Tailoring electronic structure and charge transport in thiophene-based hole transport materials: An end-capping acceptor strategy for efficient perovskite solar cells

Abstract

Hole transport materials (HTMs) with suitable band alignment, robust charge mobility, and processability are highly desirable for the development of efficient perovskite solar cells. In this study, we determined the first principles-based structural, electrochemical, photophysical, stability, solubility, and charge transfer characteristics of five novel HTMs (Z26Z1–Z26Z5) obtained by thiophene-bridged terminal acceptor engineering of dimethoxythiophene-based Z26 HTM. Our findings showed that the newly designed HTMs exhibited effective coherence in terms of the excitation, diffusion, distribution, and transmission of charges, which are highly suitable properties for ultrafast hole mobility. The HTMs exhibited excellent band alignment with the perovskite material, thereby suggesting effective hole extraction and transport properties. Low absorption in the visible light region and larger Stokes shifts (91–104 nm) indicated the great flexibility and pore-filling attributes of our proposed HTMs, with suitable photophysical profiles. Ultrafast hole transport properties were also predicted based on the 35% smaller hole reorganization energy values compared with the reference HTM. In addition, analysis of the excitation states suggested that the HTMs exhibited uniform charge transmission, low charge coupling, and higher dissociation. Furthermore, the solvation free energy increased by a maximum of 51% in the designed HTMs, thereby enabling facile film fabrication and processability. Overall, our findings contribute to the understanding of HTM design methodologies for efficient optoelectronic properties. The proposed thiophene-based HTMs are strongly recommended to be incorporated into forthcoming perovskite solar cells to achieve higher efficiency.