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 VOC. 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 dVOC/dT (VOC'). Unanswered questions related to the temperature dependence include: separating the contribution of interface vs. absorber recombination towards VOC', temperature coefficient comparison of homojunction vs. heterojunction silicon solar cells, and dependence of VOC' on inversion strength in heterojunction cells. We derive an analytical equation that provides the explicit dependence of VOC' 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.