Time resolved photoluminescence studies of degradation in GaInP/GaAs/Ge solar cells after 1MeV electron irradiation

Time resolved photoluminescence (TRPL) is a powerful method to character the behaviors of carriers as it has high time resolution that could reflect the reactions of carriers within nanoseconds. For solar cells, minority carrier lifetime is the most important parameter. TRPL has been used to measure the lifetime for uniform materials. However, for homojunction solar cells, doping distribution and carrier drift make the spectroscopy analysis much difficult. Thus one dimension numerical calculations are used to study the time-dependent photoluminescence (TRPL) decay of GaAs sub-cell in GaInP/GaAs/Ge solar cells. Calculation shows that both lifetime of minorities and light intensities could determine the line shape of TRPL. The bimolecular recombination under high injection modifies the curve from single-exponential to non-single-exponential one. For TRPL of homojunction solar cell, the photoluminescence decay process is not synchronized in all parts, and the decay is fast in emitter but slower in base regions. To get the lifetimes of minority carriers after 1MeV electron irradiation, carrier generation parameter G0 should be fitted by numerical method firstly. The damage factor Kτ=4.8×10-15 cm2/ns is fitted from TRPL results. Photoluminescence spectra (PL) are also used to get Kτ=5.5×10-15 cm2/ns which is similar with the value obtained from TRPL.