Electro-analytical investigation of potential induced degradation in mc-silicon solar cells: case of sodium ion induced inductive loop

Potential induced degradation of the shunt type (PID-s) in multi-crystalline silicon (mc-Si) solar cells is becoming critical for performance reduction of solar panels in large scale photovoltaic (PV) power plants. In this article PID-s has been investigated by applying high voltage stress on mc-Si solar cells for their degradation and recovery and results have been explained on the basis of DC and AC characterization. The efficiency decreases drastically from 15.7% to 2.9% due to a high voltage stress of -800 V at 85 °C for 48 hours, which is attributed to a reduction in shunt resistance and an increase in depletion and diffusion capacitances. The reduction in electrical performance due to PID-s has been further explained by morphological, structural and elemental analysis. Observed negative capacitance behaviour in impedance spectra of mc-Si solar cells after PID-s has been attributed to structural deformation caused by potential induced migration of sodium ions (Na+) into mc-Si. The structural deformation induced by potential induced migration of Na+ ions has been confirmed by using non-destructive and lattice strain sensitive micro-Raman spectroscopy. The obtained experimental results have been correlated with existing theoretical understanding of p-n junction solar cells to explain the consequences of PID-s.