Quantitative analysis of the influence of shunts in solar cells by means of lock-in thermography

Abstract

Infrared lock-in thermography not only allows one to image shunts very sensitively in all kinds of solar cells, but also to measure dark currents flowing in certain regions of the cell quantitatively. After dealing with the physical basics of quantitative lock-in thermography, three types of measurements are described: 1. the quantitative measurement of the I-V characteristic of a point shunt, 2. the evaluation of the influence of shunts on the efficiency of a cell as a function of the illumination intensity, and 3. the mapping of the ideality factor n and the saturation current density J/sub 0/ over the whole cell. The investigation of a typical multicrystalline solar cell shows that the shunts are deteriorating predominantly the low light level performance of the cell, and that crystal defect related variations of the injection current density are predominantly caused by a variation of J/sub 0/ rather than of n.