Device parameters such as series and shunt resistances, saturation current and diode ideality factor influence the behaviour of the current-voltage (I-V) characteristics of solar cells and photovoltaic modules. It is necessary to determine these parameters since performance parameters are derived from the I-V curve and information provided by the device parameters are useful in analyzing performance losses. This contribution presents device parameters of CuIn(Se,S)(2)- and Cu(In,Ga)(Se,S)(2)-based solar cells, as well as, CuInSe(2), mono- and multicrystalline silicon modules determined using a parameter extraction routine that employs Particle Swarm Optimization. The device parameters of the CuIn(Se,S)(2)- and Cu(In,Ga)(Se,S)(2)-based solar cells show that the contribution of recombination mechanisms exhibited by high saturation current when coupled with the effects of parasitic resistances result in lower maximum power and conversion efficiency. Device parameters of photovoltaic modules extracted from I-V characteristics obtained at higher temperature show increased saturation current. The extracted values also reflect the adverse effect of temperature on parasitic resistances. The parameters extracted from I-V curves offer an understanding of the different mechanisms involved in the operation of the devices. The parameter extraction routine utilized in this study is a useful tool in determining the device parameters which reveal the mechanisms affecting device performance. (C) 2010 Elsevier Ltd. All rights reserved.