Structural Engineering of FDT toward Promising Spiro-Typed Hole-Transporting Materials: Promoting the Hole Transport and Stabilizing the HOMO Levels

Design of a new spiro-typed core structure is one of the most important approaches for developing highly efficient hole-transporting materials (HTMs). In this work, the strategies of modifying with O/S heteroatoms and introducing a helical π-linker are evaluated based on the typical FDT molecule. Theoretical calculations show that all the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) of the studied HTMs are matched well with the energy band structure of perovskite, and the HOMO levels display a gradually negative-shifted trend from the FDT to SM30, which means that the favorable hole extraction and the easy interfacial energy regulation can be anticipated. Compared to the light absorption of the FDT, the absorption spectra of new tailored HTMs are slightly red-shifted. More importantly, our results indicate that introducing a helical π-linker and modification with heteroatoms in the spiro-typed core can be the effective methods to promote the hole transport ability of HTMs. Both the methods can effectually heighten the crystal stacking and intermolecular electronic couplings and further facilitate the hole transport of HTMs. Furthermore, the large Stokes shifts and the better solubility are also displayed for the newly tailored HTMs. In sum, this work provides useful insights for the design of highly efficient HTMs, and three new spiro-typed HTMs are proposed.