Unusual Lock-In Thermography Signals: Schottky-Type Grid Contacts, Peltier Effects, and Thermal Wave Interference

The technique of lock-in thermography (LIT) provides a number of well-established methods to image the lateral homogeneity of electrical parameters of solar cells. Using these methods, linear (ohmic) and nonlinear (diode-like) local leakage currents (edge currents, shunts), local Joule heating, and inhomogeneities of the series resistance and of the minority carrier lifetime can be imaged. However, in some cases, unusual LIT signals appear, which cannot be interpreted in the frame of generally accepted LIT methods. This contribution explains LIT signals connected with Schottky-type grid contacts, Peltier effects, and thermal wave interference, which is important to avoid any misinterpretation of LIT results