Temperature dependent electroluminescence and voltages of multi-junction solar cells

The spectral electroluminescene (EL) of a monolithic triple-junction solar cell reveals the sub cell open circuit voltages under variation of temperature and carrier concentration. We present an EL-setup which is able to acquire a full spectrum in less than 10 seconds and give insight into the voltage-extraction process. The sum of the sub cell voltages is in excellent agreement to open circuit voltages acquired under concentrated illumination. The temperature induced voltage losses are investigated and explained by a bandgap dependent increase in intrinsic carrier concentration. Finally, the accurate extraction of the sub cell bandgaps helps to identify a temperature rise with increasing current density.