Damage to passivation contact in silicon heterojunction solar cells by ITO sputtering under various plasma excitation modes

Abstract

Analysis of damage to passivation contact in heterojunction with intrinsic thin layer (HIT) solar cells by indium tin oxide (ITO) sputtering under various plasma excitation modes such as radio frequency (RF), direct current (DC), RF-superimposed DC, pulsed DC is presented. A significant degradation of effective minority carrier lifetime of the precursor cells at both low and high-level injections after the ITO deposition by sputtering technique was observed regardless of plasma excitation modes. We found that the main reason for this degradation was mainly due to the ion flux in the sputtering plasma rather than the ion kinetic energy. On the basis of the experimental and simulated results, we attributed the degradation of surface passivation quality mainly to the damage of the amorphous-silicon/crystalline-silicon interfaces rather than that of the intrinsic hydrogenated amorphous silicon layers. This degradation could be significantly reduced by the ITO deposition at a high temperature in which a trade-off between degradation and curing step was expected to occur. The cell performance of the HIT solar cells using the ITO films deposited by various plasma excitation modes at 180 °C was subsequently discussed. The ITO films deposited by the RF-superimposed DC mode exhibited a high potential as excellent opto-electrical properties and free sputter-induced damage electrodes for HIT solar cell applications. To our best knowledge, this is the first time that the ITO films deposited by the RF-superimpose DC mode are used as electrodes in the HIT solar cells.