Promising heterocyclic anchoring groups with superior adsorption stability and improved IPCE for high-efficiency noncarboxyl dye sensitized solar cells: A theoretical study

The strong adsorption stability and significantly improved incident photon-to-current conversion efficiency (IPCE) of the new anchoring group hydantoin moiety (HY) introduced into D-A-π-A dyes for dye sensitized solar cells (DSSCs), compared with the commonly used anchoring group cyanoacrylic acid (CA), were investigated through DFT/TD-DFT calculations on the [email protected](TiO2)48 interfacial electron dynamics for the first time. It is found that the dissociative bidentate bridging mode with a hydrogen bond is the most stable adsorption configuration on the TiO2 anatase (101) surface for HY-based dyes and could produce a dramatic increase in adsorption energy compared with that of CA-based dye. Energy decomposition analysis (EDA) was performed to elucidate the different adsorption energies for the different anchoring groups with different adsorption configurations. A simplified Tamm-Dancoff density functional theory approach (sTDA-DFT), proposed by Grimme, was used to calculate the excitation energy and oscillator strength of the sensitizers after adsorption. The calculated results indicate that the adsorption mode has significant effects on the absorption spectrum. In contrast to CA-based dye, HY-based dye exhibits comparable light harvesting ability after adsorption due to the combined effects of different adsorption configurations, although the isolated dye exhibits a blue-shifted absorption spectrum. It shows a similar electron injection and dye regeneration driving force, but the significantly larger coupling between the sensitizer and the semiconductor for HY-based dye is the main reason for its improved IPCE. Moreover, to further improve the light-harvesting ability of the dyes, two other heterocyclic groups, rhodanine (RD) and 2-(3-oxo-2,3-dihydroinden-1-ylidene)-malononitrile (MT), were introduced into the dyes as anchoring groups. The results show that dyes with the RD anchoring group exhibited significantly enhanced light harvesting ability with the red-shifted absorption spectrum, higher electron injection efficiency with larger electronic coupling and strong adsorption ability; thus, it is worthy of experimental synthesis for use in high-performance dye sensitized solar cells.