Absolute Electroluminescence Imaging Diagnosis of GaAs Thin-Film Solar Cells

A spatially resolved absolute electroluminescence (EL) imaging method was utilized to analyze the photovoltaic properties and resistive loss properties of a GaAs thin-film solar cell. TheI–Vrelation was extrapolated from the absolute EL efficiency measurements in conjunction with the external-quantum-efficiency (EQE) measurements; the EL extrapolatedI–Vrelation has a merit over the conventionalI–Vrelation measured with a solar simulator that it could eliminate the series resistance effect caused by external probe contact. Then, the mapping of the internal voltage of the solar cell and the sheet resistance of the window layer of the solar cell were obtained from the calibrated absolute EL imaging method. Finally, optic electroconversion losses of the solar cell including radiative loss, nonradiative loss, thermalization loss, transmission loss, and junction loss were quantified given by the EL and EQE measurements.