Analyses of current-voltage characteristics of Cu2ZnSn(S,Se)(4)-based solar cells reveal a non-superposition between dark and illuminated curves. Numerical simulations have been carried out to model the behavior of the Cu2ZnSn(S,Se)(4)/CdS heterojunction, and to extract from experimental data the minority carrier diffusion length in the absorber. A small value of 200 nm has been found, which induces collection losses in the absorber and is therefore a limiting factor to achieve high power conversion efficiencies. Additional experimental results, such as irradiance dependent photovoltaic properties and voltage dependent external quantum efficiency, are also presented and simulated with the same model. This confirms the validity of our approach and reveals interesting effects in Cu2ZnSn(S,Se)(4)-based solar cells. (C) 2014 Elsevier B.V. All rights reserved.