Abstract
The goals of RMG 1 is to perform calibration measurements of the short circuit current of reference solar cells under Standard Test Conditions (ISTC) and spectral response (SR) from at least two solar cells using the polychromatic SR method and to produce an uncertainty budget of the polychromatic method used at the facility at CREST, LU. The spectral responsivity and the spectra are essential for spectral mismatch and the uncertainty of the spectral mismatch for calibration of the ISTC. Hence PTB realized lowest measurement uncertainties for the calibration of ISTC of reference solar cells and serve as a qualified World Photovoltaic Scale (WPVS) laboratory. The facilities of PTB are based on the successfully applied Differential Spectral Responsivity (DSR) method that allows the determination of the absolute spectral responsivity and nonlinearity of solar cells with the lowest uncertainties. This method uses the combination of a modulated monochromatic beam and steady state white light (bias) sources. But the size of the calibrated solar cells is limited by the signal to noise ratio due to the power of the monochromatic beam. To solve this problem, a much stronger monochromatic light source would be necessary. The Loughborough University (LU) solves this problem with a workaround. The LU uses a polychromatic DSR facility to improve the signal to noise ratio. This is realized with a white light flasher and different optical filters. The spectral responsivity can be calculated with the knowledge of the polychromatic spectra and the related currents.
A set of three solar cells was investigated at PTB and LU. The research stay was used to transfer knowledge between the researcher and the guest organisation. The polychromatic method of LU can’t be finished, because the spectrometer was not working. A characterisation of selected components of the SR-facility at LU was performed. Instead of polychromatic method was a common calibration performed at LU, CREST.
Table 1: Results of the short-circuit currents under Standard Test Conditions (ISTC) with the DSR-facility at PTB and the PASAN 3b at LU. Also are the En-number (see equation (9)) shown for a conformity of both facilities. In a last step was Sample #1 used as reference solar cell.
| ID | PTB ISTC, PTB / mA | LU ISTC, LU / mA | En-number | LU ISTC, LU / mA with reference Sample #1 |
| Sample #1 | 141,11 ± 0,74 | 141,2 ± 3,9 | 0,03 | - |
| Sample #2 | 140,07 ± 0,74 | 140,3 ± 3,8 | 0,06 | 140,2 |
| Sample #3 | 35,70 ± 0,20 | (36,3 ± 1,0) | (0,59) | (36,2) |
The results of the common calibrations with the facilities at PTB and LU show a nearly perfect agreement. The En-numbers are less than 1 and very close to 0. This is a perfect agreement of both facilities.