Magnesium Fluoride Electron-Selective Contacts for Crystalline Silicon Solar Cells

Wan, Yimao; Samundsett, Christian; Bullock, James; Allen, Thomas G.; Hettick, Mark; Yan, Donghang; Zheng, Peiting; Zhang, Xinyu; Cui, Jie; McKeon, Josephine A; Javey, Ali; Cuevas, Andrés

doi:10.1021/acsami.6b03599

Cited by 205 publications

(196 citation statements)

References 54 publications

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“…[39] The existence of TaO x N y and TaO x phases might be mainly attributed to the reaction of the Ta precursor with residual oxygen in the ALD chamber. The ρ c value of the TaN x /Si heterocontact is comparable to that of the electron-selective TiO 2 and MgF 2 contacts, [17,21] which indicates that the TaN x contact can be suitable for the fabrication of high-efficiency c-Si solar cells. Figure 3a shows the dark J-V curves of Al/Si Schottky structures (Figure 3a inset), with and without a 2.5 nm thick TaN x interlayer between the front Al circular contact and the silicon substrate.…”

Section: Resultsmentioning

confidence: 75%

Tantalum Nitride Electron‐Selective Contact for Crystalline Silicon Solar Cells

Yang

Aydın

et al. 2018

Advanced Energy Materials

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133

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Minimizing carrier recombination at contact regions by using carrier‐selective contact materials, instead of heavily doping the silicon, has attracted considerable attention for high‐efficiency, low‐cost crystalline silicon (c‐Si) solar cells. A novel electron‐selective, passivating contact for c‐Si solar cells is presented. Tantalum nitride (TaN x ) thin films deposited by atomic layer deposition are demonstrated to provide excellent electron‐transporting and hole‐blocking properties to the silicon surface, due to their small conduction band offset and large valence band offset. Thin TaNx interlayers provide moderate passivation of the silicon surfaces while simultaneously allowing a low contact resistivity to n‐type silicon. A power conversion efficiency (PCE) of over 20% is demonstrated with c‐Si solar cells featuring a simple full‐area electron‐selective TaNx contact, which significantly improves the fill factor and the open circuit voltage (Voc) and hence provides the higher PCE. The work opens up the possibility of using metal nitrides, instead of metal oxides, as carrier‐selective contacts or electron transport layers for photovoltaic devices.

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Section: Resultsmentioning

confidence: 75%

Tantalum Nitride Electron‐Selective Contact for Crystalline Silicon Solar Cells

Yang

Aydın

et al. 2018

Advanced Energy Materials

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133

142

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“…We underline that our device concept may also be suitable for other materials used in passivating contacts, such as transition metal oxide or alkali earth metal and alkali metal fluoride materials [60][61][62]72 . We recall an earlier work where a TiO x thin film, interposed between p-and n-type a-Si:H films connecting two sub-cells of a tandem thin-film device, was found to be beneficial for the performance of the solar cell 73 .…”

Section: High-e Ciency Proof-of-concept Tunnel-ibc Solar Cellsmentioning

confidence: 99%

Simple processing of back-contacted silicon heterojunction solar cells using selective-area crystalline growth

et al. 2017

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For crystalline-silicon solar cells, voltages close to the theoretical limit are nowadays readily achievable when using passivating contacts. Conversely, maximal current generation requires the integration of the electron and hole contacts at the back of the solar cell to liberate its front from any shadowing loss. Recently, the world-record e ciency for crystalline-silicon singlejunction solar cells was achieved by merging these two approaches in a single device; however, the complexity of fabricating this class of devices raises concerns about their commercial potential. Here we show a contacting method that substantially simplifies the architecture and fabrication of back-contacted silicon solar cells. We exploit the surface-dependent growth of silicon thin films, deposited by plasma processes, to eliminate the patterning of one of the doped carrier-collecting layers. Then, using only one alignment step for electrode definition, we fabricate a proof-of-concept 9-cm 2 tunnel-interdigitated backcontact solar cell with a certified conversion e ciency >22.5%. I n recent decades, the market of photovoltaics has been consistently growing and the yearly installed photovoltaic capacity has increased from 328 MW peak in 2001 to 50 GW peak in 2015. This resulted in 2016 in a cumulative capacity of 235 GW peak (ref. 1), largely based on crystalline-silicon (c-Si) solar-cell technologies 2 , and contributing to about 1.3% of the global electricity production 3 . To further increase this number, the cost-competitiveness of photovoltaics must surpass that of classic, non-renewable energy sources, and one route towards this goal is to raise the conversion efficiency of industrial c-Si solar cells 4,5 .High power conversion efficiencies require maximizing the solar-cell electrical parameters: open-circuit voltage (V oc ), fillfactor (FF) and short-circuit current density (J sc ). For the V oc and FF, this is possible by using passivating contacts, employing silicon oxide or hydrogenated amorphous silicon (a-Si:H) thin films to minimize charge carrier recombination at the electrical contacts to the c-Si wafer, with demonstrated record efficiencies for two-sidecontacted solar cells of 25.1% (refs 6,7). Maximum J sc values can be achieved using a back-contacted architecture, eliminating front metal electrode shadowing and minimizing optical reflection and absorption losses at the front. Small-sized back-contacted solar cells, based on diffused silicon homo-junctions, were realized at several research institutes (refs 8-11), showing a best conversion efficiency up to 24.4% (ref. 12). Industrially, the back-contacted architecture was pioneered by Sunpower, recently reporting on large-area devices with very high J sc values and efficiencies surpassing 25% (ref. 13). Considering these achievements, integrating passivating contacts in a back-contacted architecture is the obvious c-Si single-junction solar-cell design towards highest conversion efficiencies. Such an approach has increasingly been researched in both academia and indust...

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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%

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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Magnesium Fluoride Electron-Selective Contacts for Crystalline Silicon Solar Cells

Cited by 205 publications

References 54 publications

Tantalum Nitride Electron‐Selective Contact for Crystalline Silicon Solar Cells

Tantalum Nitride Electron‐Selective Contact for Crystalline Silicon Solar Cells

Simple processing of back-contacted silicon heterojunction solar cells using selective-area crystalline growth

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

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