Unravelling the Potential for Dithienopyrrole Sensitizers in Dye-Sensitized Solar Cells

Two D-pi-A dyes based on the dithieno[3,2-b:2',3'-d]pyrrole pi-bridge (DTP) were synthesized, characterized using UV-vis absorption spectroscopy and electrochemistry, modeled using quantum chemical calculations, and used as sensitizers in dye-sensitized solar cells (DSCs). The photoelectrochemical properties and DSC performance are thoroughly compared with their cyclopenta[1,2-b:5,4-b']dithiophene (CPDT) analogues. The use of DTP results in a small increase in the zero zero transition energy reflecting the higher lying lowest unoccupied molecular orbital that is commonly reported for DTP relative to CPDT systems. This increased optical gap manifests in slightly blue-shifted incident photon-to-collected electron conversion efficiency (IPCE) responses; however, increased open-circuit photovoltage values and improved charge-transfer kinetics relative to the CPDT systems result in comparable power conversion efficiencies. The present report highlights the potential of DTP for the development of tailored sensitizers employing stronger acceptors.