Hybrid organic semiconductor/gallium nitride/CMOS smart pixel arrays
Lead Research Organisation:
Imperial College London
Department Name: Physics
Abstract
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Organisations
Publications
Belton C
(2013)
Location, Location, Location - Strategic Positioning of 2,1,3-Benzothiadiazole Units within Trigonal Quaterfluorene-Truxene Star-Shaped Structures
in Advanced Functional Materials
Campoy-Quiles M
(2013)
Advanced Ellipsometric Characterization of Conjugated Polymer Films
in Advanced Functional Materials
Chung D
(2011)
Flexible multilayer inverted polymer light-emitting diodes with a gravure contact printed Cs2CO3 electron injection layer
in Applied Physics Letters
Chung D
(2010)
High performance, flexible polymer light-emitting diodes (PLEDs) with gravure contact printed hole injection and light emitting layers
in Organic Electronics
Huang J
(2009)
Electroluminescence and Laser Emission of Soluble Pure Red Fluorescent Molecular Glasses Based on Dithienylbenzothiadiazole
in Advanced Functional Materials
Kanibolotsky AL
(2011)
Well-defined and monodisperse linear and star-shaped quaterfluorene-DPP molecules: the significance of conjugation and dimensionality.
in Advanced materials (Deerfield Beach, Fla.)
Perevedentsev A
(2014)
Interplay between solid state microstructure and photophysics for poly(9,9-dioctylfluorene) within oriented polyethylene hosts
in Journal of Polymer Science Part B: Polymer Physics
Ryu G
(2009)
Spatial Patterning of the ß -Phase in Poly(9,9-dioctylfluorene): A Metamaterials-Inspired Molecular Conformation Approach to the Fabrication of Polymer Semiconductor Optical Structures
in Advanced Functional Materials
Xia R
(2009)
Low-Threshold Distributed-Feedback Lasers Based on Pyrene-Cored Starburst Molecules with 1,3,6,8-Attached Oligo(9,9-Dialkylfluorene) Arms
in Advanced Functional Materials
| Description | §1. Design, synthesis and characterization of new molecular gain media: (i) Soluble pyrene-cored starbursts, tetra-substituted with bi and ter(9,9-dihexyl?uorene) arms that prevent core p-stacking. Solid-state photoluminescence quantum ef?ciency > 90%, with emission characteristic of isolated-pyrene-centered singlets and near single exponential, ns PL decay. ASE-measured gnet, max = 75 cm-1 with threshold robust against annealing up to 130 °C. Coating 1D etched-silica gratings (240-nm stripe width & 320-nm period) allows construction of distributed feedback lasers with thresholds down to 50 pJ per pulse (10 Hz repetition rate, 4.2 ns duration, 380 nm excitation, 3.2 x 10-4 cm2 area), laser slope ef?ciencies up to 3.9%, and wavelength tuning over 40 nm in the blue/blue-green spectral region. (ii) Soluble red ?uorescent dithienylbenzothiadiazole-based molecular glasses. These materials are effective for red ?uorescent OLEDs, yielding impressive ef?ciencies and have potential as gain media for 650 nm POF applications. (iii) Trigonal quaterfluorene-truxene starbursts with 2,1,3-benzothiadiazole moieties strategically inserted into the otherwise-fluorene-based arms. (iv) Quaterfluorene substituted diketopyrrolopyroles with linear and starbust geometries and their blends with cross-linkable photoresists. (v) Gain media comprising poly(3-hexylthiophene) blended in PFO: Ef?cient Förster energy transfer from F8BT to RR-P3HT yields blend PLQE values of 25% in the red emission range for 20 wt.% RR-P3HT. An optical gain coef?cient g ˜ 50 cm-1 is then observed and the gain spectral maximum can be readily tuned to match the 650 nm window for PMMA-based POF datacommunications and of interest for the ampli?cation of propagating surface plasmons in plasmonic circuits. DFB lasers fabricated with 1-D gratings exhibit pump pulse energy thresholds as low as 8 nJ (i.e. 26 µJ cm-2 energy- or 2.17 kW cm-2 power-density), lower than many other polymer-based gain media operating in this wavelength range. The con?uence of ef?cient optical gain, relatively high refractive index (aiding optical con?nement) and electronic properties that are conducive to electron injection and transport (F8BT - low lying LUMO) and hole injection and transport (RR-P3HT - high lying HOMO) is relatively novel and is expected to be a necessary (but not sufficient) pre-requisite for any future achievement of electrically pumped lasing. §2. Introduction of the novel concept of conformational meta-materials that utilize the physical geometry (conformation) of a polymer chain segment as the physical structure vector for nanophotonic element definition: Proof of principle demonstration that ß-phase chain segments can be spatially patterned in spin-coated glassy PFO ?lms via masked solvent vapor exposure, thereby leading to a substantial spatial modulation of refractive index. Local optical transmission measurements reveal line pro?les for ?a (absorption change) from which ?n and fraction of ß-phase chain segments can be deduced. For 8.5% ß-phase, ?n ˜ 1.4%, with diffusion defining the feature sizes and (Gaussian) edge pro?les. Our approach preserves a planar ?lm format and does not negatively impact optical gain, both of which are attractive for optoelectronic (photonic lightwave circuit) applications. We specifically demonstrated spatial selection of lasing wavelength for samples in which a ß-phase conformation pattern was induced in a glassy PFO ?lm spin coated atop a 1D DFB grating-etched spectrosil substrate. §3. Influence of PFO:polyethylene blend microstructure on photophysical properties: We have demonstrated that the interplay between PFO concentration and chain conformation, blend microstructure and processing conditions strongly influences the optical anisotropy achievable for PFO in tensile-drawn gel-processed blends with UHMWPE. §4. Gravure printing for inverted structure, solution processed OLEDs: Multilayer polymer (F8BT/TFB) OLEDs fabricated using gravure printed Cs2CO3 electron injection layers (EILs), leading to improved current and power ef?ciency compared to devices in which the EIL was deposited by conventional spin-coating. §5. Advanced ellipsometric characterization of thin film solution processed semiconductors: Careful analysis of the utilization of ellipsometry as a characterization tool to determine anisotropic refractive indices and to determine features of the microstructure. |
| Exploitation Route | Gain media can be utilised in device fabrication and tested for application potential in polymer optical fibre data communication and/or Li-Fi systems. In the latter context some of our collaborators undertook further research in a follow up project to look at this application opportunity. The co-investigators include Professor Dominic O'Brien from Oxford with whom we have initiated discussions about follow-up research. Conformational metamaterials provides a new concept for photonic device fabrication. This is being taken forward in Oxford within Professor Bradley's new research group and with collaborators. A MoU has been subsequently signed with the Materials Science and Engineering Department at the South China University of Technology in Guangzhou (where Professor Ruidong Xia is now based) and further collaborations continue with NanjingTech researchers. In the latter regard we note that Ms Wen Li, Dr Jinyi Lin and Mr Jiang Yi have spent time as visiting students at Imperial College and Oxford to progress research directions initiated under this programme. DDCB has been an Honorary Professor at NanjingTech since 2013 and we established the joint Synergetic Innovation Centre for Advanced Materials (SICAM) between NanjingTech and Imperial College's Centre for Plastic Electronics (CPE)) (2014). The collaboration further supported NanjingTech in applying for the Key Laboratory of Flexible Electronics (2014), a MOST National Center for International Research of Flexible Electronics (2015) and a MOE Joint International Laboratory of Flexible Electronics (2015). Roll-to-roll printing is being used for high-throughput manufacturing of solar cells. Ellipsometry is a widely applicable tool that our results may encourage the wider-use of. |
| Sectors | Digital/Communication/Information Technologies (including Software),Energy,Security and Diplomacy |