A Molecular-Level Exploration of Dopant-Free Pyrazine-Derived Hole Transport Materials: Investigation of Interfacial Interaction in Perovskite Photovoltaics

The development of innovative core structures and peripheral groups for organic hole-transporting materials (HTMs) continues to be a focal point in enhancing the performance of perovskite solar cells (PVSCs). This study reports the design and synthesis of dopant-free pyrazine-based HTMs. PS1 features a D–A–D type structure with pyrazine as the acceptor and 4,4′-dimethoxy triphenylamine (4,4′-OMe-TPA) as the donor, while PS2 adopts a D–π–A–π–D configuration with an additional thiophene unit as π-spacer along with 4,4′-OMe-TPA as donor. Both compounds are synthesized through a simple two-step synthetic procedure. These HTMs are subjected to structural, photophysical, electrochemical, theoretical, and photoelectrochemical studies with an emphasis on evaluation of structure–property relationships. Theoretical studies are conducted to explore the electronic distribution, optimized molecular structure, and frontier molecular orbitals. Their performance in PVSCs is systematically evaluated without adding dopants. PS2 exhibits superior photoluminescence quenching compared to PS1, indicating more efficient charge transfer from the perovskite layer. Notably, PS2 achieves a power conversion efficiency (PCE) of 11.9%, surpassing the performance of PS1 (PCE of 10.15%). These findings highlight the potential of adjusting the electron-deficient core and π-bridge units as an effective strategy to optimize the properties of HTMs and improve their performance in PVSC applications.