Luminescent emission of multi-junction InGaP/InGaAs/Ge PV cells under high intensity irradiation

• Emission of InGaP/InGaAs/Ge under high intensity solar simulator was observed.
• The emission increases at higher concentration levels.
• The emission decreases at higher temperatures.
• Radiative recombination was observed at open-circuit conditions outdoors.

Combined electroluminescence (EL) and photoluminescence (PL) measurements were conducted in order to investigate the presence of luminescent emission of InGaP/InGaAs/Ge at different operating conditions of the tandem. Luminescent emission from cell samples was observed at different sun concentrations, voltage biases and temperatures. A high intensity pulsed solar simulator was used to photoexcite the device which exhibited strong radiative recombination from both the top InGaP and middle InGaAs junctions. Luminescent emission from the device was investigated under a range of voltage biases and was clearly observed at the maximum power point voltage of the sample under test indicating its presence during typical operating conditions of the solar cells. Investigation of the emission was also performed at relatively high temperatures (up to 60 °C) in order to mimic the outdoor operating conditions of a solar cell device. Luminescence was detected at high temperatures indicating that significant radiative recombination is present at even higher temperatures. Outdoor measurements under actual solar spectrum demonstrated the presence of luminescent emission in agreement with indoor testing. The significant amount of radiative recombination at the band-gap edges of the top junctions observed in our measurements gives evidence that optical coupling to the lower ones may occur. Finally, excitation power dependent PL was performed using monochromatic laser sources in order to investigate the impact of externally induced photocurrents of different intensity upon the radiative signal of each junction.