7,16-Dihydro-14H-diindolo[3,2-c:2,3-h]phenothiazine-based organic dyes with high molar extinction coefficient for efficient dye-sensitized solar cells

Two newly developed metal-free D-(-pi-A)2 dyes, WX1 and WX2, incorporating diindolophenothiazine (DIPZ) as an electron donor, were synthesized and employed in dye-sensitized solar cells (DSSCs). Notably, DIPZ was utilized for the first time in metal-free organic dyes. DIPZ, featuring the introduction of two benzopyrrole groups into the parent phenothiazine, extends the conjugated structure and demonstrates superior light harvesting capabilities compared to bare phenothiazine. Both WX1 and WX2 exhibited high molar extinction coefficients (up to 64,100 M-1 cm -1). Under standard global AM 1.5G solar light conditions, the WX1-sensitized solar cell achieved a higher power conversion efficiency (PCE) of 5.97 %, attributed to the enhanced molecular planarity facilitated by thiophene as the pi bridge. Additionally, to boost the photovoltaic performance of DSSCs, cosensitization with the reference dye WL8 resulted in WX2 attaining the highest PCE of 6.69 %, surpassing the individual efficiencies of WX2 and WL8. These findings underscore the efficacy of the DIPZ unit as an electron donor and highlight DIPZ-based organic dyes as promising candidates for efficient DSSCs.