Effect of bridging group configuration on photophysical and photovoltaic performance in dye-sensitized solar cells

Abstract

Three new metal-free organic sensitizers with a D–A–π–A configuration based on a triarylamine donor, 2,1,3-benzothiadiazole (BTD) and different π units have been synthesized. Because a long alkyl side chain has been attached to the thiophene adjacent to BDT, HECA achieves the best performance. Under standard global AM 1.5 solar light conditions, the HECA based-device gives the best conversion efficiency of 9.13% with a J_sc of 16.14 mA cm⁻², a V_oc of 0.72 V and a FF of 0.77. Although EDCA displays superior optical properties, it does not give the desired results. The device based on EDCA achieves efficiency of 7.37% with a J_sc of 15.56 mA cm⁻², a V_oc of 0.67 V and a FF of 0.70. EIS analysis confirms the existence of fast recombination in the EDCA system. Further computational analysis indicates that the coplanarity and the very strong affinity to iodine molecules of EDCA may be the origin of the low performance.