Synergistic experimental and theoretical investigation of carbazole–cyanopyridine-based hole-transporting materials

Abstract

This work highlights the design, synthesis, and characterization of three new hole-transporting materials (DJ01-alkyl, PR01-alkyl, and PM01-alkyl) based on donor–acceptor–donor (D–A–D) and acceptor–acceptor–donor (A–A–D) concepts. Crystals of two compounds, DJ01-alkyl and PR01-alkyl, were obtained under similar crystallization conditions. The molecular structures were thoroughly examined using DFT, photophysical, electrochemical, and thermal methods. The UV-vis absorption spectrum of DJ01-alkyl displayed a significant bathochromic effect compared to its counterparts PR01-alkyl and PM01-alkyl. This could be because the thiophene units enhance conjugation and lead to a bathochromic shift. Compared to DJ01-alkyl (1.7 × 10⁻⁵ cm² V⁻¹ s⁻¹) and PM01-alkyl (1.6 × 10⁻⁵ cm² V⁻¹ s⁻¹), PR01-alkyl was found to have a higher hole mobility value of 2.1 × 10⁻⁵ cm² V⁻¹ s⁻¹. To further explain and complement the experimental data, DFT calculations of the geometry, electronic structure, absorption, reorganization energy, transition density matrix, and density of states of compounds were performed. These characteristics make it abundantly evident that compounds based on carbazoles and cyanopyridines are very attractive materials for use as hole-transporting materials in perovskite solar cells.