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


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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    ABSTRACT: An in-line and low cost doping procedure has been optimized, suitable of implementation on thin wafers and based on organic and aqueous diluted precursors instead of the traditional POCl3 process, which results in a safer and environmentally friendly process. The influence of the liquid precursor solution in the effective lifetime and the phosphorous depth profile has been studied, along with the potential introduction of trace contaminants.
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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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    ABSTRACT: The p-type crystalline silicon wafers have occupied most of the solar cell market today. However, modules made with n-type crystalline silicon wafers are actually the most efficient modules up to date. This is because the material properties offered by n-type crystalline silicon substrates are suitable for higher efficiencies. Properties such as the absence of boron-oxygen related defects and a greater tolerance to key metal impurities by n-type crystalline silicon substrates are major factors that underline the efficiency of n-type crystalline silicon wafer modules. The bi-facial design of n-type cells with good rear-side electronic and optical properties on an industrial scale can be shaped as well. Furthermore, the development in the industrialization of solar cell designs based on n-type crystalline silicon substrates also highlights its boost in the contributions to the photovoltaic industry. In this paper, a review of various solar cell structures that can be realized on n-type crystalline silicon substrates will be given. Moreover, the current standing of solar cell technology based on n-type substrates and its contribution in photovoltaic industry will also be discussed.
    Full-text · Article · Dec 2013 · The Scientific World Journal
    • "In recent years, aluminium oxide (Al 2 O 3 ) received a vast amount of attention in the silicon photovoltaic (PV) community as Al 2 O 3 provides an excellent level of surface passivation on most c-Si surfaces, particularly on p-type c-Si surfaces including p + emitters [1 – 5]. This excellent surface passivation can be maintained at the solar cell device level as was demonstrated by a solar cell efficiency of 23.9% for an n-type passivated emitter rear locally diffused (PERL) solar cell featuring a p + emitter passivated by Al 2 O 3 [6] [7]. "
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    ABSTRACT: The origin behind crystalline silicon surface passivation by Al2O3 films is studied in detail by means of spatially-resolved electron energy loss spectroscopy. The bonding configurations of Al and O are studied in as-deposited and annealed Al2O3 films grown on c-Si substrates by plasma-assisted and thermal atomic layer deposition. The results confirm the presence of an interfacial SiO2-like film and demonstrate changes in the ratio between tetrahedrally and octahedrally coordinated Al in the films after annealing. These observations reveal the underlying origin of c-Si surface passivation by Al2O3. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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