Growth and optoelectronic properties of polymorphous silicon thin films

Polymorphous silicon is a nanostructured thin film consisting of a small fraction of nanocrystalline silicon particles and/or clusters embedded in a relaxed amorphous matrix. This heterogeneous material is produced under plasma conditions close to powder formation. The hydrogen bonding in this material was probed by infrared absorption and hydrogen evolution measurements. Surprisingly, the heterogeneous nature of the microstructure has no deleterious effect on the electronic and transport properties of these films; rather the transport and the hole transport in particular are better than those of standard amorphous silicon. These properties suggest polymorphous silicon is an excellent alternative to amorphous silicon. The performance and stability of the material and solar cells are discussed in terms of the hydrogen bonding structures as well as the preparation conditions used to produce the material. The obtaining of highly stable wide gap single junction polymorphous silicon solar cells suggests that polymorphous films are well adapted for the top cell in tandem or triple junction devices.