Comparison of Dye- and Semiconductor-Sensitized Porous Nanocrystalline Liquid Junction Solar Cells

The liquid junction dye-sensitized solar cell (DSSC) has reached laboratory solar efficiencies of 11%. In contrast, the semiconductor-sensitized analogue (SSSC) has, up to now, exhibited a maximum efficiency of 2.8%. This begs the questions: is this difference fundamental? Will SSSCs always be inferior to DSSCs? We discuss the differences between the two types of cells, considering typical charge transfer times for the various current generating and recombination processes. Three main factors that could contribute to differences between the two types of cells are discussed: multiple layers of absorbing semiconductor on the oxide, the different electrolytes normally used for the two types of cell, and charge traps in the absorbing semiconductor. Entropic effects and the irreversible electron injecting nature of the normally used Ru dye to TiO2 are also briefly considered. We conclude that although the DSSC does possess some fundamental advantages, we can expect large improvements in efficiency of the SSSC, possibly reaching values comparable to the DSSC.