Investigating Charge-Carrier Dynamics in Heteroatom-Functionalized Triphenylamine Hole Transport Materials for...

Enhancing the efficiency and long-term stability of perovskite solar cells (PSCs) critically depends on the development of high-performance hole-transporting materials (HTMs). In this study, a novel series of thienothiophene-based small organic molecules (IF1-IF10) were designed and investigated as potential HTMs through end-capped molecular modification of a synthetic reference molecule, IF-R [5-((3,6-bis(4-(bis(4-methoxyphenyl)amino)-phenyl)thieno[3,2-b]thiophen-2-yl)methylene)-3-ethyl-2-thioxothiazolidin-4-one]. A comprehensive quantum chemical analyses were performed using density functional theory (DFT) and time-dependent (TD-DFT) at the MPW1PW91/6-31G (d, p) level to investigate their optical and optoelectronic characteristics. The study encompassed evaluations of frontier molecular orbitals, absorption spectra, light-harvesting efficiency, charge-transfer properties, transition density matrices, hole and electron reorganization energies, density of states, natural population analysis, and photovoltaic performance parameters, including measurements of open-circuit voltage and fill factor. Compared to the synthetic reference IF-R molecule, which exhibits an energy gap of 2.59 eV and absorption maximum at 437.58 nm, the designed IF1-IF10 compounds show significantly reduced band gaps and red-shifted absorption peaks in dichloromethane, indicating enhanced light-harvesting capabilities. Among them, IF-7 emerged as the most promising candidate, featuring a narrow band gap of 1.12 eV, strong absorption (807.93 nm), and the highest open-circuit voltage (0.98 V). This work demonstrates that strategic end-group modifications of thienothiophene-core HTMs offer a powerful design pathway to optimize optoelectronic performance. The promising results for IF-7, in particular, underscore the potential of this molecular engineering approach to advance the next generation of efficient and stable PSC devices.