Conference Paper

n-Type silicon - Enabling efficiencies > 20% in industrial production

DOI: 10.1109/PVSC.2010.5614203 Conference: Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE
Source: IEEE Xplore

ABSTRACT

In the first part of this paper we estimate the efficiency potential of crystalline silicon solar cells on conventionally pulled p-type boron-doped Czochralski-grown silicon with typical oxygen concentrations. Taking into account an industrial high-efficiency cell structure featuring fine-line metallization, shallow and well-passivated emitter and a rear surface structure with dielectric passivation and local laser-fired point contacts, the maximum achievable efficiency is around 20%. The main limitation of such a cell is due to the rather low bulk lifetime after light-induced degradation. Even when avoiding the metastable boron-oxygen defect by using Gallium-doped or magnetic Cz-silicon, it has to be kept in mind that the detrimental impact of metal contaminations on p-type silicon is greater than on n-type silicon. A potential strategy to reduce this loss is the use of n-type silicon. Therefore, the second part of the paper discusses different architectures for solar cells on n-type silicon substrates and shows the latest results achieved at Fraunhofer ISE in this field.

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Available from: Stefan W. Glunz
    • "Almost 30% of the final cost of a module corresponds to the growth, cutting and preparation of the silicon wafer (SEMI-PVGroup, 2013), and even though a reduction of more than 10% has taken place since 2010, there is still room to improve. The current commercial cells have a thickness of around 200 lm mainly due to mechanical stability reasons ; however, it has been shown that the high diffusion lengths now available, and the optimizations in passivation and light trapping technologies, allow for an optimal thickness of around 130 lm, in which it is possible to achieve maximum efficiencies (Glunz et al., 2010). Due to the success of recent developments in multi-wire saw slicing with diamond fixed-abrasives, wafer thickness of 150 lm or even less are now industrially feasible (Watanabe et al., 2010;Yu et al., 2012), allowing significant savings in material. "
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    • "The PERT type cells fabricated at UNSW have conversion efficiencies of 21.9% and 21.1% on FZ and CZ n-type substrates, respectively. Fraunhofer ISE was also involved in fabricating a high efficiency solar cell on n-type substrates by adopting the passivated emitter rear locally diffused (PERL) structure and reported efficiencies of 23.4% [46] and 23.9% [35] with Al2O3 passivation at the emitters of the cells. "
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