Efficient silicon solar cells with dopant-free asymmetric heterocontacts

• Published in: Nature energy Vol. 1; no. 3; p. 15031
• Main Authors: Bullock, James, Hettick, Mark, Geissbühler, Jonas, Ong, Alison J., Allen, Thomas, Sutter-Fella, Carolin M., Chen, Teresa, Ota, Hiroki, Schaler, Ethan W., De Wolf, Stefaan, Ballif, Christophe, Cuevas, Andrés, Javey, Ali
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 25.01.2016; Nature Publishing Group
• Subjects: 639/301/1005/1007; 639/301/299/946; 639/624/1075/524; Alkali metals; Amorphous silicon; Asymmetry; Dopants; Economics and Management; Energy; Energy conversion efficiency; Energy Policy; Energy Storage; Energy Systems; Fabrication; Fluorides; Free electrons; Insulators; Interlayers; Low temperature; Metal fluorides; Metal oxides; Optoelectronics; Photovoltaic cells; Photovoltaics; Renewable and Green Energy; Silicon; Solar cells
• ISSN: 2058-7546; 2058-7546
• DOI: 10.1038/nenergy.2015.31

A salient characteristic of solar cells is their ability to subject photo-generated electrons and holes to pathways of asymmetrical conductivity—‘assisting’ them towards their respective contacts. All commercially available crystalline silicon (c-Si) solar cells achieve this by making use of doping in either near-surface regions or overlying silicon-based films. Despite being commonplace, this approach is hindered by several optoelectronic losses and technological limitations specific to doped silicon. A progressive approach to circumvent these issues involves the replacement of doped-silicon contacts with alternative materials which can also form ‘carrier-selective’ interfaces on c-Si. Here we successfully develop and implement dopant-free electron and hole carrier-selective heterocontacts using alkali metal fluorides and metal oxides, respectively, in combination with passivating intrinsic amorphous silicon interlayers, resulting in power conversion efficiencies approaching 20%. Furthermore, the simplified architectures inherent to this approach allow cell fabrication in only seven low-temperature (≤200  ∘ C), lithography-free steps. This is a marked improvement on conventional doped-silicon high-efficiency processes, and highlights potential improvements on both sides of the cost-to-performance ratio for c-Si photovoltaics. The use of doped-silicon contacts in silicon solar cells adds cost and complexity to the fabrication process. These issues can now be circumvented by using dopant-free carrier-selective interfaces on silicon, realized by alkali metal fluorides and metal oxides.