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Publications (10 of 646) Show all publications
Dai, H., Yang, L. & He, S. (2019). < 50-mu m thin crystalline silicon heterojunction solar cells with dopant-free carrier-selective contacts. Nano Energy, 64, Article ID UNSP 103930.
Open this publication in new window or tab >>< 50-mu m thin crystalline silicon heterojunction solar cells with dopant-free carrier-selective contacts
2019 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 64, article id UNSP 103930Article in journal (Refereed) Published
Abstract [en]

Dopant-free carrier-selective contacts are emerging in the field of crystalline silicon (c-Si) photovoltaic solar cells, which are potential to further improve the power conversion efficiency (PCE) and lower the cost of c-Si solar cells. Here, we demonstrate tens of microns thin c-Si heterojunction solar cells with substochiometric MoOx and LiFx as dopant-free hole- and electron-selective contacts, respectively. Chemical thinning of 200-mu m thick c-Si wafers enables the production of proof of concept devices with good flexibility and strong performance. When the wafer thickness is reduced to 49.4 mu m (24.7% of the initial thickness), the power conversion efficiency (PCE) of the solar cell still maintains 88.2% of the initial value for the 200-mu m thick cell. When the wafer thickness becomes less than 10% (or even 3.4%) of the initial value, 61.2% and 39.2% of the initial PCEs are still achieved for the 14.8- and 6.8-mu m thick cells, respectively. Passivating and carrier-selective effects of the MoOx and LiFx films allow for the maintenance of performance. An oxide interlayer at the MoOx/c-Si interface passivates the dangling bonds of the c-Si surface and improves the minority carrier lifetime. Field-effect passivation and carrier-selective effects induced by the band bending near the MoOx/c-Si interface and the Al/LiFx/c-Si interface play an important role in maintaining high open-circuit voltage and high fill factor. To the best of our knowledge, this is the first time that <100-mu m thin c-Si heterojunction solar cells are reported with undoped contacts. Our solar cells have been fabricated on thin c-Si wafers with low-temperature processes and without additional doping, and thus our work provides a promising cost-effective means in the field of thin and flexible c-Si solar cells.

Place, publisher, year, edition, pages
ELSEVIER, 2019
Keywords
Crystalline silicon heterojunction solar cell, Dopant-free carrier-selective contacts, Thin wafer, Passivation, Band bending
National Category
Physical Sciences
Research subject
Physics, Material and Nano Physics
Identifiers
urn:nbn:se:kth:diva-262783 (URN)10.1016/j.nanoen.2019.103930 (DOI)000487931500042 ()2-s2.0-85069922344 (Scopus ID)
Note

QC 20191022

Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-11-26Bibliographically approved
Chen, M., Xue, S., Liu, L., Li, Z., Wang, H., Tan, C., . . . He, S. (2019). A highly stable optical humidity sensors based on nano-composite film. Sensors and actuators. B, Chemical, 287, 329-337
Open this publication in new window or tab >>A highly stable optical humidity sensors based on nano-composite film
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2019 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 287, p. 329-337Article in journal (Refereed) Published
Abstract [en]

We report a highly stable humidity sensor based on nanocomposite film obtained by depositing Au nanoparticles on the surface of 3-mercaptopropionic acid (MPA) capped CdTe quantum dots (QDs) and then modifying NaOH (CdTe@Au/NaOH). The CdTe@Au/NaOH film will form compound salts that can be dissolved or crystallized with humidity changes, resulting in a significant absorption variation of green light, which is very benefit for water vapor detection. In this study, we systematically investigated the influence on the performance of humidity sensing by varying the thickness of Au layer as well as the concentration of NaOH. Our results show that the quickest response-recovery time (˜less than 30 s) was found in the sensing film with the Au layer thickness of 20 nm and NaOH concentration of 1M, which can be ascribed to the combined effects of the better morphology and the yield of compound salts. The repeatable response and recovery measurements demonstrate that the designed sensors exhibit an ultralow humidity detection level with fast response-recovery time, high stability and reproducibility at room temperature. The simplicity, low fabrication cost, and wide working range of the humidity sensor will pave the way for its application in environments and gas detection.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Nano-composite film, Optical humidity sensors, Quantum dots, Transmission
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-246419 (URN)10.1016/j.snb.2019.02.051 (DOI)000461341700041 ()2-s2.0-85061797327 (Scopus ID)
Note

QC 20190401

Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-04-03Bibliographically approved
Sun, F., Guo, S., Li, B., Liu, Y. & He, S. (2019). An Acoustic Metamaterial Lens for Acoustic Point-to-Point Communication in Air. Paper presented at IMENTE A, 2012, J APPL PHYS LETT, V100, Xu, 2014, SCIENTIFIC REPORTS, V4, ynolds D. D., 1981, Engineering Principles of Acoustics: Noise and Vibration Control, brovnitskii Yu. I., 2014, ACOUSTICAL PHYSICS, V60, P371 jumdar A., 2005, Journal of Optical and Fiber Communications Reports, V2, P345 ang Xue, 2014, APPLIED PHYSICS LETTERS, V104, ilbin T G, 2010, Geometry and Light: The Science of Invisibility, u Jie, 2013, SCIENTIFIC REPORTS, V3, nchis L., 2013, PHYSICAL REVIEW LETTERS, V110, o Fen, 2013, JOURNAL OF APPLIED PHYSICS, V113, Tinghua, 2012, ACOUSTICAL PHYSICS, V58, P642 Qiannan, 2012, APPLIED PHYSICS LETTERS, V101, en Huanyang, 2007, APPLIED PHYSICS LETTERS, V91, mmer Steven A., 2007, NEW JOURNAL OF PHYSICS, V9, nano Juan C., 2006, OPTICS EXPRESS, V14, P9627 Borui, 2018, APPLIED PHYSICS EXPRESS, V11, Borui, 2017, APPLIED PHYSICS EXPRESS, V10, n Fei, 2017, JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, V142, P1213 Guancong, 2016, SCIENCE ADVANCES, V2, mmer Steven A., 2016, NATURE REVIEWS MATERIALS, V1, ure Cedric, 2016, APPLIED PHYSICS LETTERS, V108, brovnitskii Yu. I., 2015, ACOUSTICAL PHYSICS, V61, P255 i Jun, 2012, NATURE COMMUNICATIONS, V3, ang Zixian, 2012, PHYSICAL REVIEW LETTERS, V108,. Acoustical Physics, 65(1), 1-6
Open this publication in new window or tab >>An Acoustic Metamaterial Lens for Acoustic Point-to-Point Communication in Air
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2019 (English)In: Acoustical Physics, ISSN 1063-7710, E-ISSN 1562-6865, Vol. 65, no 1, p. 1-6Article in journal (Refereed) Published
Abstract [en]

Acoustic metamaterials have become a novel and effective way to control sound waves and design acoustic devices. In this study, we design a 3D acoustic metamaterial lens (AML) to achieve point-to-point acoustic communication in air: any acoustic source (a speaker) in air enclosed by such an AML can produce an acoustic image where the acoustic wave is focused (the field intensity is at a maximum, and the listener can receive the information), while the acoustic field at other spatial positions is low enough that listeners can hear almost nothing. Unlike a conventional elliptical reflective mirror, the acoustic source can be moved around inside our proposed AML. Numerical simulations are given to verify the performance of the proposed AML.

Place, publisher, year, edition, pages
PLEIADES PUBLISHING INC, 2019
Keywords
acoustic metamaterials, focusing, Eaton lens
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-252419 (URN)10.1134/S1063771019010111 (DOI)000467043300001 ()2-s2.0-85065415437 (Scopus ID)
Conference
IMENTE A, 2012, J APPL PHYS LETT, V100, Xu, 2014, SCIENTIFIC REPORTS, V4, ynolds D. D., 1981, Engineering Principles of Acoustics: Noise and Vibration Control, brovnitskii Yu. I., 2014, ACOUSTICAL PHYSICS, V60, P371 jumdar A., 2005, Journal of Optical and Fiber Communications Reports, V2, P345 ang Xue, 2014, APPLIED PHYSICS LETTERS, V104, ilbin T G, 2010, Geometry and Light: The Science of Invisibility, u Jie, 2013, SCIENTIFIC REPORTS, V3, nchis L., 2013, PHYSICAL REVIEW LETTERS, V110, o Fen, 2013, JOURNAL OF APPLIED PHYSICS, V113, Tinghua, 2012, ACOUSTICAL PHYSICS, V58, P642 Qiannan, 2012, APPLIED PHYSICS LETTERS, V101, en Huanyang, 2007, APPLIED PHYSICS LETTERS, V91, mmer Steven A., 2007, NEW JOURNAL OF PHYSICS, V9, nano Juan C., 2006, OPTICS EXPRESS, V14, P9627 Borui, 2018, APPLIED PHYSICS EXPRESS, V11, Borui, 2017, APPLIED PHYSICS EXPRESS, V10, n Fei, 2017, JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, V142, P1213 Guancong, 2016, SCIENCE ADVANCES, V2, mmer Steven A., 2016, NATURE REVIEWS MATERIALS, V1, ure Cedric, 2016, APPLIED PHYSICS LETTERS, V108, brovnitskii Yu. I., 2015, ACOUSTICAL PHYSICS, V61, P255 i Jun, 2012, NATURE COMMUNICATIONS, V3, ang Zixian, 2012, PHYSICAL REVIEW LETTERS, V108,
Note

QC 20190716

Available from: 2019-07-16 Created: 2019-07-16 Last updated: 2019-07-16Bibliographically approved
Xu, B., Zhao, K., Ying, Z., Sjoberg, D., He, W. & He, S. (2019). Analysis of Impacts of Expected RF EMF Exposure Restrictions on Peak EIRP of 5G User Equipment at 28 GHz and 39 GHz Bands. IEEE Access, 7, 20996-21005
Open this publication in new window or tab >>Analysis of Impacts of Expected RF EMF Exposure Restrictions on Peak EIRP of 5G User Equipment at 28 GHz and 39 GHz Bands
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2019 (English)In: IEEE Access, E-ISSN 2169-3536, Vol. 7, p. 20996-21005Article in journal (Refereed) Published
Abstract [en]

Above 6 GHz, radio frequency (RF) electromagnetic field (EMF) exposure from the mobile communication user equipment (UE) should be assessed in terms of incident power density, rather than specific absorption rate as below 6 GHz. Such regulatory RF EMF restrictions will constrain the transmit power of the UE and its peak equivalent isotropically radiated power (EIRP). This paper provides an analysis of the peak EIRP levels of UE containing code-book-based beamforming arrays at 28 GHz and 39 GHz. Different types of antenna elements, incremental element spacing, 4- and 8-element array configurations, and realistic housing integration are considered. The analysis and results show that in realistic housing integration, the 3GPP requirements on minimum peak EIRP can be generally met under the expected RF EMF exposure restrictions.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2019
Keywords
5G, antenna array, EIRP, RF EMF exposure, incident power density, millimeter wave, user equipment
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-247854 (URN)10.1109/ACCESS.2019.2897271 (DOI)000460554100001 ()2-s2.0-85062913955 (Scopus ID)
Note

QC 20190326

Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2019-05-16Bibliographically approved
Xia, J., Tang, J., Bao, F., Evans, J. & He, S. (2019). Channel competition in emitter-plasmon coupling. Optics Express, 27(21), 30893-30908
Open this publication in new window or tab >>Channel competition in emitter-plasmon coupling
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2019 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 21, p. 30893-30908Article in journal (Refereed) Published
Abstract [en]

When an emitter is close to a plasmonic nanoantenna, besides coupling to the dipolar antenna mode, the emitter also considerably couples to a superposition of the high-order modes, referred to as a pseudomode. We comprehensively investigate the differences between the dipolar mode channel and the pseudomode channel in a representative system where a dipole emitter couples to a silver nanorod. The two channels are shown to be distinct in their mechanisms, characteristics (including chromatic dispersion and field distribution), and dependences on system parameters (including emitter-antenna distance, antenna geometry, and material loss). The study provides physical insight and reveals important design rules for controlling the competition between the two channels.

Place, publisher, year, edition, pages
OPTICAL SOC AMER, 2019
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-263344 (URN)10.1364/OE.27.030893 (DOI)000489954500125 ()2-s2.0-85073614226 (Scopus ID)
Note

QC 20191119

Available from: 2019-11-19 Created: 2019-11-19 Last updated: 2019-11-19Bibliographically approved
Li, J., Liu, H., Zhang, S., Zhang, Y. & He, S. (2019). Compact broadband circularly-polarised antenna with a backed cavity for UHF RFID applications. IET Microwaves, Antennas & Propagation, 13(6), 789-795
Open this publication in new window or tab >>Compact broadband circularly-polarised antenna with a backed cavity for UHF RFID applications
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2019 (English)In: IET Microwaves, Antennas & Propagation, ISSN 1751-8725, E-ISSN 1751-8733, Vol. 13, no 6, p. 789-795Article in journal (Refereed) Published
Abstract [en]

A compact broadband circularly-polarised (CP) antenna is designed with a novel method for universal ultra-high-frequency (UHF) radio-frequency identification (RFID) readers. It is composed of a compact ring-shaped patch which aims to decrease the size of the antenna. A quadrature 3 dB coupler placed below the ground plane creates 90 degrees phase differences to generate the CP radiation of the antenna. To improve the performance of the proposed antenna and minimise its size, the authors use a coupling feeding method, an FR4 dielectric slab, and a metal cavity. The coupled feeding is implemented to eliminate the mismatching between the long probe and the ring-shaped patch, and to improve the gain over the operating band. The introduction of an FR4 dielectric slab and a cavity can reduce the antenna size and improve the impedance matching and axial-ratio (AR) bandwidth. The antenna with a backed cavity can increase the front-to-back ratio remarkably and improve the CP performance further. The measured results show that the antenna with a low profile (0.45 lambda(0) x 0.45 lambda(0) x 0.06 lambda(0) at 915 MHz) has the impedance bandwidth of 30.2% (730-990 MHz) and 3 dB AR bandwidth of 24.2% (760-970 MHz). Both the impedance and the AR bandwidth cover the worldwide UHF RFID band.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-252971 (URN)10.1049/iet-map.2018.5321 (DOI)000468055500013 ()2-s2.0-85065993526 (Scopus ID)
Note

QC 20190812

Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-08-12Bibliographically approved
Wang, N., Evans, J. S., Li, C., Pergamenshchik, V. M., Smalyukh, I. I. & He, S. (2019). Controlled Multistep Self-Assembling of Colloidal Droplets at a Nematic Liquid Crystal-Air Interface. Physical Review Letters, 123(8), Article ID 087801.
Open this publication in new window or tab >>Controlled Multistep Self-Assembling of Colloidal Droplets at a Nematic Liquid Crystal-Air Interface
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2019 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 8, article id 087801Article in journal (Refereed) Published
Abstract [en]

We present a controlled cascade of self-assemblings of colloidal droplets at a nematic liquid crystal-air interface into large-scale ordered structures. Changing the tilt of the droplet-induced elastic dipoles via its dependence on the nematic film thickness, we are able to control the dipole-dipole interaction and thus the self-assembling regime. For a progressively large tilt, droplets form anisotropic lattices, which then transform into arrays of repulsive chains, then to bands of half-period-shifted densely bound chains. These structures with chain order at the inner scale aggregate into different large-scale clusters that have a pronounced circular pattern and are stabilized by the many-body elastocapillary attraction.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-259448 (URN)10.1103/PhysRevLett.123.087801 (DOI)000482215500010 ()31491225 (PubMedID)2-s2.0-85071896889 (Scopus ID)
Note

QC 20190923

Available from: 2019-09-23 Created: 2019-09-23 Last updated: 2019-09-23Bibliographically approved
Liu, Y., Guo, S. & He, S. (2019). Illusion Optics: Disguising with Ordinary Dielectric Materials. Advanced Materials, 31(6), Article ID 1805106.
Open this publication in new window or tab >>Illusion Optics: Disguising with Ordinary Dielectric Materials
2019 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 31, no 6, article id 1805106Article in journal (Refereed) Published
Abstract [en]

Illusion devices are usually designed using transformation optics. Here, a new method is proposed to achieve optical illusions without external devices by elaborately manipulating the scattering potential of an object. In contrast to the conventional transformation optics method, which completely replaces one object by the image of another object using complementary\restoring media and a superlens, the method described here is more of a cosmetic operation for an object, which modifies the scattering pattern of the object to mimic another object by exchanging their scattering potentials in two symmetrical areas in the wave vector domain. Only positive isotropic nonmagnetic materials are introduced in the present method, which is impossible using the conventional method because superlenses require negative-index materials. Both numerical simulations and experimental demonstrations are used to verify the performance of the illusion devices of this method.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2019
Keywords
illusion optics, isotropic dielectric materials, scattering potential, wave vector domains
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-246266 (URN)10.1002/adma.201805106 (DOI)000459630600009 ()30548888 (PubMedID)2-s2.0-85058405420 (Scopus ID)
Note

QC 20190326

Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2019-05-13Bibliographically approved
Fei, C., Hong, X., Zhang, G., Ji, D., Wang, Y. & He, S. (2019). Improving the Performance of Long Reach UOWC With Multiband DFT-Spread. IEEE Photonics Technology Letters, 31(16), 1315-1318
Open this publication in new window or tab >>Improving the Performance of Long Reach UOWC With Multiband DFT-Spread
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2019 (English)In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 31, no 16, p. 1315-1318Article in journal (Refereed) Published
Abstract [en]

In this letter, a multiband discrete-Fourier-transform spread (DFT-spread) is introduced to reduce the peak-to-average-power ratio (PAPR) of discrete multitone (DMT)-based underwater optical wireless communication (UOWC) system. The performance of different multiband DFT-spread DMT schemes in a wide underwater transmission range (from 5 to 55 m at a fixed transmission data rate of 5.6 Gb/s) is experimentally investigated. The measured results show that the 1-band DFT-spread and 2-band DFT-spread DMT can significantly improve the system performance compared with the conventional clipping DMT, while the 1-band DFT-spread gives the best performance. Due to the single carrier frequency domain equalization-like characteristic, the 1-band DFT-spread exhibits a relatively uniform signal-to-noise ratio (SNR) profile, which shows the robustness to high frequency fading in the band-limited UOWC system. These intrinsic advantages could jointly ease the bit error rate (BER) deterioration in a long reach UOWC system. Furthermore, the measured data rate-distance product has reached 308 Gb/s*m (i.e., 55-m * 5.6 Gb/s), which to the best of our knowledge is the largest for the single modulation format.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2019
Keywords
Underwater optical wireless communication (UOWC), multiband DFT-spread, discrete multi-tone (DMT), visible laser diode (LD)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-255725 (URN)10.1109/LPT.2019.2923527 (DOI)000476811600002 ()2-s2.0-85069793626 (Scopus ID)
Note

QC 20190814

Available from: 2019-08-14 Created: 2019-08-14 Last updated: 2019-08-14Bibliographically approved
Yang, L., Xu, X., Yuan, Y., Li, Z. & He, S. (2019). Meter-scale transparent conductive circuits based on silver nanowire networks for rigid and flexible transparent light-emitting diode screens. Optical Materials Express, 9(12), 4483-4496
Open this publication in new window or tab >>Meter-scale transparent conductive circuits based on silver nanowire networks for rigid and flexible transparent light-emitting diode screens
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2019 (English)In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 9, no 12, p. 4483-4496Article in journal (Refereed) Published
Abstract [en]

Meter-scale transparent conductive circuits based on silver nanowire (AgNW) networks are fabricated for transparent light-emitting diode (LED) screens on both rigid and flexible substrates. A 25-cm long AgNW transparent conductive strip is fabricated with a strip resistivity of 9.95 Omega/cm. A high uniformity is achieved in terms of film optical transmission (up to 84.5% in average) and sheet resistance (as low as 4.7 Omega/sq in average), superior to ITO. A transparent LED screen based on a 1.2-m ultralong AgNW circuit is demonstrated with LEDs emitting bright red, green and blue lights under different biases. The AgNW strip on a polyethylene terephthalate substrate shows mechanical flexibility and stable performance in bending tests. Based on this, a flexible transparent LED screen is proposed and presented. It works well when dynamically bent to a radius as small as similar to 15 mm. Therefore, the AgNW transparent conductive circuits are very promising as a replacement to ITO circuits for such smart screens, to be integrated into modern glass architectures and display videos in various public places.

Place, publisher, year, edition, pages
Optical Society of America, 2019
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-265484 (URN)10.1364/OME.9.004483 (DOI)000499348700001 ()
Note

QC 20191213

Available from: 2019-12-13 Created: 2019-12-13 Last updated: 2019-12-13Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3401-1125

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