Characterization of the interface properties in a-Si : H/c-Si heterostructures by photoluminescence

Abstract

Photoluminescence measurements on hydrogenated amorphous silicon/crystalline silicon (a-Si : H/c-Si) heterostructures have been used for two aspects of their characterization: the monitoring of the crystalline silicon wafers and of their interface properties after different steps of solar cell processing and the tracking of interface properties on purpose-built symmetrical structures with different amorphous silicon overlayers. The difference in the quasi-Fermi level splittings in these symmetrical structures, determined both experimentally and by numerical modelling, suggests an energetic position of the interface defect distribution with a peak at around 0.7–0.8 eV above the c-Si valence band edge. Numerical modelling is also applied to the structures after solar cell processing steps and consistently tracks the variation in quasi-Fermi level splitting, i.e. excess carrier densities, in the c-Si layer. The agreement in the experimental and simulated open-circuit voltages for the final cell adds confidence to the interface defect parameters determined.