Less-understood phenomena in the light-induced degradation and photocarrier capture in a-Si:H

Abstract Light-induced degradation is studied in a variety of a-Si:H films and a-Si:H based solar cells. Photocarrier capture properties into the light-induced defects (LIDs) vary greatly with the temperature during light exposure and with sample microstructure. Capture into defects is likely to be governed by their surrounding local structure (nearby H atoms, carrier traps, clusters of traps), and depends on their thermal stability. Less-stable defects are created independently from more stable ones and their annealing modifies the distribution of deep gap states. The commonly observed non-unique relation between photoconductive properties and defect concentration, as well as apparent lack of correlation between film and solar cell degradation can be explained by systematic variations in defect capture coefficients (CC) with their thermal stability and sample preparation technique. Films deposited at the lowest plasma electron temperature, e.g. using high frequency and H-dilution exhibit the smallest capture into the LIDs.