Impact of the p+ layer on current-voltage characteristics of Cu(In,Ga)Se2-based solar cells.

Cu(In,Ga)Se2-based solar cells often exhibit fill factor losses at low temperature, in particular after red illumination or reverse biasing. A narrow p+ layer between the absorber and buffer layers is commonly assumed to explain these effects. In this contribution, we analyze by means of analytical and numeric models the influence of the parameters of the p+ layer on current-voltage characteristics. Specifically, we find expressions linking the voltage at which the deterioration of the current-voltage curve begins with the acceptor density and the width of the p+ layer. Moreover, we derive formulas describing the height of the barrier in the conduction band caused by the p+ layer. Examples of the analysis of simulated current-voltage characteristics using our approach are presented. Based on the voltage at which the decrease of the current starts, it is possible to estimate the upper and lower limits of the density of the acceptors in the p+ layer. Furthermore, we analyze the relationship between the fill factor and the height of the barrier in the conduction band, which is determined by the density of acceptors in the p+ layer. [ABSTRACT FROM AUTHOR]