Reducing energy disorder by stabilizing octahedral lattice with thiocyanate for efficient and stable Sn-Pb mixed perovskite solar cells

The easily generated energy disorder within Sn-Pb perovskite due to the oxidation of Sn2+ into Sn4+ could lead to enhanced Urbach energy (EU) and severe nonradiative energy loss. Here, we reveal the degradation mechanism of Sn-Pb mixed perovskite films under light/O2 and only O2 conditions as well as the relationship between perovskite degradation and energy disorder. Furthermore, we develop an energy disorder regulation strategy of using NH4SCN as an additive for Sn-Pb perovskite films, which exists at grain boundaries to promote the carrier transport effectively and suppress the oxidation of Sn2+. Beneficial from the coordination of SCN– with under-coordinated Sn2+ and Pb2+, the octahedral structure is well stabilized and it largely reduces the Urbach energy and energy disorder in Sn-Pb perovskite. As a result, the 5% NH4SCN treated Sn-Pb mixed perovskite solar cells achieve a power conversion efficiency of 21.48%. The unencapsulated devices retained 87% of their initial PCE in the N2 atmosphere after 200 h of maximum power point tracking.