Accessing externally induced spatially-resolved strain in GaAs thin-film solar cells by electroluminescence imaging

Externally induced strain effect was investigated in GaAs thin-film solar cells by electroluminescence (EL) imaging method. The strained regions demonstrated not only enhancement of local EL intensity but also redshift of the EL emission peaks. The observations were explained well by a gradient quantum-well (GQW) model correlated with tensile strain in the GaAs thin films. External biaxial strain was considered in this model which was accordingly obtained from the energy shift of the EL spectra. Finally, the spatially resolved strain in GaAs thin-film solar cells was obtained from the EL images by relating the EL emission intensity to the shift of the EL spectra. This work provides a potential standard method for diagnosis of externally induced strain in thin-film solar cells by EL measurements.