Comparison of amorphous silicon absorber materials: Kinetics of light-induced degradation
We investigate the inﬂuence of the deposition parameters for intrinsic amorphous silicon absorber layers on light-induced degradation (LID) of thin-ﬁlm silicon solar cells. The focus is on absorber layers with different bandgaps: on one side, solar cells with a wide-bandgap absorber layer that provides open-circuit voltages up to 1.04 V; on the other, cells with short-circuit current densities of 18.2 mA / cm2 with a 300-nm-thick narrow-bandgap absorber layer, and 20 mA / cm2 at reverse bias for a cell with a 1000-nm-thick absorber layer. Between these extremes, we varied the hydrogen-to-silane ratio and the deposition pressure during the absorber layer deposition. The light-induced degradation of these materials—covering the deposition regimes of low-pressure, protocrystalline, polymorphous, and high-pressure amorphous silicon—incorporated in single-junction amorphous silicon solar cells is detailed here. For each pressure, we found an optimum hydrogen dilu-tion with least LID close to the amorphous-to-microcrystalline transition. The relative LID is similar for all pressures at optimized hydrogen dilutions. Further, we present the inﬂuence of absorber layer thickness, p-layer thickness, and deposi-tion rate on the kinetics of light-induced degradation to facilitate the choice of a material for its application in several types of multi-junction thin-ﬁlm silicon solar cells. We show that the degradation kinetics depends, in semi-logarithmic scale, only weakly on time but more on deposition conditions.