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

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.