Theoretical Investigation on Interfacial-Potential-Limited Diffusion and Recombination in Dye-Sensitized Solar Cells

Abstract

The electron diffusion and recombination limited by interfacial potential in dye-sensitized solar cells are theoretically investigated within a potential barrier model. The dependence of diffusion coefficient D and recombination rate K on various parameters is examined. The D and K exhibit electron density dependence with three distinct regions: (i) constant region, (ii) linear region, and (iii) nonlinear region when the quasi-Fermi energy level sweeps from the lower-energy side to the conduction band edge. For a dye-sensitized solar cell operated at normal conditions, a linear-density-dependent expression for D or K is a reasonable approximation. The diffusion coefficient D in a temperature range of 200–400 K exhibits thermally excited behavior as D ∼ exp(−Eact/kBT) when the potential barrier width W is large enough (∼4 nm) and the corresponding activation energy Eact is independent of quasi-Fermi energy level or electron density. The diffusion coefficient D shows linear dependence on particle size. The ...