When paired with alternate redox electrolytes, structural modifications in dye molecules significantly influence photovoltaic performance under outdoor and indoor illuminations. The present study investigates two triphenylamine-based D–π–A dyes (L1 and SP-1), where L1 features an O-alkyl substitution on its triphenylamine donor. The impact of this peripheral modification on the electrochemical, photophysical, and photovoltaic properties was explored using asymmetric dual-species copper(II/I) redox electrolytes. Interfacial charge transfer dynamics were analysed to explain device performance across various lighting conditions. SP-1, with substituted peripheral O-alkyl chains, exhibited superior standalone power conversion efficiency (2.88%) compared to L1 (1.07%). However, when co-sensitized with XY1b, L1:XY1b achieved a higher PCE of 6.49%, outperforming SP-1:XY1b (5.44%) under one sun illumination and achieving comparable indoor photovoltaic power conversion efficiency (∼25%). These findings highlight the importance of precise structural tailoring in co-sensitized dyes for enhanced performance.
