Molecular doping with Phenyl-functionalized Triazatruxene as a Strategy for Trap Passivation in Perovskite Solar Absorbers

Abstract

Hybrid metal halide perovskite solar cells have rapidly achieved high efficiencies, positioning them as cost-effective candidates for next-generation photovoltaics. However, their inherently high defect density constrains their theoretical potential. Solution processing of hybrid metal halide perovskite absorbers enables optimization via additive engineering, where molecular additives can simultaneously passivate defects, refine the morphology, and improve their structural properties, ultimately enhancing the device performance. This study investigates the incorporation of p-type semiconducting triazatruxene derivatives—functionalized with either three phenyl (5,10,15-triphenyl-10,15-dihydro-5H-diindolo[3,2-a:3’,2’-c]carbazole, 3P-T) or three hexyl (5,10,15-trihexyl-10,15-dihydro-5H-diindolo[3,2-a:3’,2’-c]carbazole, 3H-T) groups—as dopants directly into the MAPbI₃ precursor solution. Even at very low concentrations (10⁻² mM), triazatruxenes dopants significantly influence the morphology, crystallinity, and electronic properties of the perovskite thin films. More importantly, our findings reveal that the phenyl-functionalized molecule induces a measurable defect passivation effect in the films, hindering any carrier recombination pathway aside from band-to-band transitions. This enhances charge carrier transport by reducing its activation energy, Ea, from 0.44 eV to 0.25 eV, thereby improving photocarrier separation and boosting the overall performance of Perovskite Solar Cells. Enhancements in photoluminescence, open-circuit voltage, and test cell efficiency further corroborate these effects. These insights highlight the potential of triazatruxene-based dopants for tuning perovskite film properties and advancing the performance of perovskite solar cells.