Analysis of the Temperature Dependence of the Open-Circuit Voltage

The influence of temperature on the open-circuit voltage (VOC) of crystalline silicon solar cells is analysed using different semiconductor temperature models with different levels of accuracy. The strongest influence besides the direct dependence of the intrinsic carrier concentration on temperature results from the temperature dependence of the band gap and the effective density of states, while the incomplete ionization plays a minor role for the implied voltage. However incomplete ionization can play an important role for the external voltage at temperatures below 50K due to imperfect selectivity of the emitter and back surface field. The observed saturation of VOC towards low temperatures is caused by the effective density of states. The temperature dependence from 80 K to 300 K and the intensity dependence as a function of temperature and illumination density were measured on a silicon wafer solar cell resulting in a maximum voltage of 1012 mV at T=85.8K. The measured values could be well described by theory.