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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    • "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.
    The Scientific World Journal 12/2013; 2013(2):470347. DOI:10.1155/2013/470347 · 1.73 Impact Factor
    • "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)
    physica status solidi (RRL) - Rapid Research Letters 11/2013; 7(11):937-941. DOI:10.1002/pssr.201308081 · 2.14 Impact Factor
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    • "Currently, the industrial crystalline silicon solar cell production is still dominated by p-type silicon solar cells. However, as the silicon PV industry tends to introduce advanced high-efficiency solar cell concepts, the quality of the base material is becoming more and more important [1]. n-type Cz silicon does not suffer from light induced degradation, which is known to occur for p-type Cz silicon due to boron-oxygen pairs [2] [3] [4]. "
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    ABSTRACT: Recently, we presented an industrially feasible passivation and contacting scheme for the front side boron emitter of n-type silicon solar cells based on firing processes. On these cells, efficiencies up to 20.8% have been achieved on small areas. These cells feature a fully-metalized BSF on the rear side, which limits the VOC to about 655mV. When changing to a PERT cell design with a passivated BSF, both the VOC as well as the JSC can be improved due to a reduced recombination at the rear and an improved optical confinement. In this work we studied different POCl3 diffusions for their applicability to n-type PERT solar cells with respect to passivation and metallization. The achieved results have been used to fabricate a first batch of n-type PERT solar cells, on which VOC values up to 671mV have been measured. The improved internal quantum efficiency above 900nm confirms the improvement of the rear side of the cell. The boron emitter of this cell was passivated with a stack of 5Å ALD Al2O3 (four ALD cycles) and 70nm PECVD SiNx. Thus the VOC of 671mV demonstrates furthermore, that the Al2O3 thickness of fired Al2O3/SiNx stacks for the passivation of boron emitters can be drastically reduced to four atomic layers of Al2O3.
    Energy Procedia 12/2011; 8:479-486. DOI:10.1016/j.egypro.2011.06.169
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