Growth process conditions of tungsten oxide thin films using hot-wire chemical vapor deposition

Tungsten oxide (WO x ) can be incorporated into amorphous/crystalline silicon heterojunction solar cells as hole contact and for interface modification between p-type amorphous silicon and indium tin oxide. This paper aims at understanding the influence of tungsten oxides properties on silicon heterojunction solar cells. Using in-system photoelectron spectroscopy on thermally evaporated WO x layers, it was verified that WO x with a stoichiometry close to WO 3 features a work function close to 6 eV and is therefore suitable as hole contact on silicon. Additionally the oxygen vacancy concentration in WO x was measured using photoelectron spectroscopy. High oxygen vacancy concentrations in WO x lead to a low band bending in the WO x /silicon-junction. Furthermore solar cells were fabricated using the same WO x , and the band bending in these cells is correlated with their fill factors (FF) and open circuit voltages (V OC ).Combining these results, the following picture arises: Positively charged oxygen vacancies raise the Fermi-level in WO x and reduce the band bending at the WO x /silicon-junction. This, in turn, leads to reduced V OC and FF. Thus, when incorporating WO x into silicon solar cells it is important to minimize the oxygen vacancy density in WO x . Therefore deposition methods, enabling adjustment of the WO x stoichiometry are preferable.

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“…Therefore different methods for it's deposition like reactive sputtering [32] and chemical vapor deposition [33] should be employed.…”

Section: Solar Cell Resultsmentioning

confidence: 99%

Oxygen vacancies in tungsten oxide and their influence on tungsten oxide/silicon heterojunction solar cells

Mews

Korte

Rech

2016

Solar Energy Materials and Solar Cells

148

105

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“…Hereto the samples are loaded onto a sample holder in a 13.5 dm 3 vacuum chamber [18], which is evacuated to 1.0 × 10 −7 mbar. Two parallel straight tungsten filaments (GoodFellow, 10.5 cm in length and 0.3 mm in diameter, 99.95% purity), situated 1 cm directly above the samples, are resistively heated by a constant direct current of 8.0 A, which thus constitutes a filament temperature of 2160 ± 30°C [17]. Then a flow of 100 standard cubic centimeter per minute (sccm) H 2 of 1.0 mbar is introduced.…”

Section: Conditions For Synthesis Route #1: W 24 O 68 /W 24 O 68 Nanomentioning

confidence: 99%

“…Next, an air flow of 25 sccm of a pressure P air = 0.039 mbar is introduced for 30 min, defining the duration of deposition. These conditions result in W 24 O 68 nanostructured crystallite films [17]. After 30 min the air flow is terminated and a H 2 flow of 100 sccm of a pressure of 0.14 mbar is introduced for a period of 1 min.…”

Section: Conditions For Synthesis Route #2: W 24 O 68 /W 24 O 68 Nanomentioning

confidence: 99%

“…This is performed to reduce the surface of the W 24 O 68 crystallites and thus to form centers for nucleation of new tungsten oxide. Next, the H 2 flow is terminated and an air flow of 25 sccm of a pressure P air = 2.0 × 10 −3 mbar is introduced, for a period of 15 min, which is a recipe for the growth of W 24 O 68 nanowires [17].…”

Section: Conditions For Synthesis Route #2: W 24 O 68 /W 24 O 68 Nanomentioning

confidence: 99%

“…Previously we reported the hot-wire chemical vapor deposition (HWCVD) of amorphous WO 3 − x thin films [16] and crystalline nanostructured depositions of a controllable morphology [17] and a W 24 O 68 composition [18]. In those studies only a resistively heated W filament (as source of W atoms), an oxidizing air flow at subatmospheric pressure and a substrate heated to 700 ± 100°C, were used.…”

Section: Introductionmentioning

confidence: 99%

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Hetero- and homogeneous three-dimensional hierarchical tungsten oxide nanostructures by hot-wire chemical vapor deposition

et al. 2015

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Metallic Tungsten Nanostructures and Highly Nanostructured Thin Films by Deposition of Tungsten Oxide and Subsequent Reduction in a Single Hot‐Wire CVD Process

Harks

Houweling

Jong

et al. 2012

Chemical Vapor Deposition

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The synthesis of metallic tungsten nanostructures and highly nanostructured thin films is presented. Crystalline tungsten oxide nanostructures are deposited on glassy carbon substrates kept at 700 AE 100 8C by oxidizing resistively heated tungsten filaments in an air flow under subatmospheric pressures. The internal morphology of the deposited tungsten oxide can be reproducibly controlled by the air pressure. After deposition, the tungsten oxides have been fully reduced to metallic tungsten by atomic hydrogen at a temperature of about 730 8C. Polycrystalline metallic tungsten nanofibers, nanocrystallites, closed crystallite films, and nanogranular films are thus obtained in a single procedure involving deposition and subsequent reduction, at relatively low temperatures.

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Growth process conditions of tungsten oxide thin films using hot-wire chemical vapor deposition

Cited by 24 publications

References 97 publications

Oxygen vacancies in tungsten oxide and their influence on tungsten oxide/silicon heterojunction solar cells

Oxygen vacancies in tungsten oxide and their influence on tungsten oxide/silicon heterojunction solar cells

Hetero- and homogeneous three-dimensional hierarchical tungsten oxide nanostructures by hot-wire chemical vapor deposition

Metallic Tungsten Nanostructures and Highly Nanostructured Thin Films by Deposition of Tungsten Oxide and Subsequent Reduction in a Single Hot‐Wire CVD Process

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