Defect Analysis of Monolithic GaInP/GaInAs/Ge Triple-Junction Solar Cells by Luminescence Technology

The luminescence of solar cell gives unique signatures of the bandgap and cell composition. Electroluminescence (EL) and photoluminescence (PL) of the monolithic GaInP/GaInAs/Ge triple-junction solar cells are investigated to probe each subcell quality. The band-to-band emissions from the GaInP, GaInAs, and Ge junctions are observed at the wavelengths of 0.7, 0.9, and 1.8 μm, respectively. The emission from tunneling junction and defects are also characterized. By adjusting the excitation wavelength, PL spectra can probe individual subcell. EL spectra can measure the spectral uniformity and defect level of individual subcell with selected filter. PL and EL mapping with selected filter corresponding to relative emission wavelength range can help to determine the uniformity, defect, and hot spots of individual layer. The PL and EL emission are related to absorption edge and the temperature coefficient can be used to design the current match condition at operation temperature. PL complementary to EQE measurement can give a quick look of the current matching for cell design. The in-line PL application can also be a real-time diagnostic tool for quality control and yield enhancement.