New Redox Mediators for Quantum Dot Sensitized Solar Cells

Quantum dot sensitized solar cell (QDSSC) performance has more than doubled in just 3 years of research. However, one remaining limiting factor is the redox mediator electrolyte that completes the circuit by transferring electrons from the counter electrode to the photoanode. Optimum redox mediators must efficiently reduce II-VI semiconductor quantum dots (CdS/CdSe), while maintaining redox potentials sufficiently positive (>0.3 V vs NHE) to realize open circuit voltages higher than the state-of -the-art QDSSCs. A series of Mn complexes have been developed that meet both requirements. Open circuit voltages around 1V have been achieved, much higher than the 0.6V currently obtained with the common sulfide/polysulfide redox mediator. The efficiency increased approximately 50% above equivalent cells made with a cobalt trisbipyridine redox mediator.