Influences of surface contaminating elements on potential-induced degradation of crystalline silicon solar cells

Effects of alkali metal on the potential-induced degradation (PID) phenomena in wafer-based conventional p-type crystalline silicon technologies were studied. It is known that sodium rapidly and severely brings the shunting-type PID (PID-s) phenomenon; however, the impact of other alkali metal such as lithium and potassium on the PID-s phenomenon is unrevealed. We used solar cells that light-receiving surface was contaminated with lithium, sodium or potassium, and in order to control the sodium content, prepared were photovoltaic modules without cover glass and performed were PID tests and anneal tests. During the tests, the performance of each module was judged by the current-voltage measurements and the electroluminescence images. After a certain time of PID tests, the secondary ion mass spectrometry analysis was performed on the solar cells of some modules. Thus, the penetration status of alkali metal elements is judged. From the PID tests and anneal tests, we conclude that, the negative potential of the solar cell light-receiving surface is the basis of the PID-s phenomenon. Furthermore, in the PID tests, all elements penetrated into the solar cell, but only sodium rapidly causes severe PID-s phenomenon. The PID-s phenomenon appears to be moderated when both lithium and sodium are present on the solar cell light-receiving surface. Therefore, we believe that lithium and potassium do not cause PID-s phenomenon, and lithium seems to mitigate the sodium-induced PID-s phenomenon.