Molecular engineering of novel dithiophene-fused hole-transporting materials for highly efficient perovskite solar cells

Understanding the relationship between structure and property of hole-transporting materials (HTMs) plays an important role in developing highly efficient perovskite solar cells (PSCs). Herein, we report a density functional theory study (DFT) combined with Marcus theory on the structural, electronic, optical, electrochemical and hole-transporting properties of designed molecules. The calculated results demonstrate that extending π-conjuration of the center by replacing CDT with IDT can lower the HOMO level, increase Stokes shift, enhance the solubility, strengthen the defect passivation ability and improve the hole mobility of molecules. The HOMO and LUMO energy alignments of the designed molecules properly match with the VBM and CBM of conventional perovskite CH3NH3PbI3 or mixed perovskite (FAPbI3)0.85(CH3NH3PbBr3)0.15, respectively. The introduction of electron-accepting groups in the π-linker results in the blue-shift of absorption edge into the UV region, which has no competition with the absorption of perovskites. Besides possessing lower HOMO levels, better solubilities and spectral properties, three designed molecules para-IDT-CN (1.76 × 10−1 cm2 V−1 s−1), meta-IDT-O (2.09 × 10−2 cm2 V−1 s−1) and meta-IDT-CN (7.53 × 10−3 cm2 V−1 s−1) exhibit higher hole mobility than the reported HTMs CDT (4.15 × 10−3 cm2 V−1 s−1) and CDT-CN (1.15 × 10−3 cm2 V−1 s−1), which ensures that these novel molecules have potentials to be efficient HTMs in the application of PSCs.