Molecular Design and Optoelectronic Investigations of Phenothiazine D-A-π-A DyeSensitizers Using DFT/TD-DFT Method for Potential Solar Cell Application

Renewable energy, like solar energy, has become a viable solution to the scarcity, environmental degradation, and greenhouse effects of fossil fuels. Many technology companies are developing reliable and affordable sustainable energy technology to convert sunlight into electricity and reduce greenhouse gas emissions and nuclear by-products. In this research, eight metal -free organic phenothiazine and phenoxazine-based dyes of the D-A-pi-A architecture were studied theoretically using DFT and TD-DFT techniques for use as dye -sensitized solar cells (DSSCs). The effects of pi-spacers on the structural, electrical, photovoltaic, and optical characteristics of the designed dyes were examined. The results showed that 2-[3-(10 H -phenoxazin-3-yl)furan-2-yl]-10 H -phenoxazine (PO) dyes have lower band gaps (Delta Eg) than 2-[3-(10 H -phenothiazin-3-yl)furan-2-yl]-10 H -phenothiazine (PZ) dyes, which means 2-[3-(10 H -phenoxazin-3-yl)furan-2-yl]-10 H - phenoxazine pushed electrons towards the acceptor unit readily than 2-[3-(10 H -phenothiazin-3-yl)furan-2-yl]-10 H -phenothiazine. And that thieno[3,4-b]pyrazine contributed to the lowering of band gaps (Delta Eg) than thieno[3,2-b]thiophene, thus enhancing the photoelectronic properties of the dyes. The dyes' band gaps Delta Eg ranged from 1.48 to 1.88 eV; open -circuit voltage ( V-OC ) values ranged from 0.60 to 0.98 eV, and light -harvesting efficiency (LHE) values ranged from 0.6583 to 0.9444. Phenoxazin-3-yl-furan-2-yl-10 H -phenoxazine- thieno[3,4-b][1,4]dioxine-thieno[3,4-b]pyrazine dye (PODB), phenoxazin-3-yl-furan-2-yl-10 H -phenoxazine-thieno[3,4-b][1,4]dthiine- thieno[3,4-b]pyrazine dye (POTB), and phenothiazin-3-yl-furan-2-yl-10 H -phenothiazine-thieno[3,4-b]dioxine-thieno[3,2-b]thiophene dye (PZDT) were identified as the most suitable candidates for DSSC applications based on molecular, optical, and most photovoltaic parameters.