In this work, we discuss a new fundamental PID mechanism that has not been reported. We developed in-situ Kelvin probe force microscopy to monitor the potential evolution at nanometer scale under high-voltage stress. We observed large-area junction degradation during the stressing and junction recovery by heat treatment from the same location. Electron-beam induced current (EBIC) results support the large-area damage, which has a much lower collected current (dark region) and has an abrupt transition between the bright and dark areas, in addition to local shunts. Transmission electron microscopy does not find stacking faults in the dark-EBIC region. Furthermore, time-of-flight secondary-ion mass spectrometry indicates that the large-area damage correlates with more sodium content. The consistent results shed new light on PID mechanisms that are essentially different from the widely reported local-junction shunts.

A new potential-induced degradation (PID) mechanism for c-Si is reported. Multiple characterization techniques 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, are combined. All results point consistently to a new discovery: substantial large-area deterioration of materials and junctions plays a major role.

We discuss results of our investigations toward understanding bulk and surface components of light-induced degradation (LID) in low-Fe c-Si solar cells. The bulk effects, arising from boron-oxygen defects, are determined by comparing degradation of cell parameters and their thermal recovery, with that of the minority-carrier lifetime (964;) in sister wafers. We found that the recovery of 964; in wafers takes a much longer annealing time compared to that of the cell. We also show that cells having SiN:H coating experience a surface degradation (ascribed to surface recombination). The surface LID is seen as an increase in the q/2kT component of the dark saturation current (J02). The surface LID does not recover fully upon annealing and is attributed to degradation of the SiN:H-Si interface. This behavior is also exhibited by mc-Si cells that have very low oxygen content and do not show any bulk degradation.

Bifacial photovoltaic (PV) modules are able to utilize light from both sides and can therefore significantly increase the electric yield of PV power plants, thus reducing the cost and improving profitability. Bifacial PV technology has a huge potential to reach a major market share, in particular when considering utility scale PV plants. Accordingly, bifacial PV is currently attracting increasing attention from involved engineers, scientists and investors.