Surface Modification in CsPb_0.5Sn_0.5I₂Br Inorganic Perovskite Solar Cells: Effects of Bifunctional Dipolar Molecules on Photovoltaic Performance

Inorganic tin-lead binary perovskites have piquedthe interestof researchers as effective absorbers for thermally stable solar cells.However, the nonradiative recombination originating from the surfaceundercoordinated Sn2+ cations and the energetic offsetsbetween different layers cause an excessive energy loss and deterioratethe perovskite device's performance. In this study, we investigatedtwo thioamide derivatives that differ only in the polar part connectedto their common benzene ring, namely, benzenecarbothioamide and 4-fluorophenylcarbothioamide(F-TBA). These two molecules were implemented as modifiers onto theinorganic tin-lead perovskite (CsPb0.5Sn0.5I2Br) surface in the perovskite solar cells. Modifiersthat carry C US and NH2 functional groups, equippedwith lone electron pairs, can autonomously associate with surfaceSn(2+) through coordination and electrostatic attractionmechanisms. This interaction serves effectively to passivate the surface.In addition, due to the permanent dipole moment of the intermediatelayer, an interfacial dipole field appears at the PCBM/CsPb0.5Sn0.5I2Br interface, reducing the electronextraction potential barrier. Consequently, the planar solar cellwith an ITO/PEDOT:PSS/CsPb0.5Sn0.5I2Br/PCBM/BCP/Ag layered structure featuring an F-TBA surface post-treatmentdemonstrated a noteworthy power conversion efficiency of 14.01%. Simultaneously,after being stored for 1000 h in an inert atmosphere glovebox, thenon-encapsulated CsPb(0.5)Sn(0.5)I(2)Brsolar cells managed to preserve 94% of their original efficiency.