Microcrystalline silicon and ‘micromorph’ tandem solar cells

The case for thin-film silicon as one of the main future options for cost-effective photovoltaic solar cells is outlined. The limitations of present amorphous silicon (a-Si:H) solar cells are briefly mentioned. Hydrogenated microcrystalline silicon (μc-Si:H) deposited by PECVD (plasma-enhanced chemical vapor deposition) at low substrate temperatures (approx. 200 °C) constitutes a new and additional possibility for solar cells. Properties of intrinsic μc-Si:H layers deposited by PECVD at VHF (very high frequency) excitation frequencies are listed, together with the necessary conditions for obtaining device-grade material. Performances obtained so far with μc-Si:H solar cells are given; the latter are compared with estimated limits for pn- and pin-type devices with Eg = 1.1 eV. Finally, present performances and future perspectives for 'micromorph' (μc-Si:H/a-Si:H) tandem solar cells are discussed. © 2002 Elsevier Science B.V. All rights reserved.