The influence of the structural variations of the fused electron rich-electron deficient unit in the pi-spacer of A-D-pi-D-A organic dyes on the efficiency of dye-sensitized solar cells: A computational study

The present study aimed to evaluate a class of A-D-pi-D-A organic dyes by replacing central pi-spacer by fused electron rich(D) and electron deficient(A) moieties (D-A) with different configurations in order to shed light on the role of the structure of fused pi-bridge on the cell performance. In addition, the effect of the structure of side chain on the N-atom of donor was investigated. The electronic and optical properties of the dyes and dye-TiO2 complexes, which are relevant to the short circuit photocurrent density and open circuit photovoltage, were comprehensively analyzed. The results indicated that the correct choice of side chain results in improving V-oc while the molecular engineering of the side chain on the donor plays an insignificant effect on the electronic and optical properties of dyes. Further, the effect of the strength of auxiliary acceptor on the performance of dyes was evaluated. Based on the results, the pi-linkers including the moderate auxiliary acceptor with the DTP unit could improve intramolecular charge transfer parameters and the light harvesting efficiency, reduce the continuity multiple charge transfer pathways, and enhance electron injection to TiO2 semiconductor. The results can provide a helpful guidance to design high-performance di-anchoring dyes.