Power conversion efficiency (PCE) is one of the important factors in influencing the overall performance of dye-sensitized solar cells (DSSCs), and precise prediction of PCE is a feasible strategy for preparing highly efficient DSSCs devices. In this work, we designed a series of phenothiazine-based organic dyes by introducing different π-spacers including the 4-isopropyl-4H-dithieno­[3,2-b:2′,3′-d]­pyrrole (DTP) and 2,7-dihydronaphtho­[1,2-d:5,6-d′]­diimidazole (NDI) to tune their photovoltaic properties. The present studies reveal that the PCE value of the DTP-based dye is estimated to be 8.55%, in excellent agreement with the experimentally available value (8.19%) observed in the reported analogue. In comparison to DTP, the strong electron-deficiency NDI group induces a remarkable red-shifting of maximum absorption band, broadening the optical absorption into the near-infrared region. As a consequence, the NDI-based dye achieves an impressive PCE value of 15.51%, which is expected to be a potential organic dye applied in DSSCs.

Studies demonstrate that our designed dyes 3 and 4 exhibit broad optical absorption in the 550–650 nm region and high photoelectric conversion efficiencies of over 32%.

The electrical and optical properties of four T-shaped (D)2–A−π–A organic dyes, 3-(5-(1,4-bis­(4-(diphenylamino)­phenyl)-6-methyl-6H-indolo­[3,2-b]­quinoxalin-8-yl)­furan-2-yl)-2-cyanoacrylic acid (1), 3-(5-(1,4-bis­(4-(diphenylamino)­phenyl)-6-methyl-6H-indolo­[3,2-b]­azaquinoxalin-8-yl)­furan-2-yl)-2-cyanoacrylic acid (2), 2-(5-(4,10-bis­(4-(diphenylamino)­phenyl)-5-methyl-5H-[1,2,5]­thiadiazolo­[3,4-b]­carbazol-7-yl)­furan-2-yl)-2-cyanoacrylic acid (3), and 3-(5-(4,10-bis­(4-(diphenylamino)­phenyl)-5-methyl-5H-[1,2,5]­oxadiazolo­[3,4-b]­carbazol-7-yl)­furan-2-yl)-2-cyanoacrylic acid (4) with triphenylamine as donor, furan as the π group, cyanoacrylic acid as acceptor, as well as different ancillary acceptors, are theoretically investigated by multiscale simulations. On the basis of the isolated dyes, the frontier molecular orbital, the Fürster resonance energy transfer, and absorption spectra are studied to explore the effect of different ancillary acceptors. After that, the dye–TiO2-adsorbed system is considered by first principle. On the basis of the adsorbed system, the accurate values of short-circuit current density, open-circuit voltage, and power conversion efficiency are calculated, which is helpful to distinguish various dyes. It is always a perplexing problem for previous theoretical studies. Additionally, the aggregation effect is also considered to evaluate the performance of the dyes. 6-Methyl-6H-indolo­[3,2-b]­azaquinoxaline and 5-methyl-5H-[1,2,5]­oxadiazolo­[3,4-b]­carbazole are testified to be suitable auxiliary acceptors. On comparing the D−π–A dye with the same donor, the π group, and acceptor, it is established that the insertion of the ancillary acceptor is important to improve the overall performance.

Numerous organic dyes have been developed for dye-sensitized solar cells (DSSCs). However, theoretical screening has not played a due role in designing new dyes. It is mainly attributed that there is rarely quantitative calculation and the inaccurate estimated values for short-circuit current density (J SC) and open-circuit photovoltage (V OC), especially for V OC. In this work, V OC is theoretically predicted by two different models for three D−π–A organic dyes (1, 2, and 3) with the same π bridge and acceptor as well as different donors. Although there is a slight deviation in their structures, their properties are successfully differentiated by accurate quantitative calculations. Dimethoxybenzene-substituted indoline is more suitable as donor than methoxy-substituted triphenylamine and methyl-substituted indoline when it combines with 8H-thieno [2′,3′:4,5]­thieno­[3,2-b]­thieno­[2,3-d]­pyrrole (TTP) as π bridge and cyanoacrylic acid as acceptor. The properties of the donor are not only related to the core group but are also determined by the substituted group. A less than 10% deviation between theoretical and experimental results is an assurance to perform a reasonable prediction for photocurrent–photovoltage.

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