Phenoxazine-Type Pigments from Pycnoporus sanguineus as ZnTiO3/TiO2 Sensitizers for DSSCs.

Dye-sensitized solar cells (DSSCs) using natural pigments offer a low-cost, non-toxic alternative to ruthenium dyes, but fungal sensitizers remain underexplored relative to plant-derived pigments. This study reports, for the first time, the phenoxazine pigments cinnabarin and cinnabaric acid from Pycnoporus sanguineus extract (PSE) as DSSC sensitizers, paired with a ZnTiO3/TiO2 heterojunction photoanode designed to suppress interfacial recombination. The extract was characterized by HPLC-DAD and FTIR, and the semiconductors ZnTiO3/TiO2 (ZTO) and TiO2 (TO) by XRD and SEM. Four device configurations (TO, PSE/TO, ZTO/TO, PSE/ZTO/TO) were evaluated photovoltaically and compared statistically (ANOVA, Tukey/Duncan), while DFT calculations (Gaussian, VASP) modeled dye electronic structure, band-edge alignment, and surface adsorption. Efficiency increased significantly across all configurations, from 0.06% (TO) to 0.38% (PSE/ZTO/TO). Band-alignment calculations revealed a thermodynamically favorable injection pathway from the dyes into ZnTiO3, with TiO2 acting as a unidirectional barrier against backtransfer, consistent with the dye-independent increase in open-circuit voltage observed experimentally. Adsorption modeling revealed a shared vertical anchoring geometry with differentiated surface selectivity between the two dyes. These results establish P. sanguineus phenoxazines as a competitive, mechanistically characterized addition to the limited catalog of fungal DSSC sensitizers and support ZnTiO3/TiO2 heterostructure engineering as a key strategy for improving fungal-pigment DSSC performance.