Electrodeposition of Silicon from Nonaqueous Solvents

A study of the electrodeposition (ED) of silicon from silicon halides in a nonaqueous electrolyte solution is described. In spite of the use of nonoxidizing electrolytes, the electrodeposits usually become oxidized on air exposure. In similarity to other work, it is postulated that this is due to the deposit being formed with a spongy or honeycombed morphology. However, secondary neutral mass spectrometry (SNMS) and X-ray diffraction (XRD) analyses show that a region of the deposit close to the substrate has sufficient purity for semiconductor properties. This is verified by observing diode behavior at junctions of the deposited layers and mercury contacts. For deposition on crystal silicon substrates, it proved possible to form a p-doped ED-Si/c-Si heterojunction which showed a solar cell conversion efficiency of 1.8%. This is probably the first photovoltaic cell which uses electrodeposited silicon in a heterojunction.