Simulation of non-linear recombination of charge carriers in sensitized nanocrystalline solar cells

Abstract

Electron transport and recombination in electrolyte-filled sensitized nanocrystalline solar cell was investigated using Monte-Carlo simulation. Multiple-trapping in an exponential tail of trap states was used as an electron transport model. For simulation of the recombination, a new approach based on Marcus theory of charge transfer was developed and utilized to simulate both linear and non-linear (trap-assisted) recombination of electrons with holes in the electrolyte. Monte-Carlo simulation results, based on this approach, reproduced the non-constant diffusion length, recently observed in several experimental works. All simulation results were compared with theoretical predictions of the Marcus theory of charge transfer. Based on this comparison, interestingly it was found that random walk electron lifetime is different from the one which is obtained experimentally by small-perturbation techniques. This result is similar to the well-known Darken equation that describes the difference between jump and chemical diffusion coefficient. An interpretation based on the transport-limited recombination picture was provided to describe this result. These simulations establish a clear picture that describes how the localized trap states contribute to the recombination, leading to the non-linear recombination kinetics in sensitized solar cells.