Energy Level Tuning of Novel Star-Shaped D-π-D-A-Based Metal-Free Organic Dyes for Solar Cell Application

A novel concept of D-pi-D-A organic sensitizer as a replacement for traditional D-pi-A ones is proposed. Remarkably, the incorporated hybrid unit of hexyloxy- substituted dyes reveals several promising characteristics in the areas of light-harvesting and efficiency owing to the following: (i) inclusion of pi-spacer over customary design reveals the bathochromic shift of absorption spectra and enhancing molar extinction with LUMO energy gap reduction; (ii) energy level tuning was achieved by donor side modification with succinct alkyl-substituted dye (DM) and protracted alkyl-substituted dye (DH) and reveals the low bandgap and enhances electron transport of TiO2/dye/electrolyte interface. Meticulous investigation of photophysical, photoelectrochemical, and theoretical properties and performance of DSSCs is described. In particular, the experimental and theoretical parameters of aforesaid dyes are well close to each other, revealing the power conversion efficiencies of DH and DM dyes as eta = 3.12%, J(sc) = 6.68 mA/cm(2), V-oc = 0.73 (V) and eta = 1.69%, J(sc) = 3.60 mA/cm(2), V-oc = 0.70 (V), respectively. Furthermore, the enhanced performance of DH is attributed toward high molar extinction coefficient, high charge recombination resistance, very low charge transfer resistance, and high excited-state electron lifetime compared to the DM dye. To the best of our knowledge, D-pi-D-A type molecular engineering is an ideal shape for the enhancement of photocurrent efficiency in DSSCs sectors.