Transient Electrical Characteristics of Silicon Heterojunction Solar Cells under Fast Transient Illumination

Abstract

For vehicle integrated photovoltaics (VIPV) there are possibly specific requirements on the speed of maximum power point tracking. However, a certain delay in the response of solar cells to fast irradiance changes might impact those requirements on the MPPT. The subject of this work is therefore the investigation of the transient electrical behaviour of state-of-the-art silicon heteroj unction solar cells. We use a fast switchable LED-array and an oscilloscope to investigate the cell voltage of silicon heterojunction solar cells under transient illumination. We find that these cells have a switch-off delay that is smaller than one millisecond when operated at or close to the maximum power point. This can be assumed to be faster than the time scale on that irradiances change typically occur on a car body while driving. We also find that, after switching off the light source, the transient cell voltage does not show a simple capacitive behaviour, but a more complex characteristic. A theoretical analysis shows that this behaviour can be explained by the nonlinear dependency of the diffusion and depletion capacitance and the minority carrier lifetime on the cell voltage.