Characterization of Interface Recombination Velocity in GaAs/InGaP Heterojunction Solar Cells Using Dark Curve Measurements

In this article, a method for obtaining the interface recombination velocity in a solar cell from a measurement of the dark curve is presented. The front interface recombination S$_f$ between window and emitter of a GaAs-InGaP heterojunction cell passivated by an AlInP window is used to demonstrate the method. By choosing a proper emitter thickness, the equation for the dark saturation current J$_01$ reduces to two terms, one related to the bulk recombination and the other to the interface recombination. The growth direction (either upright or inverted) is found to have a huge influence on S$_f$ as a result of the formation of an interfacial layer in the inverted grown cells. It is also shown that S$_f$ and, therefore, the optimum cell design strongly depend on the emitter doping level. Using the obtained S$_f$ data, an optimized cell configuration on the substrate and in a thin film has been calculated, leading to a 1% (absolute).