Para-linked acceptor engineering unlocks high-efficiency phenothiazine dioxide hole transport materials for perovskite photovoltaics

Phenothiazine dioxide (PDO2)-based HTMs still suffer from limited charge-transport and suboptimal energy alignments, restricting the device performance substantially. In this work, we rationally designed and investigated five new phenothiazine dioxide-based derivatives (AH1–AH5) through para-linked end-cap acceptor engineering, employing density functional theory (DFT) at the B3LYP/6-31 G(d,p) level. The proposed design strategy is both crucial and innovative, as it employs a common phenothiazine dioxide spacer while systematically introducing advanced acceptor groups at the para-positions of the terminal rings, enabling precise control over optoelectronic properties. The structural modifications significantly tuned the optoelectronic and photovoltaic parameters, yielding optimized geometries, narrower band gaps (0.75–1.18 eV), and extended absorption in the Vis–NIR range (923–1014 nm). The designed molecules exhibited enhanced charge transfer, lower exciton binding energies, and improved dipole moments compared to the reference PDO2 molecule. Device-level simulations predicted remarkable improvements in photovoltaic parameters, with AH3 and AH4 molecules achieving power conversion efficiencies (PCEs) up to 20.3% and 18.4%, respectively (around 3 fold to the native reference R), alongside high open-circuit voltages (0.70–0.96 V) and fill factors exceeding 88%. These findings highlight that para-linked endcap engineered PDO2 derivatives are highly promising candidates for efficient and stable HTMs for next-generation PSCs, offering a cost-effective strategy and a robust design platform for future optoelectronic and photovoltaic applications.