Fabrication of ‘finger-geometry’ silicon solar cells by electrochemical anodisation
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Cells made from crystalline silicon dominate the market for photovoltaics, but improvements in cost-effectiveness are still necessary for uptake to increase. In this paper, we investigate the fabrication of a cell structure which has the potential to be compatible with cheap low-purity silicon substrates. In our cell design the charge-collecting p–n junction protrudes into the substrate like fingers, thus significantly reducing the required carrier diffusion length compared to a front planar junction cell. The macroporous structure is created by electrochemical anodisation of an n-type silicon substrate in an HF and H2O2 (aqueous) electrolyte. The pores are loaded with a boron-containing glass which is then annealed to diffuse the dopant into the silicon substrate forming a volume junction. The anodisation conditions have been optimised using intentionally contaminated single-crystal silicon as a model system. We characterise the junction formed by electron beam induced current and current–voltage measurements. The anodisation study is extended to n-type multicrystalline silicon and it is found that the orientation of the grains strongly influences the geometry of the pores formed. The potential for using this cell structure for low-cost photovoltaics is discussed and potential problems are highlighted.
KeywordsPorous Silicon Anodisation Process Pore Density Electron Beam Induce Current Electrochemical Anodisation
We thank Prof. P.R. Wilshaw (University of Oxford) for initiating the project and for many helpful discussions, Radka Chakalova (University of Oxford) for assistance with sample processing and Dr Semih Senkader (REC Wafer) for provision of the n-type mc-Si wafers. JDM is the holder of a Royal Academy of Engineering/EPSRC Research Fellowship, and an EPSRC First Grant (EP/J01768X/1).
- 14.Lehmann V (2002) In: Electrochemistry of silicon: instrumentation, science, materials and applications, chap. 6. Wiley-VCH Verlag GmbH, Weinheim. doi: 10.1002/3527600272