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.