Abstract
As reported, the power conversion efficiencies of photosensitized solar cells with the four natural dyes from Ixora floral (NDIXs) were less than 1%, resulting from poor absorption of light in the visible (Vis) and near infrared (NIR) regions. The four NDIXs are aurone (ND1), pelargonidin (ND2), cyanidin (ND3) and malvidin (ND4). In this work, the study was conducted to investigate the effect of hybridizing the four NDIXs with graphene quantum dots (GQDs). The four NDIXs were studied computationally at the DFT/TDDFT with B3LYP/CAM-B3LYP functionals and 6-31G(d,p)/LANL2DZ basis sets all with the C-PCM solvation model. All the calculated parameters preferred the GQD-NDIX nanocomposites (NCs). NCs have appropriate HOMO and LUMO energy levels, absorbed light in the Vis region with a much higher light harvesting efficiency (by a difference not less than 5%), and significantly improve the intramolecular charge transfer (IACT) property necessary for efficient electron injection. Among the three configurations of the possible adsorption systems of NCs on TiO2, the NCs adsorbed on TiO2 through a covalent interaction between the NDs and TiO2 and not by the GQD adsorbed on TiO2 were evident by comparing the adsorption energies of different adsorption systems (the difference is not less than 0.7 eV). The optical properties of isolated dyes/nanocomposites were compared and discussed, and the optical properties of TiO2 adsorbed systems were calculated and discussed. The nonlinear optical (NLO) properties were compared and proved to be significantly enhanced and thus the IACT abilities in the adsorbed systems. This work can be used as a useful source for developing GQD-NDIX photosensitizers as efficient visible light harvesters in DSSC applications.