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Heterojunctions between zinc oxide nanostructures and organic semiconductor
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lighting is a big business, lighting consumes considerable amount of the electricity. These facts motivate for the search of new illumination technologies that are efficient. Semiconductor light emitting diodes (LEDs) have huge potential to replace the traditional primary incandescent lighting sources. They are two basic types of semiconductor LEDs being explored: inorganic and organic semiconductor light emitting diodes. While electroluminescence from p-n junctions was discovered more than a century ago, it is only from the 1960s that their development has accelerated as indicated by an exponential increase of their efficiency and light output, with a doubling occurring about every 36 months, in a similar way to Moore's law in electronics. These advances are generally attributed to the parallel development of semiconductor technologies, optics and material science. Organic light emitting diodes (OLEDs) have rapidly matured during the last 30 years driven by the possibility to create large area light-emitting diodes and displays. Another driving force to specifically use semiconducting polymers is the possibility to build the OLED on conventional flexible substrates via low-cost manufacturing techniques such as printing techniques, which open the way for large area productions.

This thesis deals with the demonstration and investigation of heterojunction LEDs based on p-organic semiconductor and n-ZnO nanostructures. The ZnOorganic heterojunctions are fabricated using low cost and simple solution process without the need for sophisticated vacuum equipments. Both ZnO-nanostructures and the organic materials were grown on variety of substrates (i.e. silicon, glass and plastic substrates) using low temperature methods. The growth mechanism of the ZnO nanostructures has been systematically investigated with major focus in ZnO nanorods/nanowires. Different organic semiconductor materials and device configurations are explored starting with single polymer emissive layer ending up with separate emissive and blocking layers, or even blends. Interestingly, the photoluminescence and electroluminescence spectra of the hybrid LEDs provided a broad emission band covering entirely the visible spectrum [∼400-∼800nm]. The hybrid light emitting diode has a white emission attributed to ZnO intrinsic defects and impurities in combination with the electroluminescence from the conjugated polymers. The ZnO nanostructures in contact with a high workfunction electrode constitute an air stable electron injecting contact for the organic semiconductor. Hence, we have shown that a white light emission can be achieved in a ZnO-organic hybrid light emitting diode using cheap and low temperature growth techniques for both organic and inorganic materials.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 51 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1405
Keyword [en]
ZnO nanostructures, Organic semiconductors, LEDs
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-71843ISBN: 978-91-7393-046-8 (print)OAI: oai:DiVA.org:liu-71843DiVA: diva2:454442
Public defence
2011-11-04, TP2, Täppan, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Note
The series number "1504" is incorrect and is changed in the electronic version to the correct number "1405".Available from: 2011-11-07 Created: 2011-11-07 Last updated: 2013-09-12Bibliographically approved
List of papers
1. The demonstration of hybrid n-ZnO nanorod/p-polymer heterojunction light emitting diodes on glass substrates
Open this publication in new window or tab >>The demonstration of hybrid n-ZnO nanorod/p-polymer heterojunction light emitting diodes on glass substrates
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2009 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 95, no 3, 807-812 p.Article in journal (Refereed) Published
Abstract [en]

We report a demonstration of heterojunction light emitting diode (LED) based on a hybrid n-ZnO-nanorod/p-polymer layered structure. The ZnO was grown using the aqueous chemical growth (ACG) on top of the polymer(s) which were deposited on glass. The current-voltage (I-V) behavior of the heterojunctions showed good rectifying diode characteristics. Room-temperature electroluminescence (EL) spectra of the LEDs provided a broad emission band over a wide LED color range (430-650 nm), in which both zinc and oxygen vacancy peaks are clearly detected. We present here luminescent devices based on the use of ZnO-nanorods in combination with two different blended and multi-layered p-type polymers. Electroluminescence of the first batch of devices showed that white bluish strong emission for the presently used polymers is clearly observed. We obtained a turn-on voltage of 3 V and break-down voltage equal to -6 V for PVK-TFB blended device. The corresponding values for the NPD-PFO multilayer device were 4 V and -14 V, respectively. The rectification factors were equal to 3 and 10 for the two devices, respectively. The films and devices processed were characterized by scanning electron microscopy (SEM), DEKTAK 3ST Surface Profile, Semiconductor Parameter Analyzer, photoluminescence (PL), and electroluminescence (EL).

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17910 (URN)10.1007/s00339-009-5075-8 (DOI)
Available from: 2009-04-26 Created: 2009-04-24 Last updated: 2014-01-15Bibliographically approved
2. The effect of the interlayer design on the electroluminescence and electrical properties of n-ZnO nanorod/p-type blended polymer hybrid light emitting diodes
Open this publication in new window or tab >>The effect of the interlayer design on the electroluminescence and electrical properties of n-ZnO nanorod/p-type blended polymer hybrid light emitting diodes
2009 (English)In: Nanotechnology, ISSN 0957-4484, Vol. 20, no 6, 065710- p.Article in journal (Refereed) Published
Abstract [en]

Hybrid light emitting diodes (LEDs) based on n-ZnO nanorods and blended polymers were fabricated and characterized. The blended polymers consisted of a blue emitting polymer and a charge transport polymer. The effect of the interlayer design on the electrical and electroluminescent characteristics of these hybrid LEDs was investigated. We demonstrated that by adding a calcium (2) acetylacetonate [Ca(acac)(2)] layer between the blended polymer layer and the ZnO nanorods, an increase in device performance was observed. The purpose of the extra layer was to act as a band offset stepping layer (offset divider). Moreover, the effect of the stepper layer thickness for this offset stepping layer was studied. The results indicate that LED performance is greatly affected by the presence and thickness of this band offset stepping layer.

Keyword
ZnO-nanorods, p-type polymer, LEDs
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-16614 (URN)10.1088/0957-4484/20/6/065710 (DOI)
Note
Original Publication: Amal Wadesa, Omer Nour and Magnus Willander, The effect of the interlayer design on the electroluminescence and electrical properties of n-ZnO nanorod/p-type blended polymer hybrid light emitting diodes, 2009, NANOTECHNOLOGY, (20), 6, 065710. http://dx.doi.org/10.1088/0957-4484/20/6/065710 Copyright: Institute of Physics http://www.iop.org/ Available from: 2009-02-11 Created: 2009-02-06 Last updated: 2014-01-15Bibliographically approved
3. Solution processed ZnO nanowires/polyfluorene heterojunctions for large area lightening
Open this publication in new window or tab >>Solution processed ZnO nanowires/polyfluorene heterojunctions for large area lightening
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2010 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 490, no 4-6, 200-204 p.Article in journal (Refereed) Published
Abstract [en]

Hybrid inorganic-organic semiconductor heterojunctions are nowadays scrutinized for optoelectronic devices, such as solar cells and light emitting diodes. Here, ZnO nanowires/polyfluorene heterojunctions have been entirely fabricated from solution by wet chemistry and low temperature processes. The transparent plastic electrode PEDOT injects holes in the polyfluorene, while the electrons are injected via the ZnO-Au contact, thus avoiding the use of air sensitive low work function metals. The hybrid inorganic-organic light emitting diode emits almost white light. Because of its solution processability, stable cathode, low cost and low temperature process, the ZnO/polymer heterojunction devices are promising for large area lightening applications.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-55530 (URN)10.1016/j.cplett.2010.03.050 (DOI)000276822100018 ()
Available from: 2010-04-30 Created: 2010-04-30 Last updated: 2017-02-03Bibliographically approved
4. ZnO-Polymer hybrid electron only rectifiers
Open this publication in new window or tab >>ZnO-Polymer hybrid electron only rectifiers
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The combination of organic semiconductors and ZnO nanorods provides new hybrid devices for large area optoelectronics targeting solar energy harvesting and light emission applications. The electronic transport across organic-ZnO heterojunction is not well understood. Here, we investigate systematically the creation of the ZnOpolymer interface and pinpoint potential issues in hybrid devices based on chemically grown ZnO nanorods. For the sake of simplicity, we focus on a ZnO-polymer hybrid device transporting only electrons. The semiconducting polymer used is poly {[N,N0-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,50-(2,20-dithiophene)}. The device shows easy electron injection from Au/ZnO contacts and a good rectification partially governed by the morphology of the heterojunction.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-71841 (URN) (ISBN)
Projects
Available from: 2011-11-07 Created: 2011-11-07 Last updated: 2017-02-03Bibliographically approved

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