Study of Thermal Fatigue of Soldered Photovoltaic Cells by Thermal Resistance Measurement

摘要

The solder layers used to attach concentrator photovoltaic cells to electrical leads and heat sink substrates have experienced failure after various periods of thermal cycling. In order to determine the degree of solder joint failure as a function of temperature and time, a study was initiated to measure the degree of solder debonding after a schedule of controlled thermal cycles. The cells were Sandia First Generation baseline cells assembled by G.E. as shown in Fig. 1. The degree of debonding was determined by measuring the thermal resistance of the cell-substrate-heat sink stack using a testing device constructed at Sandia Labs as shown in Fig. 2. The cell contributions to the stack resistance are shown in Table I. The thermal resistance was determined by measuring the cell temperature rise resulting from the passage of a large DC electrical current through the cell. The temperature rise was determined by first calibrating the dark forward voltage of the cell as a function of temperature and then measuring the change in this voltage as a function of time after the removal of the electrical heating current. (ERA citation 09:005854)