THE PERFORMANCE AND STABILITY OF AMBIENT-TEMPERATURE MOLTEN-SALTS FORSOLAR-CELL APPLICATIONS

Room temperature molten salt systems based on methyl-hexyl-imidazolium iodide (MHImI) have been used to scrutinize the performance character istics, the stability and the mass-transfer effects in a photoelectroc hemical regenerative device, as the latter is influenced and can even be limited by local concentration and mass-transport of the electroact ive redox mediator species in the electrolyte phase. These salts appea r to afford particular advantages over organic liquids as solvents for solar cell electrolytes. Cell performance showed outstanding stabilit y, with an estimated sensitizer turnover in excess of 50 million. An i nvestigation has been carried out on the physical-electrochemical prop erties of MHImI and its mixtures with organic solvents such as n-methy l-oxazolidinone, acetonitrile and with other lower viscosity molten sa lts such as methyl-butyl-imidazolium triflate. The repercussions of th ese properties on solar cells is described experimentally by the perfo rmance of practical application devices. Simulation models of mass tra nsport in the nanocrystalline solar cell help illustrate operational a spects such as concentration profiles, limiting currents, anticipated mass-transfer overpotential as a function of current density, and they help to make projections as to how the properties of molten salt elec trolytes can be better exploited toward this practical end.