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 (ME01–ME06) of the known dye C281 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 (ΔGinj). ME01, ME02, and ME04 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 C281 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, JSC, incident photon-to-electron conversion efficiency, IPCE, and open-circuit voltage, VOC. Thus, we demonstrate a systematic ab initio approach to screen rationally designed D–A dyes with respect to their potential applicability in high-performance DSSC devices.