Calcium contacts to n-type crystalline silicon solar cells

Date

2017

Authors

Allen, Thomas
Bullock, James
Zheng, Pei
Vaughan, Ben
Barr, Matthew
Wan, Yimao
Samundsett, Christian
Walter, Daniel
Javey, Ali
Cuevas, Andres

Journal Title

Journal ISSN

Volume Title

Publisher

John Wiley & Sons Inc

Abstract

Direct metallization of lightly doped n-type crystalline silicon (c-Si) is known to routinely produce non-Ohmic (rectifying) contact behaviour. This has inhibited the development of n-type c-Si solar cells with partial rear contacts, an increasingly popular cell design for high performance p-type c-Si solar cells. In this contribution we demonstrate that low resistance Ohmic contact to n-type c-Si wafers can be achieved by incorporating a thin layer of the low work function metal calcium (ϕ ~2.9 eV) between the silicon surface and an overlying aluminium capping layer. Using this approach, contact resistivities of ρc ~2mΩcm2 can be realised on undiffused n-type silicon, thus enabling partial rear contacts cell designs on n-type silicon without the need for a phosphorus diffusion. Integrating the Ca/Al stack into a partial rear contact solar cell architecture fabricated on a lightly doped (ND = 4.5 × 1014 cm-3 ) n-type wafer resulted in a device efficiency of η = 17.6% where the Ca/Al contact comprised only ~1.26% of the rear surface. We demonstrate an improvement in this cell structure to an efficiency of η = 20.3% by simply increasing the wafer doping by an order of magnitude to ND = 5.4 × 1015 cm-3

Description

Keywords

partial rear contacts, dopant-free contacts, calcium, work function, barrier height, contact resistance

Citation

Source

Progress in Photovoltaics: Research and Applications

Type

Journal article

Book Title

Entity type

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Restricted until

2099-12-31