Enhancing the efficiency and stability of perovskite solar cells by incorporating CdS and Cd(SCN2H4)2Cl2 into the CH3NH3PbI3 active layer

Abstract

To improve the charge separation and transport efficiency in perovskite solar cells (PSCs) with a TiO₂-based hybrid mesoscopic/planar architecture, CdS and Cd(SCN₂H₄)₂Cl₂ are incorporated into the CH₃NH₃PbI₃ active layer through in situ synthesis to prepare CdS:Cd(SCN₂H₄)₂Cl₂:CH₃NH₃PbI₃ bulk-heterojunction films for PSCs. The incorporated CdS and Cd(SCN₂H₄)₂Cl₂ improve the quality of perovskite films. Moreover, Cd(SCN₂H₄)₂Cl₂ can effectively reduce the defect state density on the CH₃NH₃PbI₃ crystal surface, which decreases charge recombination and facilitates charge transport in PSCs. Furthermore, first-principles calculations show that the I atom of CH₃NH₃PbI₃ has a strong interaction with the Cd atom of CdS, which induces interfacial charge redistribution and charge transfer at the CH₃NH₃PbI₃/CdS interface and therefore decreases the energy of the CH₃NH₃PbI₃:CdS composite system, leading to more efficient electron–hole separation and improved structural stability of the perovskite bulk-heterojunction film. For the above reasons, the CdS:Cd(SCN₂H₄)₂Cl₂:CH₃NH₃PbI₃ bulk-heterojunction cell shows much higher efficiency and better stability than the PSCs with pure CH₃NH₃PbI₃. The highest efficiency reaches 20.1%, which is 1.16 times that (17.3%) of the PSCs with pure CH₃NH₃PbI₃ and is also much higher than those of previously reported CH₃NH₃PbI₃ PSCs with a compact/mesoporous TiO₂ film. Our research results may provide a new understanding for improving the structural stability and performance of PSCs.