Non-uniform distribution in μc-Si1-xGex:H and its influence on thin film and device performance

In this work, hydrogenated microcrystalline silicon germanium (mu c-Si1-xGex:H) thin films were fabricated by plasma-enhanced chemical vapor deposition (PECVD) and developed as the infrared absorber for thin film silicon solar cells. Three kinds of the non-uniform distribution in mu c-Si1-xGex:H thin films including: the non-uniform distribution of Si and Ge, the non-uniform distribution of crystallization, and the non-uniform distribution of H, and how these affect the structural, optical and photoelectric properties of mu c-Si1-xGex:H thin films have been explored. The results show that the good film quality of mu c-Si1-xGex:H is associated with the low crystalline volume fraction and microstructure factor. The band gap of mu c-Si1-xGex:H is determined by the proportion of the Ge-related crystalline networks. In addition, it is suggested that the deterioration of the photosensitivity of mu c-Si1-xGex:H is mainly due to the increase of the Ge clusters with higher micro-void and defect density. Furthermore, by using mu c-Si1-xGex:H bottom sub-cells, the comparable efficiency can be realized under the thin thickness condition. An efficiency of 11.35% in an a-Si:H/a-Si0.6Ge0.5:H/mu c-Si0.5Ge0.5:H triple junction structure with total cell thickness as thin as 1200 nm was obtained. It is believed that the mu c-Si1-xGex:H thin films can be a better candidate for effective infrared absorber by further improving its microstructure uniformity. (C) 2016 Elsevier B.V. All rights reserved.