Theory and analysis of temperature coefficient of open-circuit voltage (dVOC/dT) in heterojunction solar cells

Performance of solar cells and modules at operating temperature relative to standard test conditions is primarily determined by the temperature dependence of V_OC. Usually this dependence is analyzed by applying a simplistic semi-analytical equation to experimental data without complete understanding of the underlying mechanisms that affect the temperature coefficient dV_OC/dT (V_OC'). Unanswered questions related to the temperature dependence include: separating the contribution of interface vs. absorber recombination towards V_OC', temperature coefficient comparison of homojunction vs. heterojunction silicon solar cells, and dependence of V_OC' on inversion strength in heterojunction cells. We derive an analytical equation that provides the explicit dependence of V_OC' on the material parameters and the strength of recombination. The role of recombination in different regions of the cell is exemplified by comparing two CuInGaSe devices with different bandgaps.