Automated characterisation of multi-junction thin film silicon solar cells

Accurate measurements and calibration of amorphous silicon and micromorph multi-junction solar cells poses a major challenge. Device measurements with commonly used single-lamp solar simulators can be associated with large uncertainties, as small changes in the simulator light can lead to significant non-linear differences in the current production of the device under test. To properly characterise multi-junction solar cells, a multi-source or spectrally adjustable solar simulator is required. This way, the spectral distribution of the simulator can be changed and stacked cells can be current matched. However, the methods available are somewhat slow, as they require the measurement of a quantum efficiency, and difficult to operate when done manually. This paper presents a method for automated characterisation of multi-junction and single-junction solar cells. Its key element is a fitting method for the spectral response from device measurements at different spectra. The automated approach is underlined with a simulated measurement of a double junction amorphous silicon cell. Simulations reflect the capabilities of the LED-based solar simulator prototype developed at CREST. Results show that the method is able to deliver high accuracy without the need for additional spectral response measurement systems or closely matched reference cells. Single- and multi-junction device calibration methods are briefly reviewed and the automated approach is described in detail including its potential error sources and requirements.