Performance enhancement of catechin-graphene quantum dot nanocomposites functionalized with carboxyl and doped/decorated with boron towards dye-sensitized solar cell applications: DFT and TD-DFT calculations.

A photosensitizer plays a vital role in adjusting the optical and electrochemical properties that affect the performance of dye-sensitized solar cells (DSSCs). Therefore, it should meet critical requirements for efficient operation of DSSCs. This study proposes catechin, a natural compound, as a photosensitizer and modifies its properties through hybridization with graphene quantum dots (GQDs). Density functional theory (DFT) and time-dependent DFT methods were used to investigate the geometrical, optical, and electronic properties. Twelve nanocomposites of catechin attached to carboxylated/uncarboxylated GQD were designed. The GQD was further doped with central/terminal boron atom or decorated with boron groups (organo-borane, borinic, and boronic groups). The available experimental data of parent catechin was used to validate the elected functional and basis set. Through hybridization, the energy gap of catechin was significantly narrowed by 50.66-61.48%. Therefore, its absorption was shifted from the UV to the visible region which matches the solar spectrum. Also, increasing the absorption intensity led to high light-harvesting efficiency close to unity that can increase current generation. The energy levels of designed dye nanocomposites are appropriately aligned with the conduction band and redox potential, indicating the feasibility of electron injection and regeneration. The observed properties confirm that the reported materials exhibit characteristics of interest thus they could be promising candidates for applications in DSSCs.