The purpose of this work was to build a numerical model of thermally activated tunneling transport by upgrading the drift-diffusion transport model in one-dimensional semiconductor simulator ASPIN, and to identify the current limiting mechanisms of the CIS monograin layer solar cells. The superposition of the classical drift-diffusion transport and the semi-classical thermionic-field transport is applied across the whole solar cell structure. The implemented model correctly predicts the shapes of temperature dependent current density-voltage characteristics and the temperature dependence of the photogenerated current density at the short-circuit condition in the range from 320 K down to 160 K. (C) 2007 Elsevier Ltd. All rights reserved.