Impact of alkali doping on carrier transport in Cu2ZnSn(S, Se)4 thin films for solar cell applications

Abstract

The effects of alkali doping (Na, Li, K) on the carrier transport in Cu2ZnSn(S, Se)4 (CZTSSe) thin films have been studied systematically using time-resolved THz spectroscopy. Na and Li doping seem to have no influence on the carrier mobility, whereas K doping leads to a noticeable decrease. In addition, we found that Na doping increases the lifetime of photocarriers, but Li and K doping do not. Consequently, we are able to evaluate the diffusion length of photocarriers as a function of the alkali dopants. This result provides a helpful orientation for future efforts to improve the performance of CZTSSe-based solar cells.