Emerging Technologies 2018 Session Listing
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Session E4: Optical Materials and Photovoltaics
Start Time: 09:00, Friday, May 11
Room: Mt. Currie South
Chaired by Guangrui (Maggie) Xia, University of British Columbia (email@example.com)
- 9:00 Magnus Borgström, Lund University
Nanowires for tandem junction solar cells
Semiconducting nanowires are promising materials for high-performance electronics and optics for which optical and electrical properties can be tuned individually. The nanowires are suggested for future high efficiency solar cells due to excellent light absorbing properties. Using nanowires covering only about 12 % of the surface, record efficiencies of VLS grown nanowires has been reported for InP nanowires of 13.8 % and for GaAs nanowires of 15.3%. Recently 17.8 % efficiency was reported for top down fabricated nanowires. In order to further optimize the performance of nanowire photovoltaics, and integrate them on Si in a tandem junction configuration, nanowires with dimensions corresponding to optimal light harvesting capability are necessary. We developed nano imprint lithography for large area patterning of catalytic metal particles with a diameter of 200 nm in a hexagonal pitch of 500 nm. We found that a pre anneal and nucleation step was necessary to keep the particles in place during high temperature annealing to remove surface oxides. We intend to transfer these grown nanowires to a Si platform either by direct growth on Si PV, or by nanowire peel off in polymer, followed by transfer and electrical contacting, or by aerotaxy and alignment for transfer to Si. This work was performed within NanoLund and supported by the Swedish Research Council, the Swedish Foundation for Strategic Research (SSF), the Knut and Alice Wallenberg Foundation and the Swedish Energy Agency. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 641023 (Nano-Tandem) and the European Union’s FP7 programme under grant agreement No 608153 (PhD4Energy). This publication reflects only the author’s views and the funding agency is not responsible for any use that may be made of the information it contains.
- 9:20 Daichi Suzuki, Tokyo Institute of Technology
Multi-view terahertz imaging with nano-carbon flexible scanners
Visualization techniques via terahertz (THz) frequency waves have a great potential for the use in powerful non-invasive inspection methods due to their unique abilities of high penetration and fingerprint spectra of molecules. Most real objects have various three-dimensional curvatures; however, conventional THz imaging technologies are mainly limited to flat samples, hampering accurate measurements of such objects. In this talk, we will present our recent results on a wideband, flexible and portable THz scanner based on an array of carbon nanotube (CNT) THz detectors, which enables multi-view THz imaging without bulky systems. We will focus on three of the topics: 1) Thermal device design for enhancement in scanner performance such as sensitivity, detection speed, and spatial resolution, 2) fabrication of microscale free-standing CNT film arrays, and 3) demonstration of multi-view THz imaging toward the practical use in nondestructive inspections.
- 9:40 François Léonard, Sandia National Laboratories
Inkjet printed terahertz detector
Terahertz waves have shown promise for a number of applications but challenges in developing sources and detectors in this frequency range have prevented broader adoption of the technology. On the detector side, recent work has focused on developing imaging arrays and in improving their performance, which often requires cooling of devices made by photolithography on rigid substrates. Here we present a different approach that focuses on room-temperature detection using inkjet-printed carbon nanotube (CNT) devices. The inkjet printing approach allows for facile, on-the-fly design and printing of devices, including in array format. The structural flexibility of the devices opens new avenues for imaging in non-planar geometries. In this presentation, I will discuss the challenges in developing and printing CNT inks for this particular application, and their properties in the THz. Results of THz detection of CNT pixel arrays will be presented, as well as the factors that impact performance.
- 10:00 Peter Bermel, Purdue University
Toward an integrated system for compact solar thermophotovoltaic generation
Solar thermophotovoltaics (STPV) can convert solar heat into electricity via solar heating, followed by thermal radiation illuminating a photovoltaic diode. STPV can operate with high power densities, no moving parts, and can potentially exceed the standard photovoltaic efficiency limit of ~31%, because of spectral squeezing. However, state-of-the-art STPV demonstrations are still well below theoretical limits, because of losses from collecting solar thermal power, as well as generating and efficiently converting thermal radiation. In response, we present the following experimental demonstrations of key components needed for improved performance: (1) a thin-film Si-based selective solar thermal absorber and emitter, stable up to ~700 degrees C; and (2) a passive radiative cooler to reduce the operating temperature and thus increase the operating voltage of low-bandgap photovoltaic diodes. Finally, we will examine how these components can be integrated into a full STPV demonstration that includes selective solar absorbers, thermal emitters and all-passive, radiatively-enhanced cooling. This work may help pave the way to demonstrating reliable, quiet, light-weight, and sustainable STPV power generation.
- 10:20 COFFEE BREAK
(Mt. Curie Foyer)
- 10:40 Antonio Agresti, Università degli Studi di Roma "Tor Vergata"
with S. Pescetelli, F. Bonaccorso, A. Di Carlo1
Perovskite and 2D materials: a winning paradigm for new generation photovoltaics
In the last decades, the energy demand exponential growth pushed the scientific community in developing novel and innovative technologies devoted in producing energy from clean and renewable sources. Among that, solar energy could potentially provide energy amount 6000 times higher than the energy demand. Nowadays, high-efficient silicon-based photovoltaics dominates the market despite the high production costs and the remarkable energy pay-back time. Alternative thin-film technologies such CIGS or CdTE can represent a cheaper alternative but the toxicity of some constituent materials such as cadmium will represent a serious issue in terms of the panel disposal.
In this context, perovskite solar cells have recently attracted attention due to the surprising power conversion efficiency surpassing 22% on small area devices. Moreover the possibility to tune electrical and optical properties of perovskite crystals combined with low cost solution-based manufacturing processes encouraged the research in scaling-up the perovskite technology from lab-scale cells to large-area modules. However, the possibility to reach high efficiency on large area devices is still limited by the poor control of large scale perovskite film deposition penalizing the active film morphology and eventually its light harvesting and charge collection properties. In particular, the poor morphology and poor stability under real working conditions of the perovskite/charge transport layers interfaces still represent a bottle neck for perovskite devices when compared with the already developed thin-film technology.  In that context, graphene and other 2D materials are here proposed as a powerful tool to improve the morphology control of perovskite layer during the deposition process , to stabilize the resulting interfaces between the stacked device layers  and to improve the charge collection at the electrode by increasing the device efficiency.
Together with the demonstrated stability improvement of GRMs-based perovskite solar cell [6,7] the feasibility of a reproducible scaling-up procedure to realize perovskite solar modules are here proposed as a viable route to make perovskite technology ready to satisfy the efficiency, stability and cost targets required by the photovoltaic market.
ACKNOWLEDGEMENTS This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 696656r - GrapheneCore1.
REFERENCES 1. W. S. Yang, B.-W. Park, E. H. Jun, N. J. Jeon, Y. C. Kim, D. U. Lee, S. S. Shin, J. Seo, E. K. Kim, J. H. Noh, S. Seok, "Iodide management in formamidinium-lead-halide—based perovskite layers for efficient solar cells", Science 356, 1376-1379 (2017). 2. B. Wang, X. Xiao, T. Che "Perovskite Photovoltaics: A High-Efficiency Newcomer to the Solar Cell Family", Nanoscale, 6, 12287-12297 (2014). 3. F. Biccari, F. Gabelloni, E. Burzi, M. Gurioli, S. Pescetelli, A. Agresti, A. E. Del Rio Castillo, A. Ansaldo, E. Kymakis, F. Bonaccorso, A. Di Carlo, A. Vinattieri, Adv. Energy Mater. 1701349 (2017). 4. Y. Busby, A. Agresti, S. Pescetelli, A. Di Carlo, C. Noel, J.-J. Pireaux, L. Houssiau, "Aging Effects in Interface-Engineered Perovskite Solar Cells with 2D Nanomaterials: a Depth Profile Analysis," Materials Today:Energy, just accepted (2018). 5. A. Agresti, S. Pescetelli, A. L. Palma, A. E. Del, R. Castillo, D. Konios, G. Kakavelakis, S. Razza, L. Cinà, E. Kymakis, F. Bonaccorso, and A. Di Carlo, "Graphene Interface Engineering for Perovskite Solar Modules: 12.6% Power Conversion Efficiency over 50 cm2 Active Area", ACS Energy Lett. 2, 279 (2017). 6. Agresti, A.; Pescetelli, S.; Najafi, L.; Castillo, A. E. D. R.; Busby, Y.; Carlo, A. Di. Carlo, "Graphene and Related 2D Materials for High Efficient and Stable Perovskite Solar Cells", IEEE International Conference on nanotechnology; IEEE Xplore (2017). 7. A. Agresti, S. Pescetelli, B. Taheri, A. E. Del Rio Castillo, L. Cinà, F. Bonaccorso, and A. Di Carlo, "Graphene-Perovskite Solar Cells Exceed 18% Efficiency: A Stability Study", ChemSusChem 9, 2609 (2016).
- 11:00 Stefano Gregori, University of Guelph
Energy conversion and harvesting in low-power systems
This talk will introduce a discrete-time circuit analysis technique tailored to the implementation of energy conversion and harvesting in low-power systems.
A new approach based on two-port equivalent models and z-domain analysis will be presented. Such approach easily allows to study the dynamic response and the energy consumption during transient. Both capacitor-based and inductor-based power converters will be considered and the results will be compared to conventional circuit simulations.
Energy harvesters based on force-sensitive mechanically-variable capacitors will be also introduced. A prototype electrostatic harvester for low-power wearable devices will be shown. The device is based on flexible and biodegradable nanocellulose films and is designed to operate without startup battery.
- 11:20 Han Yun, University of British Columbia
with N. Jaeger
Broadband optical power splitters for integrated photonic circuits using Si metamaterial on an SOI platform
Adiabatic 3-dB couplers are 2x2 optical power splitters that are used in photonic integrated circuits for splitting/combining light. In them, light injected into one port of the coupler is split evenly between the two output ports. Due to the high- index-contrast, silicon-on-insulator (SOI) adiabatic 3-dB couplers usually suffer from large footprints. Si metamaterial based structures, e.g., sub-wavelength-grating-based (SWG-based) structures, provide the flexibility to engineer both the refractive index and the dispersion properties of SOI devices and can be used in adiabatic 3-dB couplers to achieve compact sizes.
Here, we summarize our recent work done towards achieving compact broadband 2x2 adiabatic 3-dB couplers using Si metamaterial based waveguides. First, we present work towards a 3-dB coupler having two parallel 20 μm long conventional SWG waveguides for adiabatic mode evolution of transverse electric modes to achieve 3-dB power splitting over an operating bandwidth of 130 nm with a splitting imbalance of <0.3 dB. Then, we present work towards an adiabatic 3-dB coupler using two parallel 15 μm long SWG-assisted strip waveguides having a theoretically predicted operating bandwidth of 500 nm.
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