Investigation of the Combination of Indoline and Naphthalimide in the Preparation of Photosensitizers for Photovoltaic Devices

Four dyes with substitutions of carbazole and phenothiazine in position C4 of naphthalimide were designed in conjugation as a donor–acceptor architecture (D–A). The absorption and emission characteristics of the prepared dyes were investigated in H₂O, dimethylformamide (DMF), and their mixture (DMF:H₂O = 1:1). The prepared dyes exhibited a pink and yellow color, with strong emission at λ_em = 526–590 nm due to charge transfer, with a positive solvatochromic effect. The feasibility of electron transfer in the dye-sensitized solar cell (DSSC) structure and energy levels were evaluated using electrochemical and density functional theory (DFT), which confirmed the use of dyes in the DSSC structure. The DSSCs were prepared using an individual strategy, and their optical properties were investigated under light of AM 1.5. The DSSCs based on dyes 1–4 achieved efficiency of 4.37%, 4.59%, 4.11%, and 4.27%, respectively. Therefore, the power efficiency increased by about 39% in the presence of the phenothiazine group.