Unravelling the potential for dithienopyrrole sensitizers in dye-sensitized solar cells

Two D-π-A dyes based on the dithieno[3,2-b:2′,3′-d]pyrrole π-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.