Analytical modeling of p-i-n solar cells constitutes a practical tool to extract material and device parameters from fits to experimental data, and to establish optimization criteria. This paper proposes a model for p-i-n solar cells based on a new approximation, which estimates the electric field taking into account interface potential drops at the intrinsic-to-doped interfaces. This leads to a closed-form current/voltage equation that shows very good agreement with device simulations, revealing that the inclusion of the interface potential drops constitutes a major correction to the classical uniform-field approach. Furthermore, the model is able to fit experimental current/voltage curves of efficient nanocrystalline Si and microcrystalline Si p-i-n solar cells under illumination and in the dark, obtaining material parameters such as mobility-lifetime product, built-in voltage, or surface recombination velocity. Copyright © 2012 John Wiley & Sons, Ltd.