Plasma-enhanced atomic-layer-deposited MoO x emitters for silicon heterojunction solar cells

Ziegler, Johannes; Mews, Mathias; Kaufmann, Kai; Schneider, Thomas; Sprafke, Alexander; Korte, Lars; Wehrspohn, Ralf B.

doi:10.1007/s00339-015-9280-3

Cited by 37 publications

(49 citation statements)

References 14 publications

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“…Maximization of the solar cell open-circuit voltage (V OC ) to record values of 750 mV [1] has been possible by combining two principles of solar cell design [2]: (1) , alkali salts [ 6 , 7 ] and transition metal oxides (TMOs) [ [8][9][10][11][12][13][14][15][16][17][18] ]. TMOs offer themselves as excellent candidates to substitute traditional c-Si dopants given their wide range of work function values (3 -7 eV) and marked p-or n-type semiconductivity [ 19 ].…”

Section: Introductionmentioning

confidence: 99%

Origin of passivation in hole-selective transition metal oxides for crystalline silicon heterojunction solar cells

et al. 2016

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Transition metal oxides (TMOs) have recently attracted interest as an alternative to boron/phosphorous doped layers in crystalline silicon heterojunction solar cells. In this work, the interface between n-type c-Si (n-Si) and three thermally evaporated TMOs (MoO 3 , WO 3 and V 2 O 5 ) was investigated by transmission electron microscopy and secondary ion-mass/x-ray photoelectron spectroscopy. For the oxides studied, chemical passivation of n-Si was attributed to an ultra-thin (1.9 -2.8 nm) SiO x~1.5 interlayer formed by chemical reaction, leaving oxygen-deficient species (MoO, WO 2 and VO 2 ) as byproducts. Field-effect passivation was also inferred from the inversion (hole-rich) layer induced on the n-Si surface, a result of Fermi level alignment between two materials with dissimilar electrochemical potentials (work function delta Δφ ≥1 eV). Therefore, the holeselective and passivating functionality of these TMOs, in addition to their ambient temperature processing, could prove an effective means to lower cost and simplify solar cell processing.

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Section: Introductionmentioning

confidence: 99%

Origin of passivation in hole-selective transition metal oxides for crystalline silicon heterojunction solar cells

et al. 2016

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“…The use of passivating contacts—like the ones used in silicon heterojunction (SHJ) solar cells—suppresses these recombination routes by separating the metal from the surface of the Si wafer and omitting heavy doping of the Si wafer. To reduce further the optical losses in passivating contacts, the application of wide‐bandgap materials like molybdenum‐, tungsten‐, titanium‐, or nickel‐oxide (MoO X ,, WO X , TiO 2 , NiO ), as well as lithium‐ or magnesium‐fluoride (LiF, MgF 2 ) has received much attention in recent years. These materials feature a work function that is either higher than the ionization energy, or lower than the electron affinity of crystalline Si (c‐Si).…”

Section: Introductionmentioning

confidence: 99%

“…Despite its high work function, MoO X is an n‐type material . As a consequence, efficient carrier extraction requires that photogenerated holes in the valence band of c‐Si recombine with electrons present in the MoO X conduction band; the latter electrons are injected from the degenerately n‐type doped TCO . Efficient charge‐carrier transport through this contact stack depends on the thickness, defect density (for trap‐assisted transport) and work function of MoO X , as well as on the line‐up with the band edge energies of the surrounding layers.…”

Section: Introductionmentioning

confidence: 99%

Toward Annealing‐Stable Molybdenum‐Oxide‐Based Hole‐Selective Contacts For Silicon Photovoltaics

et al. 2018

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This is the pre-peer reviewed version of the following article: "Towards annealing-stable molybdenum-oxide-based hole-selective contacts for silicon photovoltaics", which has been published in final form at https://DOI. Sandwiched between a hydrogenated intrinsic amorphous silicon passivation layer and a transparent conductive oxide, this material allows a highly efficient hole-selective front contact stack for crystalline silicon solar cells. However, hole extraction from the Si wafer and transport through this stack degrades upon annealing at 190 °C, which is needed to cure the screen-printed Ag metallization applied to typical Si solar cells. Here, we show that effusion of hydrogen from the adjacent layers is a likely cause for this degradation, highlighting the need for hydrogen-lean passivation layers when using such metal-oxidebased carrier-selective contacts. Pre-MoOX-deposition annealing of the passivating a-Si:H layer is shown to be a straightforward approach to manufacturing MoOX-based devices with high fill factors using screen-printed metallization cured at 190 °C.a Electronic mail: Mathieu.boccard@epfl.ch

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“…• C [8,11] and atomic layer deposition of molybdenum oxide at higher temperature was also found to yield low quality contacts [17,18]. Therefore silicon heterojunction solar cells with molybdenum oxide contacts degrade significantly during curing of common silver pastes [11].…”

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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

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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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Plasma-enhanced atomic-layer-deposited MoO x emitters for silicon heterojunction solar cells

Cited by 37 publications

References 14 publications

Origin of passivation in hole-selective transition metal oxides for crystalline silicon heterojunction solar cells

Origin of passivation in hole-selective transition metal oxides for crystalline silicon heterojunction solar cells

Toward Annealing‐Stable Molybdenum‐Oxide‐Based Hole‐Selective Contacts For Silicon Photovoltaics

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

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