Large-Area Material and Junction Damage in c-Si Solar Cells by Potential-Induced Degradation

This paper reports a new potential-induced degradation (PID) mechanism for crystalline silicon (c–Si), where Na diffuses everywhere and causes large-area material and junction degradation with point defects. Multiple characterization techniques are combined—Kelvin probe force microscopy, electron-beam induced current, dark lock-in thermography, transmission electron microscopy, time-of-flight secondary-ion mass spectrometry, and microwave photoconductance decay—as well as density functional theory (DFT) calculations. These characterization techniques and theoretical calculations are complementary in various aspects of a material's chemical, structural, electrical, and optoelectrical nature, as well as in atomic, nanometer, micrometer, millimeter, and cell and module scales. All results point consistently to a new discovery: substantial large-area deterioration of materials and junctions play a major role in c–Si PID (in addition to the previously reported local shunting defect caused by Na diffusion to planar defects). This new finding reveals a key PID component and leads to a new strategy for tailoring c–Si photovoltaics to ultimately resolve the PID issue.