Polycrystalline silicon thin-film solar cells: Status and perspectives

The present article gives a summary of recent technological and scientific developments in the field of polycrystalline silicon (poly-Si) thin-film solar cells on foreign substrates. Cost-effective fabrication methods and cheap substrate materials make poly-Si thin-film solar cells promising candidates for photovoltaics. However, it is still the challenge for research and development to achieve the necessary high electrical material quality known from crystalline Si wafers on glass as a prerequisite to harvest the advantages of thin-film technologies. A wide variety of poly-Si thin-film solar cell approaches has been investigated in the past years, such as thermal solid phase crystallization - the only technology that had already been matured to industrial production so far - the seed layer concept where a large-grained seed layer is epitaxially thickened, direct growth of fine grained material, and liquid phase crystallization methods by laser or electron beam. In the first part of this paper, the status of these four different poly-Si thin-film solar cell concepts is summarized, by comparing the technological fabrication methods, as well as the structural and electrical, properties and solar cell performances of the respective materials. In the second part, three promising technologies are described in more detail due to their highly auspicious properties regarding material quality and throughput aspects during fabrication: (1) High-rate electron-beam evaporation of silicon for the low-cost deposition of high-quality material, (2) large-area periodic nano- and micro-structuring of poly-Si by the use of imprinted substrates providing a large absorption enhancement by a factor of six at a wavelength of 900 nm, (3) liquid-phase crystallization of silicon thinfilm solar cells by electron-beam, yielding an excellent poly-Si material quality reflected by an opencircuit voltage of 582 mV which has been achieved only very recently. A successful combination of these three complementary technologies is envisaged to be the basis for a prospective low-cost and highly efficient poly-Si solar cell device. (C) 2013 Elsevier B.V. All rights reserved.