Exploring the synergy between copper electrolytes and molecularly engineered thiocyanate-free cyclometalated ruthenium sensitizers for dye-sensitized solar cells.

Two novel cyclometalated ruthenium complexes, RC-4 and RC-5, featuring 1-phenylisoquinoline and phenyl quinazoline as ancillary ligands, respectively, were synthesized to investigate their viability with the environmentally friendly copper (Cu) redox mediator, [Cu(bpye)2]2+/+. The modification of the ligand environment resulted in variations in the energetics, photophysical properties, and photovoltaic performance of RC-4 and RC-5 sensitizers. Despite RC-5 sensitizer possessing a more positive ground state potential of 1.19 V versus the NHE, the RC-4 sensitizer, with a lower HOMO level of 0.72 V versus NHE, exhibited superior photovoltaic performance along with the Cu electrolyte, attributed to its enhanced light harvesting ability, improved lifetime and reduced back electron transfer, contributing to higher Jsc, Voc, and PCE.

Regulating Back Electron Transfer through Donor and π-Spacer Alterations in Benzothieno[3,2-b]indole-based Dye-sensitized Solar Cells.

Three metal-free organic D-π-A dyes with benzothieno[3,2-b]indole as electron donor, cyanoacrylic acid as both electron acceptor and anchoring group with benzene (BID-1), thiophene (BID-2) and furan (BID-3) as π-spacers were designed and synthesized for application in dye-sensitized solar cells (DSSCs). A planar and electron-rich heterocycle such as benzothieno[3,2-b]indole offers better backbone rigidity and improves charge transport properties in comparison to indolo[3,2-b]indole donor, previously reported from our group. Additionally, we synthesized a benzothieno[3,2-b]indole donor grafted with longer alkyl chains which efficiently prevented the approach of oxidized species in the electrolyte coming closer to semiconductor thereby arresting recombination. A power conversion efficiency of 4.11 % was achieved for dye-sensitized solar cells based on the furan π-spacer benzothieno[3,2-b]indole dye BID-3 in comparison to the corresponding indolo[3,2-b]indole dye (IID-3) having an efficiency of 1.71 %. Detailed interfacial electrical measurements along with theoretical calculations disclosed the mechanism of back electron transfer and improvement in photovoltaic performance with respect to variation in both donor and π-spacer.