Molecular engineering and synthesis of novel metal-free organic sensitizers with D-pi-A-pi-A architecture for DSSC applications: The effect of the anchoring group

Herein, we report the design and synthesis of two metal-free organic sensitizers (MR-5 & MR-6) with a D-pi-A-pi-A architecture based on a trimethoxy benzene donor core carrying two different withdrawing/anchoring groups including cyanoacetic acid and rhodanine-3-acetic acid via thiophene as a pi-spacer. Benzothiadiazole was incorporated as a strong auxiliary electron acceptor, which greatly improved the molar extinction coefficient and electronic coupling across the molecular diameter of the dyes. The optical and electrochemical properties of the two dyes were investigated. The photovoltaic studies revealed that MR-5 anchored with cyanoacetic acid showed significantly greater light harvesting (IPCE), which resulted in improved PCE with better photovoltaic parameters than MR-6. MR-5 achieved the higher total solar-to-electric conversion efficiency of 6.03% and showed an IPCE of 65% at 420 nm. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to study equilibrium molecular geometries, frontier molecular orbitals, vertical electronic excitations, and the theoretical data were consistent with experimental results.