New camera model for absolute quantum efficiency measurements from electroluminescence of solar cells or modules

The external electroluminescent quantum efficiency EQELED of solar cells/modules and their open-circuit voltage Voc are directly linked to each other. Measurement of EQELED with a calibrated camera enables, therefore, quantitative determination of Voc. We present a camera calibration model emphasizing the identification and separation of linear and non-linear sensor regimes. To demonstrate the approach, a conventional low-cost digital consumer camera is modified to detect the infrared radiation emitted by electrically biased silicon solar modules. Modules spanning more than 45 years of technology are investigated: Voc ranges from approximately 560 mV for early modules from 1978 (efficiency ≈6%) up to 690 mV for state-of-the-art industrial modules (efficiency ≈21%). The corresponding EQELED ranges from 0.0007% to 0.2%. The model is not only applicable to electroluminescent but also to photoluminescent measurements.