These hydrogen bonds effectively suppress the charge trapping and recombination regions induced by the under-coordinated iodine species. A CH3NH3Cl additive is found to be essential in the perovskite precursor, which manipulates the crystal growth dynamic and the vertical crystallization and hence the improved morphology of the perovskite films. Dramatically increased efficiency and stability are demonstrated in the perovskite solar cells. The optimized device shows a more than 20% higher PCE than the reference device. Besides, the device also remains 80% of its initial efficiency after storage for 60 days, suggesting the robust of this device.