Epitaxy of Emitters on P-and N-Type Substrates for Crystalline Silicon Solar Cells

Schmich, E.; Reber, S.; Hees, Jakob; Lautenschlager, H.; Schillinger, N.; Willeke, G.

doi:10.1109/wcpec.2006.279355

Cited by 7 publications

(3 citation statements)

References 2 publications

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“…19 Furthermore, these solar cells showed a contact problem, resulting in a bad fill factor. 20 Taking into account that phosphorus outdiffusion occurs during sample cooling, two different methods of preventing this were investigated on cSiTF. The samples were either cooled down under a PH 3 /H 2 atmosphere as described in the previous section or chemically etched after the deposition, in order to remove the surface layer.…”

Section: Cell Resultsmentioning

confidence: 99%

n‐Type emitter epitaxy for crystalline silicon thin‐film solar cells

Schmich

Lautenschlager

Frieß

et al. 2007

Progress in Photovoltaics

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Crystalline silicon thin-film (cSiTF) solar cells are an attractive alternative to bulk silicon solar cells. At Fraunhofer ISE we follow the concept of the epitaxial wafer equivalent (EpiWE), where 20 mm of silicon are deposited epitaxially by high temperature atmospheric pressure CVD (APCVD) on a cheap silicon substrate. The EpiWE can then be processed using standard industrial cell production. Furthermore, it is possible to simplify the solar cell process when depositing the emitter by epitaxy in-situ after the growth of the base. The epitaxial emitter could be an alternative method of n-type emitter processing with adjustable emitter profile and short deposition time. This paper presents results of cSiTF solar cells with epitaxial emitters and photolithographic contacts, which prove the good performance of the emitter and the applicability of the EpiWE to conventional solar cell processes. Included in the discussion is a description of the CVD deposition principle developed at Fraunhofer ISE and the applied clean room solar cell process. The emitter doping profiles and concentrations, as well as the structural quality, are discussed in detail using SIMS and SEM data. The phosphorus out-diffusion during cooling is prevented by cooling the samples in a PH 3 /H 2 atmosphere. Moreover, a double-layer emitter is formed having blue sensitive properties. The internal quantum efficiencies (IQEs) show that the emitter can be passivated as well as a 'standard' emitter formed by POCl 3 diffusion. Efficiencies up to 14Á9 and 13Á6% for large area cSiTF solar cells on highly doped Cz and mc, respectively, are presented.

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Section: Cell Resultsmentioning

confidence: 99%

n‐Type emitter epitaxy for crystalline silicon thin‐film solar cells

Schmich

Lautenschlager

Frieß

et al. 2007

Progress in Photovoltaics

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“…The substrate acts as a conductive, mechanical support and provides a crystal template for the epitaxial growth of the active layer in which all the photovoltaic power is generated. While minimizing the amount of high‐quality silicon makes the cell much cheaper compared to bulk crystalline silicon solar cells 4, 5, the energy conversion efficiency still needs to be high enough to advocate the merits of this cell concept. Since the epilayer is optically thin, light trapping is necessary.…”

Section: Introductionmentioning

confidence: 99%

Gettering of transition metals by porous silicon in epitaxial silicon solar cells

Radhakrishnan

Ahn

Hoeymissen

et al. 2012

Physica Status Solidi (a)

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Epitaxial silicon solar cells (“epicells”) are based on an epitaxial active layer (“epilayer”) grown on top of a low‐cost, inactive p+ silicon substrate. A key challenge is to mitigate transition metal out‐diffusion from the low‐purity substrate into the active layer. An embedded porous silicon (PSi) layer can be used to getter metals within the substrate. This was studied theoretically using density functional theory where large binding energies (∼1.9–2.2 eV) for metal segregation to PSi void surface were calculated for Fe and Cu. Incorporating this in a diffusion model yielded large gettering coefficients of ∼104 even at 1000 °C. To verify this experimentally, a test structure consisting of a 2‐µm thick epilayer grown on top of an 8.5 × 8.5 cm2 area of re‐organized PSi etched into the middle of an 8″ Cz, p+ wafer was used. These wafers were surface‐contaminated with metals (Fe, Ni, Cu) to ∼1014–1015 cm−2 and annealed at high temperatures (950–1000 °C) for up to 15 min. This allowed the metals to distribute throughout the wafer and getter to preferential sites. Direct total reflection X‐ray fluorescence mapping of Cu on the front side showed that the embedded PSi reduced the amount of Cu reaching the top surface by ∼103 times, compared to the areas without PSi. Moreover, SIMS depth profiling revealed large metal concentrations (1018–1019 cm−3) in the depth associated with PSi, while the metal concentrations were below detection limits in the surrounding area, suggesting a gettering coefficient of ∼103–104. A slow cooling rate and smaller pore radii were also found to be beneficial for gettering.

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“…Thus, the lower surface dopant concentration will result in poor contact issue that can lead to poor FF of the cells. [35]…”

Section: Materials Characterization Of Epitaxial Emitter Silicon Solamentioning

confidence: 99%

Low temperature silicon-based epitaxy for solar cells applications

Lai¹

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Epitaxy of Emitters on P-and N-Type Substrates for Crystalline Silicon Solar Cells

Cited by 7 publications

References 2 publications

n‐Type emitter epitaxy for crystalline silicon thin‐film solar cells

n‐Type emitter epitaxy for crystalline silicon thin‐film solar cells

Gettering of transition metals by porous silicon in epitaxial silicon solar cells

Low temperature silicon-based epitaxy for solar cells applications

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