Rational Design of Dithienopicenocarbazole-Based Dyes and a Prediction of Their Energy-Conversion Efficiency Characteristics for Dye-Sensitized Solar Cells

A series of metal-free organic donor–acceptor (D–A) derivatives (<b>ME01</b>–<b>ME06</b>) of the known dye <b>C281</b> were designed using first-principles calculations in order to evaluate their potential for applications in dye-sensitized solar cells (DSSCs). Their physical and electronic properties were calculated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). These include molecular properties that are required to assess the feasibility of a dye to function in DSSCs: UV–vis absorption spectra, light-harvesting efficiency (LHE), and driving forces of electron injection (<i>Δ<i>G</i></i>_inj). <b>ME01</b>, <b>ME02</b>, and <b>ME04</b> are predicted to exhibit broad absorption optical spectra that cover the entire visible range, rendering these three dyes promising DSSC prospects. Device-relevant calculations on these three short-listed dyes and the parent dye <b>C281</b> were then performed, whereupon the dye molecules were adsorbed onto anatase TiO₂ surfaces to form the DSSC working electrode. Associated DSSC device characteristics of this dye···TiO₂ interfacial structure were determined. These include the light-harvesting efficiency, the number of injected electrons, the electron-injection lifetime, and the quantum-energy alignment of the adsorbed dye molecule to that of its device components. In turn, these calculated parameters enabled the derivation of the DSSC device performance parameters: short-circuit current density, <i>J</i>_SC, incident photon-to-electron conversion efficiency, IPCE, and open-circuit voltage, <i>V</i>_OC. Thus, we demonstrate a systematic <i>ab initio</i> approach to screen rationally designed D–A dyes with respect to their potential applicability in high-performance DSSC devices