Simple thiophene-bridged D–π–A type chromophores for DSSCs: a comprehensive study of their sensitization and co-sensitization properties

Herein, we report the design and synthesis of four new thiophene-bridged D–π–A configured organic dyes T1–4 comprising different donors, π-spacers and anchoring units, as potential sensitizers and co-sensitizers for DSSCs. The current work also highlights their structural, photophysical, thermal, electrochemical, theoretical, and photoelectrochemical studies, including evaluation of their structure–property relationships. The optical results revealed that the dyes T1–4 display λabs and λemi in the range of 402–461 nm and 556–575 nm, respectively, with a bandgap in the order of 2.31–2.58 eV. Furthermore, the results showed that the dyes possess all the pre-requisites to act as sensitizers/co-sensitizers. Among the tested dyes, the device based on sensitizer T2 achieved the highest PCE compared to the other three dyes, under the standard conditions. Furthermore, their co-sensitized devices were fabricated by co-adsorbing them with the well-known Ru-based MH-12 sensitizer and interestingly the co-sensitizer T3 carrying an alkoxy group and a barbituric acid anchor displayed the highest PCE of 8.79%, which is much higher than that of MH-12 alone (8.18%). Conclusively, the study furnishes a deeper understanding of the intricacies involved in the structural modification of sensitizers/co-sensitizers in achieving an enhanced performance of the devices.