Investigation of defects generated during the epitaxial lift-off process in a flexible GaAs solar cell

We have to investigate the optical and the electrical properties of flexible GaAs solar cells fabricated by using the epitaxial lift-off (ELO) process. Used the photoluminescence (PL) and J-V measurements. The as-grown GaAs solar cells were transferred onto Au/polyimide (ELO-layer/Au; ELA) and polydimethylsiloxane (PDMS) (ELO-layer/PDMS; ELP) flexible substrates. At 300 K, we observed PL emission bands caused by defects below the GaAs band edge transition energy (1.425 eV) for both the ELA and the ELP samples. The PL intensities for the ELA and the ELP samples, which were due to the defects in those samples, were higher than that for the as-grown sample. Moreover, the interference effect due to the internal multireflection (IMR) of PL light is lead that the PL peak by the defects is observed as the PL with several peaks. The PL intensity of the ELA sample was enhanced by the reflection effect at the GaAs/Au interface. In the J-V characteristics, the short-circuit current density and the efficiency of ELA sample were reduced by about 2.13 mA/cm² and 1.7%, respectively, compared to the corresponding values for the GaAs-ref sample, because photo-generated carriers were trapped by the defect states generated during the ELO process.