Optimizing Charge Transport Properties of Dithieno[3,2-b:2',3'-d] Pyrrole-Based Hole Transport Materials for Perovskite Solar Cells: a DFT Study.

Abstract

Designing novel hole-transporting materials with optimal electronic properties, efficient charge mobility, and good processability is essential to advancing the performance of perovskite solar cells (PSCs). In this study, we report the rational design and quantum chemical investigation of a series of pyrrole-based small molecules (H16-A to H16-H) employing a donor-π-acceptor (D-π-A) configuration. The molecular scheme features a pyrrole core and dimethoxy triphenylamine (DMTPA) donor, bridged via a benzene linker and different electron-acceptor groups. The density functional theory (DFT) results demonstrated that designed HTMs have stabilized HOMO energy levels (-5.01 to -5.19 eV), low HOMO-LUMO energy gap (0.81 to 1.84 eV), less optical absorption on the visible region ([Formula: see text] ≤ 390 nm), and superior solubility compared with the reference molecule (H16). The low binding energy (E_b) and high light harvesting efficiency (LHE) indicated that designed HTMs have higher photocurrent flow ability. A series of charge transfer parameters related to excited state properties including charge transfer distance (D_index), amount of charge transfer (q^CT), t-index, H-index, hole-electron overlap (S_±), and inter fragment charge transfer (IFCT) were computed. Moreover, low reorganization energy (0.2780 to 0.3066 eV), high hole-hopping rate (~ ×10¹² s^-1), larger transfer integrals (0.3083 to 0.3551 eV), and higher total amount of charge transfer revealed that designed HTMs have effective hole transport ability for PSC. The outstanding performance of molecules H16-A to H16-H highlights their strong potential as promising candidates for the development of high-efficiency perovskite solar cells, with prospective applications in future commercial photovoltaic technologies.