Range of loss mechanisms accessible by illuminated lock in thermography (ILIT)

Illuminated Lock-In Thermography (ILIT) was introduced as a further development of Dark Lock-In Thermography (DLIT) in 2004 and allows to measure under conditions considerably closer to real operation conditions of solar cells. Recently, a number of different modes were developed, that differ in the measurement conditions chosen. This contribution investigates favorable measurement conditions for the most important parameters of a solar cell. It will be shown that adapted modes of Lock-In Thermography are well suited for the investigation of linear and non-linear shunts, bulk material quality and losses due to series resistance as e.g. contact resistance and inappropriate metalization patterns. Bulk material quality is best investigated under open circuit conditions (V(ind oc)-ILIT), whereas series resistance problems dominate the Thermography image under short circuit conditions (J(ind SC)-ILIT). Shunts on the other hand tend to dominated the measurement at intermediate to high voltages, thus offering the possibility to distinguish between losses due to shunting and due to series resistance. Finally, good agreement between contact resistance images obtained by J(ind SC)-ILIT and emitter potential maps obtained by Corescan is demonstrated.