Overview of Nano-Tandem's results

The project has made advances in both monolithic nanowire integration route and in transfer route. It has been demonstrated that GaAs nanowire solar cells are suitable for space application as their radiation hardness is much higher than that of planar cells. Further, it has been showed that InGaP nanowire p-n junctions can be directly grown on Si for tandem solar cells. For InP nanowires grown on native substrate, the conversion efficiency was improved beyond the state-of-the-art. Tunnel diodes inside nanowires have been demonstrated. Low-cost aerotaxy method has shown its ability to synthesise p-n junction nanowires and ternary allow nanowires. Rear-side photonic light trapping suitable for a direct integration of nanowires on Si solar cell has been developed, which led to a new world record in conversion efficiency of III-V on Si solar cells (33.3% published in Nature Energy). The environmental impact of the nanowire PV technology was assessed on the lab scale and on the industrial scale and suggestions for limiting the negative ecological impact have been formulated.

In the following, we detail the key project results by category 

Mastering of template-assisted selective epitaxy growth of GaAsP and InGaP nanowires

Nano-Tandem project has produced major advances in mastering of TASE growth of different III-V materials. The growth of ternary alloys with a bandgap corresponding to the optimal value for III-V on Si tandem solar cells was developed.
GaAsP and InGaP nanowires were vertically grown on Si inside oxide templates defined by lithography. The key parameters controlling the optimal alloy composition namely the growth temperatures and the V/III flux ratio were determined. Nanowires of a homogeneous composition have been achieved. These experiments demonstrate that InGaP with the proper composition can be integrated directly on Si using TASE
Bologna et al., ACS Appl. Mat. Int, 2018, 10.1021/acsami.8b10770

Doping investigation and demonstration of axial p-n junctions in TASE nanowires

The next step towards a monolithically integrated III-V nanowire cell on Si is the doping control. Doping calibration in InGaP nanowires was performed in a feed-back loop with structural and electrical characterizations. Structural analyses evidenced an impact of the doping incorporation on the alloy composition, which should be compensated to achieve homogeneous ternary nanowires. The major result of this investigation is the demonstration of active p-n junctions in InGaP nanowires grown on Si. Single nanowire current-voltage characteristics were combined with electron beam induced current microscopy to extract the junction parameters. Figure 1 illustrates the activity of the p-n junction probed on a single nanowire level. One important result of this investigation is the demonstration of a low-loss collection of the generated carriers through the Si substrate. In parallel, the optimization of the TASE growth and doping of GaAs nanowires on Si was also performed.
Piazza et al., APL 2019, 10.1063/1.5085405
Bologna et al., ACS Appl. Mat. Int, 2018, 10.1021/acsami.8b10770 
Nanowire containing p-n junction, schematic and SEM image with EBIC
Figure 1 : Schematic of a nanowire containing an InGaP p-n junction; SEM image of a single nanowire superimposed with the corresponding EBIC signal of the junction. (The scale bars correspond to 200 nm.)

The impact of the Nano-Tandem progress in template assisted growth of III-V semiconductors on Si goes well beyond the photovoltaic community. It also covers other applications such a III-V on silicon photonics, electronics, etc.


Development of ternary alloy nanowires with 1.7 eV bandgap

The main building block of the top cell is the array of ternary nanowires with a well-controlled morphology, composition and doping. First, the nanowire growth preserving the pattern defined by nanoimprint lithography was developed. The influence of doping on the composition of ternary nanowires was understood and controlled. The InGaP nanowires with a bandgap close to 1.7 eV and a good nanowire-to-nanowire and intra-nanowire compositional homogeneity were achieved.
Otnes et al, Nano Research 2016, 10.1007/s12274-016-1165-z
Otnes et al, Nano Lett. 2017, 10.1021/acs.nanolett.6b03795


Optimization of the InP nanowire solar cell efficiency

Nano-Tandem project has pushed forward the conversion efficiency of binary InP nanowire solar cells. For InP nanowire grown by a bottom-up approach the new record has been set at 15%. This progress has been achieved thanks to a feedback loop between the growth, high through-put nanoscale analyses and optimization of the fabrication technology. By correlating the single nanowire measurements to performance of fully processed nanowire array solar cells, we identified how the performance limiting parameters are related to growth and/or processing conditions. The results are highlighted in Figure 2. Doping profile and post-growth surface passivation were optimized based on electron beam induced current microscopy: extended generation profiles in individual nanowires were achieved. This understanding was used to achieve a more than sevenfold improvement in efficiency of InP nanowire solar cells. The best cell showed a certified efficiency of 15.0%, the highest reported value for a bottom-up synthesized InP nanowire solar cell.
Otnes et al., Nano Lett. 2018, 10.1021/acs.nanolett.8b00494.
 
Single nanowire EBIC and current-voltage measurements
Figure 2 : Progress of InP nanowire solar cells. Left : Single nanowire EBIC and current-voltage measurements. Right : achieved current-voltage curves under solar illumination showing the improvement of the cell.

Demonstration of tunnel diodes in nanowires

For tandem architecture, the subcell electrical connection requires a tunnel diode. Realisation of this diode in nanowires is a big challenge since degenerate doping with an abrupt profile is difficult to obtain in catalyst-assisted growth. In the Nano-Tandem project this roadblock was removed. InP/GaInP nanowire tunnel diodes were demonstrated for the first time. A maximum peak current density of 25 A/cm2, and maximum peak to valley current ratio of 2.5 at room temperature were achieved. The realization of nanowire tunnel diodes in both InP/GaInP and GaInP/InP configurations opens new opportunities for nanowire tandem solar cells independent of the growth order of the different materials.
Zeng et al., Nano Research, 2018, 10.1007/s12274-017-1877-8

Demonstration of nanowire peel-off and substrate reuse

In order to make nanowire solar cells economically viable, one requirement within the Nano-Tandem project is to crate technology for recycling of the substrate. The optimization of the nanowire peel-off and substrate cleaning allowed to repeat the nanowire growth three times on the same substrate without any apparent degradation of the nanowire morphology.
Borgstrom et al, IEEE J Photovolt. 2018, 10.1109/JPHOTOV.2018.2816264

Demonstration of functional solar cells from peeled off nanowire membranes

In Nano-Tandem project, we have demonstrated small size nanowire membrane solar cells with conversion efficiency of 3.5%. This demonstration is based on GaAs nanowire arrays grown on 2′′ GaAs wafers, which were embedded into a polymer layer and peeled off their growth substrate. To enable mechanical peel-off, only a thin passivation layer could be used, which reduced the short-circuit current density of the membrane cells (Jsc = 6.8 mA/cm2) in comparison to the best substrate-integrated cells. The open-circuit voltage was nearly identical to the open-circuit voltage of cells integrated into wafer, while the fill factor was significantly lower, a result of series resistance at least in part due to the not yet optimized rear contact. This represents the first demonstration of fully functional substrate-independent nanowire cells.
Borgstrom et al, IEEE J Photovolt. 2018, 10.1109/JPHOTOV.2018.2816264

Evaluation of the potential of nanowire solar cells for space applications

In addition, we have evaluated the potential of nanowire solar cells for space applications. Space power systems require solar cells with a high specific power (i.e., power to weight ratio) and the main technology employed nowadays is multijunction solar cells based on III-V semiconductor materials. However, harsh space environment oblige the use of thick cover glass to shield the solar cells from high energy particles present in space, which ultimately limits the specific power of multijunction space solar cells.
We have irradiated nanowire solar cells with high energy protons and electrons and performed numerical simulations to interpret our results. As a benchmark, planar III-V solar cells were also employed in our study. Our findings indicate that nanowire solar cells degradation after irradiation is significantly lower than their planar III-V counterparts. Consequently, the high radiation tolerance of nanowire solar cells, explained by the array geometry and nanometric dimensions, reduces the need for shielding. Thus nanowire solar cells hold promise for a new, efficient, lightweight, radiation-tolerant power-generating system for space applications.
Espinet-Gonzales et al, IEEE J Photovolt. 2020, 10.1109/JPHOTOV.2020.2966979
Espinet-Gonzales et al, ACS Nano 2019, 10.1021/acsnano.9b05213

Demonstration of aerotaxy-grown GaAsP nanowires with 1.7 eV bandgap

Synthesis of ternary alloy nanowires by Aerotaxy was demonstrated for the first time within Nano-Tandem project Bandgap-tunable GaAsP nanowires with various P content (going from 0 to 43%) were demonstrated and their structural and optical properties were assessed. Bandgaps between 1.61 eV and 2.06 eV were achieved covering the range interesting for dual-junction GaAsP/Si solar cells. It was shown that regardless of the composition and the growth temperature, nanowires have a pure zincblende crystal structure. The carrier lifetime was characterized by time-resolved photoluminescence.
Metaferia et al., Nano Lett., 2016, 10.1021/acs.nanolett.6b02367


Demonstration of GaAs nanowire pn-junctions grown by low-cost high throughput Aerotaxy

To grow nanowires containing a p-n junction for the Nano-Tandem project, a dedicated reactor with multiple chambers was designed and fabricated. The growth of n-doped nanowires was optimized using an addition of tetramethyltin into the chamber. Carrier concentrations in the 1019 cm-3 range has been achieved. The growth procedure for p-n junction nanowires is shown in Figure 3. To introduce p-doping, catalyst particles are annealed in presence of trimethylgallium and diethylzinc (DEZn), which leads to enrichment of the seed particles with Ga and Zn. These elements are then incorporated into the nanowires, Zn results in a p-type doping. The combination of the p- and n-doped segments grown in consecutive growth chambers resulted in nanowire pn-junctions having excellent diode characteristics with a rectification ratio of >105, an ideality factor around 2, and very promising photoresponse. The electrical properties and diffusion lengths were shown to be comparable to nanowires grown using metal organic vapor phase epitaxy. These findings demonstrate that high-quality GaAs nanowire pn-junctions can be produced using a low-cost technique suitable for mass-production, paving the way for industrial-scale production of nanowire-based solar cells
Metaferia et al., Nanotechn. 2018 10.1088/1361-6528/aabec0
Barrigoń, Nano Lett. 2018, 10.1021/acs.nanolett.7b04609
 

Schematic of the Aerotaxy process
Figure 3 : Schematic of the Aerotaxy growth process of p-n junction nanowires (Barrigón et al, Nano Lett. 2018, 18, 1088-1092)

High throughput characterization method using electron beam induced current microscopy

One important challenge for nanowire solar cell optimization is the measurement and control of the nanowire nanoscale electrical properties. The electrical parameters of nanoscale junctions can be assessed using a combination of optical methods (photoluminescence or cathodoluminescence) and electron beam induced current (EBIC) microscopy. The approach, developed within Nano-Tandem project, allows a process-free characterization thanks to the use of nano-manipulators integrated into an SEM chamber which can be used to address individual nanowires in an array with a high measurement throughput. Hence, the samples can be investigated “as-grown”, lowering significantly the time needed for the characterization and eliminating any artefact arising from the fabrication steps. Thanks to the nanoscale analyses, InP nanowire cell conversion efficiency has been improved to a new record of 15% (see Figure 2). This method has also enabled the optimization of template assisted nanowire p-n junctions (see Figure 1).
Piazza et al., Nanoscale 2018, 10.1039/c8nr03827a
Otnes et al., Nano Lett. 2018, 10.1021/acs.nanolett.8b00494
Piazza et al., APL 2019, 10.1063/1.5085405

Boosting Si solar cell response with photonic light trapping

High-efficiency Si solar cells commonly use light-trapping features, such as random pyramids on the front side, to compensate for the weak near-bandgap absorption. However, structuring the front side is not compatible with the direct integration of nanowire solar cell on top.  In Nano-Tandem project, we have developed an optically structured back side beneath the p+ passivating contact shown in Figure 4. It features a diffractive crossed grating made of a polymeric resist, covered with silver that is evaporated on top. The diffractive structure is defined by the nanoimprint lithography technique, which can be applied on large areas. The implemented grating goes beyond the state of the art in various respects. The grating consists of a low-refractive-index epoxy material. Due to the etching step for the removal of the resist residual layer, the epoxy surface features a stochastic nanostructure that introduces additional scattering. The silver layer itself is modulated and therefore plays a strong active role in the light trapping. Finally, this photonic light-trapping structure acts at the same time as the electrical contact, thus forming a metallic photonic contact layer. This technological development of Nano-Tandem project has an impact not only for nanowire/Si solar cells, but also for a wide range of other augmented Si cells.
Cariou et al., Nat. En. 2018, 10.1038/s41560-018-0125-0
 
 
Backside photonic light trapping
Figure 4 : Back-side photonic light-trapping grating. Left: SEM image of the back side of the Si solar cell with a passivated contact and a nanoimprint grating covered by evaporated silver. Right : A photograph of the 4-inch solar cell back side with nanoimprinted grating diffracting the incident light.

New world record efficiency of III-V/Si tandem solar cells

By using the photonic light trapping on the rear side of the Si cell developed within Nano-Tandem, a new record efficiency was established for III–V/Si solar cells. The device was fabricated using wafer bonding to permanently join a GaInP/GaAs top cell with a silicon bottom cell. The key issues of III–V/Si interface recombination and silicon's weak absorption were addressed using poly-silicon/SiOx passivating contacts and a novel rear-side diffraction grating for the silicon bottom cell. With these combined features, we demonstrate a two-terminal GaInP/GaAs//Si solar cell reaching a 1-sun AM1.5G conversion efficiency of 33.3%. Thanks to this development, III–V/Si cells reach similar performances to standard III–V/Ge triple-junction solar cells, which a major break-through for high efficiency photovoltaics.
Cariou et al., Nat. En. 2018, 10.1038/s41560-018-0125-0

Life cycle assessment of nanowire-based solar cells

Nanowire-based solar cells have the potential to offer a solar technology with high conversion efficiency by the efficient use of nanomaterials. However, the use of nanomaterials has a potential environmental and human health impact. We showed that the use of nanomaterials might result in high carbon emissions due to the increased energy requirements for the synthesis of nanomaterials. In order to prevent future environmental repercussions of the nanowire-based solar cells developed in Nano-Tandem project, we used life cycle assessment (LCA) to guide the sustainable development of the new technology. LCA is a tool that is used to assess the environmental impact of technologies, by taking into account the whole life cycle of the product; the extraction of raw materials, the manufacturing, operation and end-of-life treatment of the technology, as well as the energy consumption throughout all these stages.
Pallas, G et al., Sustainability 2018, 10.3390/SU10030689

Evaluation of the environmental performance of two different manufacturing routes for the production of nanowire-based solar cells

LCA was carried out at the lab scale, for various impact categories: climate change, land use, eutrophication, acidification, photochemical oxidation, ozone depletion, terrestrial/ marine/ freshwater ecotoxicity and human toxicity. Two manufacturing routes explored in Nano-Tandem were analysed, namely:
•    Direct nanowire integration on Si (Concept I) : GaAs nanowires grown directly on a silicon substrate using template-assisted epitaxy.
•    Transfer route (Concept II) : GaAs nanowires grown on a native substrate, they are peeled-off and transferred to a silicon substrate.
The results are shown in Figure 5. By applying LCA at the early stage of R&D, we have identified dominating environmental hotspots. These hotspots include the use of gold and trifluoromethane (CHF3), as well as the additional impact from the use of a III-V substrate in the transfer route. By applying different scenarios, we identified ways to reduce various impacts.
Pallas, et al., J. Ind. Ecol. 2019, 10.1111/jiec.12855
 

Peer-reviewed publications:

2020

  • "Nanowire Solar Cells: A New Radiation Hard PV Technology for Space Applications." Espinet-Gonzalez, P., E. Barrigon, Y. Chen, G. Otnes, G. Vescovi, C. Mann, J. V. Lloyd, D. Walker, M. D. Kelzenberg, I. Aberg, M. Borgstrom, L. Samuelson and H. A. Atwater (2020).  Ieee Journal of Photovoltaics 10(2): 502-507.
    DOI: 10.1109/JPHOTOV.2020.2966979.
  • "Life cycle assessment of emerging technologies at the lab scale: The case of nanowire-based solar cells." Pallas, Georgios; Vijver, Martina G.; Peijnenburg, Willie J. G. M.; et al. (2020).  JOURNAL OF INDUSTRIAL ECOLOGY, Vol. ‏ , 24 Issue: ‏ 1
    https://doi.org/10.1111/jiec.12855

2019

  • "Synthesis and Applications of III-V Nanowires." Barrigon, E., M. Heurlin, Z. X. Bi, B. Monemar and L. Samuelson (2019). Chemical Reviews 119(15): 9170-9220.
    https://doi.org/10.1021/acs.chemrev.9b00075
  • "Nanoprobe-Enabled Electron Beam Induced Current Measurements on III-V Nanowire-Based Solar Cells." Barrigon, E., G. Otnes, Y. Chen, Y. W. Zhang, L. Hrachowina, X. L. Zeng, L. Samuelson, M. Borgstrom and Ieee (2019). 2019 Ieee 46th Photovoltaic Specialists Conference: 2730-2733.
    DOI: 10.1109/PVSC40753.2019.8980491
  • "Semi-Transparent Perovskite Solar Cells with ITO Directly Sputtered on Spiro-OMeTAD for Tandem Applications." Bett, A. J., K. M. Winkler, M. Bivour, L. Cojocaru, O. S. Kabakli, P. S. C. Schulze, G. Siefer, L. Tutsch, M. Hermle, S. W. Glunz and J. C. Goldschmidt (2019).  Acs Applied Materials & Interfaces 11(49): 45796-45804.
    https://doi.org/10.1021/acsami.9b17241
  • "Three-Dimensional Imaging of Beam-Induced Biasing of InP/GaInP Tunnel Diodes." Cordoba, C., X. L. Zeng, D. Wolf, A. Lubk, E. Barrigon, M. T. Borgstrom and K. L. Kavanagh (2019). Nano Letters 19(6): 3490-3497.
    https://doi.org/10.1021/acs.nanolett.9b00249
  • "Modal analysis of resonant and non-resonant optical response in semiconductor nanowire arrays." Dagyte, V. and N. Anttu (2019).  Nanotechnology 30(2).
    https://doi.org/10.1088/1361-6528/aaea26
  • "Radiation Tolerant Nanowire Array Solar Cells." Espinet-Gonzalez, P., E. Barrigon, G. Otnes, G. Vescovi, C. Mann, R. M. France, A. J. Welch, M. S. Hunt, D. Walker, M. D. Kelzenberg, I. Aberg, M. T. Borgstrom, L. Samuelson and H. A. Atwater (2019).  Acs Nano 13(11): 12860-12869.
    https://doi.org/10.1021/acsnano.9b05213
  • "High Responsivity of InP/InAsP Nanowire Array Broadband Photodetectors Enhanced by Optical Gating."  Karimi, M., X. L. Zeng, B. Witzigmann, L. Samuelson, M. T. Borgstrom and H. Pettersson (2019). "Nano Letters 19(12): 8424-8430.
    https://doi.org/10.1021/acs.nanolett.9b02494
  • "Investigation of GaN nanowires containing AlN/GaN multiple quantum discs by EBIC and CL techniques." Piazza, V., A. V. Babichev, L. Mancini, M. Morassi, P. Quach, F. Bayle, L. Largeau, F. H. Julien, P. Rale, S. Collin, J. C. Harmand, N. Gogneau and M. Tchernychea (2019).  Nanotechnology 30(21).
    DOI: https://doi.org/10.1088/1361-6528/ab055e
  • "Nanoscale analysis of electrical junctions in InGaP nanowires grown by template-assisted selective epitaxy." Piazza, V., S. Wirths, N. Bologna, A. A. Ahmed, F. Bayle, H. Schmid, F. Julien and M. Tchernycheva (2019). Applied Physics Letters 114(10).
    https://doi.org/10.1063/1.5085405

 

2018

  • "Modal analysis of resonant and non-resonant optical response in semiconductor nanowire arrays." Dagyte, V. and N. Anttu (2019). Nanotechnology 30(2). 
    DOI: 10.1088/1361-6528/aaea26
  •  "Dopant-Induced Modifications of GaxIn(1-x)P Nanowire-Based p-n Junctions Monolithically Integrated on Si(111)." Bologna, N., S. Wirths, L. Francaviglia, M. Campanini, H. Schmid, V. Theofylaktopoulos, K. E. Moselund, A. F. I. Morral, R. Erni, H. Riel and M. D. Rossell (2018). Acs Applied Materials & Interfaces 10(38): 32588-32596.
    DOI: 10.1021/acsami.8b10770
  • "Growth kinetics of GaxIn(1-x)P nanowires using triethylgallium as Ga precursor." Dagyte, V., M. Heurlin, X. L. Zeng and M. T. Borgstrom (2018). Nanotechnology 29(39).
    DOI: 10.1088/1361-6528/aad1d2
  • "n-type doping and morphology of GaAs nanowires in Aerotaxy." Metaferia, W., S. Sivakumar, A. R. Persson, I. Geijselaers, L. R. Wallenberg, K. Deppert, L. Samuelson and M. H. Magnusson (2018). Nanotechnology 29(28).
    DOI: 10.1088/1361-6528/aabec0
  • "Electron Tomography Reveals the Droplet Covered Surface Structure of Nanowires Grown by Aerotaxy." Persson, A. R., W. Metaferia, S. Sivakumar, L. Samuelson, M. H. Magnusson and R. Wallenberg (2018). Small 14(33).
    DOI: 10.1002/smll.201801285
  • "Nanoscale investigation of a radial p-n junction in self-catalyzed GaAs nanowires grown on Si (111)." Piazza, V., M. Vettori, A. A. Ahmed, P. Lavenus, F. Bayle, N. Chauvin, F. H. Julien, P. Regreny, G. Patriarche, A. Fave, M. Gendry and M. Tchernycheva (2018). Nanoscale 10(43): 20207-20217.
    DOI: 10.1039/c8nr03827a
  • Towards Nanowire Tandem Junction Solar Cells on Silicon. Magnus T. Borgstrom, Martin H. Magnusson, Frank Dimroth, Gerald Siefer, Oliver Hohn, Heike Riel, Heinz Schmid, Stephan Wirths, Mikael Bjork, Ingvar Aberg, Willie Peijnenburg, Martina Vijver, Maria Tchernycheva, Valerio Piazza, Lars Samuelson
    IEEE Journal of Photovoltaics 8 (3) May 2018.
    DOI: 10.1109/JPHOTOV.2018.2816264
  • III–V-on-silicon solar cells reaching 33% photoconversion efficiency in two-terminal configuration. Cariou, R., J. Benick, F. Feldmann, O. Höhn, H. Hauser, P. Beutel, N. Razek, M. Wimplinger, B. Bläsi, D. Lackner, M. Hermle, G. Siefer, S. W. Glunz, A. W. Bett and F. Dimroth. Nature Energy (2018)
    DOI:10.1038/s41560-018-0125-0
  • Green and Clean: Reviewing the Justification of Claims for Nanomaterials from a Sustainability Point of View. Pallas G, Peijnenburg WJGM, Guinée JB, Heijungs R, Vijver MG. Sustainability. 2018; 10(3):689.
    https://doi.org/10.3390/su10030689
  • Room-Temperature Lasing from Monolithically Integrated GaAs Microdisks on Silicon. Wirths, S.; Mayer, B.F.; Schmid, H.; Sousa, M.; Gooth, J.; Riel, H.; Moselund, K.E. ACS Nano, Article ASAP.
    DOI: 10.1021/acsnano.7b07911
  • GaAs Nanowire pn-Junctions Produced by Low-Cost and High-Throughput Aerotaxy. Barrigón E, Hultin O, Lindgren D, Yadegari F, Magnusson MH, Samuelson L, Johansson LIM, Björk MT. Nano Lett. 2018 Feb 14;18(2):1088-1092.
    DOI: 10.1021/acs.nanolett.7b04609
  • Intersubband Quantum Disc-in-Nanowire Photodetectors with Normal-Incidence Response in the Long-Wavelength Infrared. Karimi, Mohammad; Heurlin, Magnus; Limpert, Steven; et al. NANO LETTERS 18 (1) 365-372,  JAN 2018
    DOI: 10.1021/acs.nanolett.7b04217
  • Electrical and optical evaluation of n-type doping in InxGa(1-x)P nanowires. X. Zeng*, R. T. Mourão*, G. Otnes*, O. Hultin, V. Dagyte, M. Heurlin, and M.T. Borgström, Nanotechnology 2018,
    DOI: 10.1088/1361-6528/aabaa5.
  • Understanding InP Nanowire Array Solar Cell Performance by Nanoprobe-Enabled Single Nanowire Measurements. Gaute Otnes, Enrique Barrigón, Christian Sundvall, K. Erik Svensson, Magnus Heurlin, Gerald Siefer, Lars Samuelson, Ingvar Åberg, Magnus T. Borgström. Nano Lett., 2018, 18 (5), pp 3038–3046.
    DOI: 10.1021/acs.nanolett.8b00494

2017

2016

 

 

Public documents and reports:

2017

Report on realization of integrated light trapping structures into bottom cell (PDF, 630 KB, New window)

Report on optimized particle patterning with redesigned master structures or processing (PDF, 284 KB, New window)

Report on the electrical design of tandem cell (PDF, 312 KB, New window)

Publishable summary of the preliminary life cycle assessment (PDF, 195 KB, New window)

 

2016

  • Report on adaption of EQE and IV measurement equipment for nanowire solar cells.
    Summary: In this deliverable the work related to the preparation of the set-ups intended for the measurements of the EQE and the light IV curves of the nanowire-Silicon tandem cells to be developed within the project is described. In the case of the EQE measurements this has been mainly related to an adaption of the used bias light illumination via identification and purchase of suitable optical filters. For the light IV measurement work concentrated on the spectrum of the multi-source sun simulator. It turned out that for some potential nanowire-Silicon tandem cells particular blue rich spectra are required. This however could successfully be realized with the simulator at Fraunhofer ISE. In summary it can be stated that the set-ups are now well prepared for the measurement of more or less any potential nanowire-Silicon tandem cell.
    Download report on adaption of EQE and IV measurement equipment for nanowire solar cells (PDF, 300 KB, New window)
  • Report on the status of the different NIL based techniques.
    Summary: In this deliverable, the work related to the patterning of metal nano-particles as catalyst arrays for the highly defined nanowire growth on III/V substrates is described.
    As patterning technique we are evaluating different nanoimprint lithography (NIL) toolings and processes as well as one alternative technique, namely micro-contact
    printing (μCP). As metallisation technique both physical vapour deposition and electroplating are tested. The quality of the realised catalyst arrays is evaluated first
    using scanning electron microscopy (SEM) and atomic force microscopy (AFM). After the following step of epitaxy (work package 2: III/V nanowire growth), the
    quality of the catalyst arrays is rated with respect to optical properties PL energy and luminescence intensity.
    We reproducibly imprint 2” wafers with Au metal particles in a matrix of 200 nm diameter holes and a hexagonal pitch of 500 nm, optimised for light absorption in InP
    NW arrays. NIL is a working method for large scale economically viable patterning.
    Download report on the status of the different NIL based techniques (PDF, 1.1 MB, New window)

SEM of vertical nanowires and EBIC measuring tip

FEATURED

Former Nano-Tandem member Gaute Otnes wins Fulbrights article prize for young researchers 2020. The winning article:

Understanding InP Nanowire Array Solar Cell Performance by Nanoprobe-Enabled Single Nanowire Measurements.

Nano Lett. 2018, 18, 5, 3038–3046

Read the research article at the publisher's site

Prize decision by the Norwegian Fulbright Alumni Association