Abstract
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.
Highlights
Lifetime is one of the most important solar cell parameter that determines short-circuit current Isc, open-circuit voltage V oc, efficiency η et al There are some methods to get the lifetime of minority carriers
One dimension numerical calculation was used to simulate the evolution of distribution of carriers during time resolved photoluminescence (TRPL) measurement
The calculation results suggest both intensities of light and lifetimes of minority carriers influence TRPL curves
Summary
By changing the output power of laser, radiative recombination and non-radiative recombination could he separated They used single exponential decay function to fit the TRPL, and it is appropriate due to the nanostructure InP is uniform. Homo-junction solar cells are more common, and the band bending of a homo-junction solar cell lies in the middle instead of the front of corresponding layer, which is different from heterojunction ones. There is no such simulation result on TRPL in a homojunction solar cell to the author’s knowledge. In this paper, based on 1D numerical calculation, the TRPL curve of GaAs is simulated, and the effect of non-uniform doping is discussed. For tri-junction GaInP/GaAs/Ge solar cells, the degradation is mainly attributed to change of minority carrier lifetime in middle GaAs sub-cells.[23,24] In this paper, we would use TRPL and PL to get Kτ of GaAs in a GaInP/GaAs/Ge solar cell
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