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

Abstract

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.

Side‐Chain Methylthio‐Based Position Isomerism of Hole‐Transport Materials for Perovskite Solar Cells: From Theoretical Simulation to Experimental Characterization

“…[28] The details of the synthesis can be found in the supporting information. The chemical structures of RQ4-RQ6 were confirmed by 1 H NMR 13 C NMR and HRMS characterization (Figures S4-S12, Supporting Information). The electrochemical properties of RQ4-RQ6 in DCM solution were measured by cyclic voltammetry (CV).…”

“…The ground state structures of RQ4-RQ6 were optimized at B3P86/6-311G (d,p) level, as shown in Figure S1 (Supporting Information) . [13] As can be indicated from the Figure S1 (Supporting Information) that the dihedral angles between the methylphenylsulfide units and the carbazole core for RQ4, RQ5, and RQ6 are 14.60, 12.70, and 9.05°, respectively. [14] A relatively smaller angle for RQ6 exhibits a better planar configuration, which may be beneficial to improve the intermolecular ππ stacking and results in a higher hole mobility than RQ4 and RQ5.…”

“…In ESP, the stability of the materials is mainly evaluated by the degree of negative charges. [13] For the RQ6 in ESP, it seems that the degree of negative charges (blue color) are less than these of RQ4 and RQ5. The stability of RQ6 should be better than that of RQ4 and RQ5.…”

“…Molecule of RQ6 with higher v h than that of RQ4 and RQ5 is probably due to its more compact crystal stack compared to RQ4 and RQ5. [13,16,22] As shown in Figure S2 (Supporting Information), the crystal volumes of RQ4-RQ6 are 2259.46, 2349.77, and 2249.84 nm 3 , respectively. In the isomers, the smaller crystal volumes may be beneficial in promoting the ππ stacking, allowing for higher v and thus improved k ij and ultimately greater u h .…”

“…In the isomers, the smaller crystal volumes may be beneficial in promoting the ππ stacking, allowing for higher v and thus improved k ij and ultimately greater u h . [10c, 13,23] It is very important for HTMs with good hole mobility. However, effective charge-transfer at perovskite/HTMs interface is a precondition for realizing the photoelectric conversion of the PSC devices.…”