Profilometry of thin films on rough substrates by Raman spectroscopy

Ledinský, Martin; Paviet‐Salomon, Bertrand; Vetushka, Aliaksei; Geissbühler, Jonas; Tomasi, A.; Despeisse, M.; Wolf, Stefaan De; Ballif, Christophe; Fejfar, A.

doi:10.1038/srep37859

Cited by 14 publications

(9 citation statements)

References 27 publications

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“…When analyzing thin films, this remaining signal from the substrate is a distraction at best and the source of significant error at worst (e.g., if the thin film is μc‐Si:H), and thus RCD is not helpful in determining the minimum tolerable film thickness for Raman analysis. (Note that Ledinský et al recently demonstrated a particular case in which signal from the substrate can be advantageous: They calculated the thickness of a‐Si:H films from the remaining Raman signal from the substrate ).…”

Section: Resultsmentioning

confidence: 99%

Substrate‐independent analysis of microcrystalline silicon thin films using UV Raman spectroscopy

Carpenter

Bailly

Boley³

et al. 2017

Physica Status Solidi (b)

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Surface‐sensitive UV Raman spectroscopy is used to analyze the crystallinity of silicon films less than 20 nm thick directly on silicon wafers. The 325‐nm excitation has a Raman detection thickness of only 13 nm within the silicon film, thus eliminating signal from the substrate. We demonstrate measured crystallinities of microcrystalline silicon thin films that are consistent with the microstructure observed in transmission electron microscopy. Comparison is also made to ellipsometry, which is less able to accurately determine crystallinity than UV Raman spectroscopy. The UV Raman approach is particularly useful for layers grown on substrates of the same material but with different microstructure, and can be extended to non‐silicon materials.

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Section: Resultsmentioning

confidence: 99%

Substrate‐independent analysis of microcrystalline silicon thin films using UV Raman spectroscopy

Carpenter

Bailly

Boley³

et al. 2017

Physica Status Solidi (b)

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“…Second, in the tunnel-IBC design the deposited Si:H(p) layer has a uniform thickness. This eliminates the problem of insufficient charge-collecting film thickness along the perimeter of the contacts 43,44 that is associated with the tapered doped layer profiles produced by in situ shadowmask patterning 45,46 .…”

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confidence: 98%

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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“…While this is very advantageous, the industrial compatibility of using reusable shadow masks is debatable. Moreover, depositions through masks lead to tapered profiles of deposited films and require proximal contact of wafers with the masks …”

Section: Introductionmentioning

confidence: 99%

“…Moreover, depositions through masks lead to tapered profiles of deposited films and require proximal contact of wafers with the masks. 14 Another popular "litho-free" alternative to patterning, which is contact-less and also drastically reduces the number wet chemical steps, is laser ablation-assisted patterning. [15][16][17][18][19][20] In this approach, the pattern is often directly structured onto a sacrificial mask layer on top of the a-Si:H stack to be patterned.…”

Section: Introductionmentioning

confidence: 99%

A novel silicon heterojunction IBC process flow using partial etching of doped a‐Si:H to switch from hole contact to electron contact in situ with efficiencies close to 23%

Radhakrishnan

Uddin

et al. 2019

Progress in Photovoltaics

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We present a novel process sequence to simplify the rear‐side patterning of the silicon heterojunction interdigitated back contact (HJ IBC) cells. In this approach, interdigitated strips of a‐Si:H (i/p+) hole contact and a‐Si:H (i/n+) electron contact are achieved by partially etching a blanket a‐Si:H (i/p+) stack through an SiOx hard mask to remove only the p+ a‐Si:H layer and replace it with an n+ a‐Si:H layer, thereby switching from a hole contact to an electron contact in situ, without having to remove the entire passivation. This eliminates the ex situ wet clean after dry etching and also prevents re‐exposure of the crystalline silicon surface during rear‐side processing. Using a well‐controlled process, high‐quality passivation is maintained throughout the rear‐side process sequence leading to high open‐circuit voltages (VOC). A slightly higher contact resistance at the electron contact leads to a slightly higher fill factor (FF) loss due to series resistance for cells from the partial etch route, but the FF loss due to J02‐type recombination is lower, compared with reference cells. As a result, the best cell from the partial etch route has an efficiency of 22.9% and a VOC of 729 mV, nearly identical to the best reference cell, demonstrating that the developed partial etch process can be successfully implemented to achieve cell performance comparable with reference, but with a simpler, cheaper, and faster process sequence.

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Profilometry of thin films on rough substrates by Raman spectroscopy

Cited by 14 publications

References 27 publications

Substrate‐independent analysis of microcrystalline silicon thin films using UV Raman spectroscopy

Substrate‐independent analysis of microcrystalline silicon thin films using UV Raman spectroscopy

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

A novel silicon heterojunction IBC process flow using partial etching of doped a‐Si:H to switch from hole contact to electron contact in situ with efficiencies close to 23%

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