Local voltage mapping of solar cells in the presence of localized radiative defects

Hyperspectral electroluminescence and photoluminescence imaging of photovoltaic materials and devices produces three-dimensional spatially and spectrally resolved luminescence data, which can be calibrated to an absolute scale, enabling the extraction of high resolution maps of quantities, such as the local voltage (quasi-Fermi-level splitting). This extraction requires supplemental measurements of external quantum efficiency (EQE), but these do not have the same spatial resolution. Previously, assumptions have been made to overcome this limitation. In this work, we evaluate these assumptions for InGaAs solar cells with significant spatial variation in the luminescence spectrum shape due to small regions with elevated concentrations of radiative defects. Although appropriate for small variations in the spectral shape, we find that with more significant variation, these assumptions can result in nonphysical EQEs and too-low voltages. Combining multiple methods can help to alleviate this, or a minimum voltage map can be extracted, which will be similar to the actual voltage when EQE is high. Published by AIP Publishing.

Automated summary

Hyperspectral electroluminescence and photoluminescence imaging of photovoltaic materials and devices can extract high-resolution maps of physical quantities, but require supplemental measurements for calibration. Assumptions made previously to overcome limitations may not be applicable in cases where significant spectral shape variation exists.