Synthesis and computational study of coumarin thiophene-based D-π-A azo bridge colorants for DSSC and NLOphoric application

This article is comprised of designing and synthesis of three coumarin-based donors (D)-pi-azo-acceptor (A) colorants with -COOH and -SO3H anchoring groups for application in dye-sensitized solar cell (DSSC). Prototype DSSC devices were prepared with these colorants as sensitizers and were characterized through IV and EIS measurements to explore the practical performance. The well-performing colorant NAA 236 exhibit a short-circuit current density, J(sc) of similar to 10.28 mA cm(-2), with an open-circuit voltage, V-oc of similar to 0.62 V. The electro-chemical impedance spectroscopy (EIS) and electron lifetime (tau(e)) analysis showed effective performance with R-rec (141.61 Omega) and tau(e)10.5 ms for the NAA 236 colorant respectively. The power conversion efficiency (PCE) of 4.5 % (AM 1.5 G, 100 mW cm(-2)) is achieved for NAA 236 that has the - COOH (an anchoring group) at the para position of the azo group with fill factor FF of similar to 68.7. Theoretical Density Functional Theory (DFT) and Time-Dependent TD-DFT calculations were performed using the method B3LYP/6-311 + g(d,p). The HOMO-LUMO energy, vertical excitation energy, Global Reactivity Descriptors (GRD) i.e. electrophilicity index (omega), hyperhardness(F) and Light-harvesting efficiency (LHE) property were assessed through optimized geometry, and it showed a linear trend with Power Conversion Efficiency (PCE). All the sensitizers demonstrate excellent nonlinear optical (NLO) response and display a direct relation with photovoltaic performance.