Prof. Ifor D.W. Samuel Profile

Prof. Ifor D.W. Samuel

Director Organic Semiconductor Ctr at Univ of St Andrews

SPIE Involvement:

Fellow status | Conference Program Committee | Symposium Chair | Conference Chair | Journal Editorial Board Member | Author | Editor

Area of Expertise:

Organic semiconductor , Organic solar cell , Photophysics , OLED , Organic laser , Biophotonics

Websites:

Company Website

Profile Summary

Professor of Physics and Director of the Organic Semiconductor Centre, University of St Andrews, Scotland. Founder of Ambicare Health Ltd. Regional/Associate editor of Journal of Photonics for Energy, and Synthetic Metals. Fellow of the Royal Society of Edinburgh, SPIE, the Institute of Physics and the Royal Society of Chemistry. I lead a research group exploring the physics of organic semiconductor materials and devices - such as organic light-emitting diodes, solar cells and lasers. The group has particular expertise in photophysics including time resolved luminescence from femtosecond to microsecond timescales and its application to the development of advanced materials such as dendrimers and star-shaped truxenes. In addition I explore emerging applications of organic semiconductors, such as explosive sensing and skin cancer treatment. The work of the centre has been recognised through awards such as the Beilby Medal (Insitute of Materials, Royal Society of Chemistry and Society of the Chemical Industry), the Ben Sturgeon Award (Society for Information Display) and the academic R&D award (from idtechex at Printed Electronics USA). I am co-chair of the Organic Photonics and Electronics symposium at the annual Optics and Photonics meeting in San Diego and on the program committees for several SPIE conferences.

Publications (34)

PROCEEDINGS ARTICLE | May 23, 2018

Deep blue electroluminescence from D-A compounds with oxadiazole acceptor units exhibiting TADF (Conference Presentation)

Proc. SPIE. 10687, Organic Electronics and Photonics: Fundamentals and Devices

KEYWORDS: Organic light emitting diodes, Luminescence, Electroluminescence, Platinum, Phosphorescence, Tablets, Televisions, Light sources and illumination, Display technology, Internal quantum efficiency

In the past few decades Organic Light-Emitting Diodes (OLEDs) have matured to become a widespread display technology. Despite their commercial success in TVs, smartphones and tablet screens, several key issues still remain, especially if OLEDs are to become a viable technology for lighting. Metalorganic emitters based on Ir or Pt are widely used in OLED technology, due to their facile colour tunability, short phosphorescence lifetime and efficient intersystem crossing (ISC), which enables emission from both singlet and triplet states to be harnessed, leading to 100% internal quantum efficiency (IQE). However, these emitters are based on rare and toxic noble metals. In addition, efficient and stable blue and especially deep-blue phosphorescent emitters, which are essential for displays and lighting, are still to be demonstrated in order to replace currently used less efficient fluorescent blue OLEDs. Recently, purely organic emitters exhibiting thermally activated delayed fluorescence (TADF) mechanism were also shown to be capable of 100% IQE. Since efficient ISC in these compounds is based on the small singlet and triplet gap rather than heavy atom effect, TADF compounds represent a new class of potentially inexpensive emitters for next generation OLED displays and lighting. In this work, a series of four deep blue-to-green emitting TADF compounds have been synthesized and characterised. The compounds are based on the same scaffold as the dicarbazoyldicyanobenzene (2CzPN) reported by Adachi and co-workers, but with the replacement of the cyano groups by less electron-withdrawing oxadiazole moieties. The weaker acceptor strength of oxadiazole compared to cyano groups translates to more blue-shifted emission compared to 2CzPN. Additionally, higher spatial separation of HOMO and LUMO levels between acceptor and donor units, respectively, leads to a smaller singlet-triplet gap. This allows us to demonstrate efficient deep blue TADF OLEDs with CIE coordinates (0.16, 0.13), as compared to (0.16, 0.30) for 2CzPN devices. A thorough photophysical study of model compound 2CzPN and oxadiazole acceptor based derivatives will be presented both for solution and thin films. The blue oxadiazole compounds show up 75% quantum yield in solid state. The electrochemical and photophysical properties, as well as crystal structures are compared to the theoretical quantum chemical calculations of the studied compounds. The efficient emission properties coupled to the small singlet-triplet gap in these molecules allows us to demonstrate efficient electroluminescence (up to 10 % EQE) from the vacuum deposited OLEDs.

PROCEEDINGS ARTICLE | May 23, 2018

Improving the thermal stability of OLEDs by doping the electron transport layer with a reactive metal (Conference Presentation)

Proc. SPIE. 10687, Organic Electronics and Photonics: Fundamentals and Devices

KEYWORDS: Thin films, Organic light emitting diodes, Metals, Annealing, Molecules, Crystals, Doping, Atomic layer deposition, Cesium, Electron transport

Organic light-emitting diodes (OLEDs) have reached a huge market as technology for small displays, e.g. in smartphones, and are entering the larger display and solid-state lighting markets as well. In parallel to these commercial successes, the OLED technology is adapted to a multitude of promising new applications, such as in optogenetics and medical therapy. However, it is still challenging to ensure good stability in applications that require high brightness (or high optical power density), in part due to the resulting resistive heating. Increased temperature can lead to a change in morphology of one or several organic layers, e.g. via crystallization of organic molecules, which then reduces electrical and optical performance and likely results in rapid device failure. Aside from an intrinsic resistive heating, heating can also be due to environmental effects during operation or fabrication and encapsulation of devices. For instance, atomic layer deposition (ALD) is a promising technique to form thin, yet highly protective encapsulation layers. However, state-of-the-art ALD processes require relatively high temperature during deposition (< 80 °C). 4,7-diphenyl-1,10-phenanthroline (BPhen) has been widely used as electron transporting layer (ETL) due its high electron mobility, particularly in an organic matrix-dopant system. However, it is well known that thin films of BPhen tend to recrystallize spontaneously. Annealing accelerates crystallization even further due to the relatively low glass transition temperature (Tg) of BPhen (62 °C). A straightforward way to enhance the device thermal stability is to make use of a high Tg material, yet materials have to be carefully adopted to provide appropriate functionality in OLEDs. In this contribution, we report the improvement of the thermal stability of OLEDs with BPhen based electron transport layers (ETLs) by cesium (Cs) doping. To verify the role of the Cs dopant in the BPhen matrix, recrystallization features of Cs-doped BPhen films with different doping concentrations were investigated using optical microscopy and atomic force microscopy. We also examined the photophysical properties of the films, i.e. photoluminescence (PL) and absorption. PL spectra exhibit monotonic red-shifts and broadening as the Cs doping concentration increases. This presumably indicates formation of metal complexes via interaction between the 1,10-phenanthroline group of BPhen molecules and the Cs ions. It was found that Cs plays a critical role, not only in inhibiting undesired recrystallization of BPhen molecules in a thin-film, but also in allowing BPhen layers to be thermally stable beyond the Tg of neat BPhen. Next, the electrical and optical properties of blue and red OLEDs that contain BPhen layers with different Cs-doping concentrations as ETL were characterized after annealing at temperatures between 60 and 100 °C. We find that higher doping concentrations lead to a marked increase in thermal device stability (quantified by current density and luminance at a fixed voltage). Making use of this observation, we successfully encapsulated BPhen based OLEDs with thin-film oxide layers using ALD. The results shown in this work may be transferable to other material systems and can thus provide a useful guideline to enhance the intrinsic thermal durability of organic devices and to render them compatible with processes involving thermal treatment.

PROCEEDINGS ARTICLE | April 21, 2017

Evanescently pumped optofluidic distributed feedback lasers with aqueous gain fluids (Conference Presentation)

Proc. SPIE. 10081, Frontiers in Biological Detection: From Nanosensors to Systems IX

KEYWORDS: Nanosensors, Refractive index, Biosensing, Waveguides, Dispersion, Laser development, Laser marking, Diagnostics, Biological detection systems, Current controlled current source

PROCEEDINGS ARTICLE | January 28, 2017

A comparative study of optical concentrators for visible light communications

Proc. SPIE. 10128, Broadband Access Communication Technologies XI

KEYWORDS: Transmitters, Visible radiation, Eye, Solar concentrators, Modulation, Sensors, Receivers, Optical communications, Compound parabolic concentrators, Wireless communications

SPIE Conference Volume | November 28, 2016

Organic Photovoltaics XVII

SPIE Conference Volume | October 27, 2015

Organic Photovoltaics XVI

SPIE Journal Paper | October 12, 2015

The role of photonics in energy

Zakya Kafafi, Raúl Martín-Palma, Ana Nogueira, Deirdre O’Carroll, Jeremy Pietron, Ifor D. Samuel, Franky So, Nelson Tansu, Loucas Tsakalakos

JPE Vol. 5 Issue 01

KEYWORDS: Solar cells, Solar energy, Photonics, Organic light emitting diodes, Semiconductors, Electrons, Light emitting diodes, Silicon, Photons, Thin films

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SPIE Journal Paper | June 12, 2015

Organic solar cells based on acceptor-functionalized diketopyrrolopyrrole derivatives

Sanjay S. Ghosh, Luis Serrano, Bernd Ebenhoch, Vincent Rotello, Graeme Cooke, Ifor D. Samuel

JPE Vol. 5 Issue 01

KEYWORDS: Solar cells, Annealing, Organic photovoltaics, Absorption, Magnesium, Atomic force microscopy, Electrodes, Resistance, Molecules, External quantum efficiency

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SPIE Conference Volume | November 5, 2014

Organic Photovoltaics XV

PROCEEDINGS ARTICLE | March 29, 2013

Formation of quantum dots from precursors in polymeric films by ps-laser

Proc. SPIE. 8607, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XVIII

KEYWORDS: Laser therapeutics, Polymers, Luminescence, Composites, Quantum dots, Transmission electron microscopy, Laser irradiation, Cadmium sulfide, Picosecond phenomena, Polymer thin films

PROCEEDINGS ARTICLE | September 13, 2012

Strongly modified angular dependence of emission from OLEDs

Proc. SPIE. 8476, Organic Light Emitting Materials and Devices XVI

KEYWORDS: Surface plasmons, External quantum efficiency, Scattering, Organic light emitting diodes, Light scattering, Electroluminescence, Nanoimprint lithography, Waveguide modes, Europium, Optical microcavities

PROCEEDINGS ARTICLE | September 13, 2012

Nanoimprinted resonators for polymer lasers pumped by light-emitting diodes

Proc. SPIE. 8476, Organic Light Emitting Materials and Devices XVI

KEYWORDS: Light emitting diodes, Nanostructuring, Resonators, Polymers, Silicon, Photonic crystals, Semiconductor lasers, Laser resonators, Laser damage threshold, Nanolithography

PROCEEDINGS ARTICLE | September 17, 2011

Conjugated polymer sensors for explosive vapor detection

Proc. SPIE. 8118, Organic Semiconductors in Sensors and Bioelectronics IV

KEYWORDS: Explosives detection, Sensors, Polymers, Luminescence, Molecules, Nitrogen, Explosives, Signal detection, Quenching (fluorescence), Polymeric sensors

PROCEEDINGS ARTICLE | August 21, 2009

Hybrid organic-inorganic POSS dendritic materials: photoluminescence chromophore control via confinement and steric hindrance

Proc. SPIE. 7396, Physical Chemistry of Interfaces and Nanomaterials VIII

KEYWORDS: Luminescence, Molecules, Silicon, Quantum efficiency, Nitrogen, Chemistry, Chromophores, Absorbance, Dendrimers, Temperature metrology

PROCEEDINGS ARTICLE | September 2, 2008

Light-emitting poly(dendrimer)s

Proc. SPIE. 7051, Organic Light Emitting Materials and Devices XII

KEYWORDS: Magnesium, Organic light emitting diodes, Polymers, Luminescence, Printing, Polymerization, Dendrimers, Chromatography, Inkjet technology, Absorption

PROCEEDINGS ARTICLE | September 2, 2008

Light-emitting diode pumped polymer lasers

Proc. SPIE. 7051, Organic Light Emitting Materials and Devices XII

KEYWORDS: Semiconductors, Light emitting diodes, Organic light emitting diodes, Polymers, Semiconductor lasers, Laser resonators, Laser damage threshold, Indium gallium nitride, Pulsed laser operation, Polymer thin films

PROCEEDINGS ARTICLE | May 1, 2008

An organic semiconductor laser on silicon

Proc. SPIE. 6996, Silicon Photonics and Photonic Integrated Circuits

KEYWORDS: Mirrors, Resonators, Silica, Polymers, Silicon, Reflectivity, Semiconductor lasers, Laser damage threshold, Organic semiconductors, Hybrid silicon lasers

PROCEEDINGS ARTICLE | October 16, 2007

Diode-pumped polymer lasers

Proc. SPIE. 6655, Organic Light Emitting Materials and Devices XI

KEYWORDS: Mirrors, Resonators, Polymers, Luminescence, Energy transfer, Semiconductor lasers, Diodes, Laser damage threshold, Polymer thin films, Absorption

PROCEEDINGS ARTICLE | September 26, 2007

Shrinking polymer lasers

Proc. SPIE. 6713, Nanophotonics and Macrophotonics for Space Environments

KEYWORDS: Semiconductors, Mirrors, Polymers, Luminescence, Energy transfer, Semiconductor lasers, Photonics, Laser damage threshold, Polymer thin films, Absorption

PROCEEDINGS ARTICLE | December 5, 2006

Phosphorescent iridium(III) cored dendrimers for light-emitting displays

Proc. SPIE. 6333, Organic Light Emitting Materials and Devices X

KEYWORDS: Light emitting diodes, External quantum efficiency, Organic light emitting diodes, Polymers, Luminescence, Molecules, Diffusion, Excitons, Dendrimers, Absorption

PROCEEDINGS ARTICLE | November 15, 2006

Exciton annihilation and diffusion in semiconducting polymers

Proc. SPIE. 6334, Organic Photovoltaics VII

KEYWORDS: Semiconductors, Organic photovoltaics, Polymers, Annealing, Solar cells, Luminescence, Diffusion, Absorbance, Excitons, Picosecond phenomena

PROCEEDINGS ARTICLE | October 10, 2005

Highly branched phosphorescent dendrimers

Proc. SPIE. 5937, Organic Light-Emitting Materials and Devices IX

KEYWORDS: Magnesium, Argon, Luminescence, Quantum efficiency, Chromophores, Dendrimers, Solid state physics, Chromatography, Absorption, Oxidation

PROCEEDINGS ARTICLE | October 9, 2005

Novel diffractive feedback structures for semiconducting polymer lasers

Proc. SPIE. 5937, Organic Light-Emitting Materials and Devices IX

KEYWORDS: Semiconductors, Diffraction, Modulation, Resonators, Scattering, Polymers, Semiconductor lasers, Laser damage threshold, Modes of laser operation, Diffraction gratings

PROCEEDINGS ARTICLE | October 8, 2005

Semiconducting polymer optical amplifiers

Proc. SPIE. 5937, Organic Light-Emitting Materials and Devices IX

KEYWORDS: Semiconductors, Optical fibers, Optical amplifiers, Polymers, Luminescence, Laser beam diagnostics, Solid state electronics, Organic semiconductors, Optical semiconductors, Absorption

PROCEEDINGS ARTICLE | February 16, 2004

Conjugated dendrimers: a modular approach to materials for full-color displays

Proc. SPIE. 5214, Organic Light-Emitting Materials and Devices VII

KEYWORDS: Eye, Light emitting diodes, External quantum efficiency, Organic light emitting diodes, Polymers, Molecules, Electroluminescence, Chromophores, Dendrimers, Luminous efficiency

PROCEEDINGS ARTICLE | September 17, 2002

Efficient solution-processed dendrimer OLEDs

Proc. SPIE. 4918, Materials, Devices, and Systems for Display and Lighting

KEYWORDS: Energy efficiency, Optical lithography, Organic light emitting diodes, Polymers, Molecules, Interfaces, Coating, Physics, Dendrimers, Electro optics

PROCEEDINGS ARTICLE | June 13, 2002

Photonic band structure and emission characteristics of a metal-backed polymeric distributed feedback laser

Proc. SPIE. 4642, Organic Photonic Materials and Devices IV

KEYWORDS: Light emitting diodes, Scattering, Organic light emitting diodes, Polymers, Metals, Luminescence, Silver, Reflectivity, Laser damage threshold, Waveguide modes

PROCEEDINGS ARTICLE | February 2, 2001

Electroluminescent devices incorporating a new oxadiazole derivative

Proc. SPIE. 4105, Organic Light-Emitting Materials and Devices IV

KEYWORDS: Light emitting diodes, Electrodes, Metals, Copper, Interfaces, Quantum efficiency, Electroluminescence, Aluminum, Electron transport, Information operations

PROCEEDINGS ARTICLE | December 17, 1999

Device model for polymer light-emitting diodes: effect of temperature and oxidation

Proc. SPIE. 3797, Organic Light-Emitting Materials and Devices III

KEYWORDS: Light emitting diodes, Organic light emitting diodes, Polymers, Indium, Aluminum, Temperature metrology, Instrument modeling, Tin, Absorption, Oxidation

PROCEEDINGS ARTICLE | December 17, 1999

Photoluminescence studies of the light-emitting species in new materials for polymer devices

Proc. SPIE. 3797, Organic Light-Emitting Materials and Devices III

KEYWORDS: Thin films, Data modeling, Polymers, Spectroscopy, Luminescence, Dielectrics, Quantum efficiency, Chemistry, Polymer thin films, Absorption

PROCEEDINGS ARTICLE | December 17, 1999

Effect of generation on the electronic properties of light-emitting dendrimers

Proc. SPIE. 3797, Organic Light-Emitting Materials and Devices III

KEYWORDS: Thin films, Light emitting diodes, External quantum efficiency, Electrodes, Polymers, Luminescence, Dendrimers, Solid state physics, Electron transport, Chromatography

PROCEEDINGS ARTICLE | December 1, 1997

Photoluminescence in poly(3-hexylthiophene)

Proc. SPIE. 3145, Optical Probes of Conjugated Polymers

KEYWORDS: Thin films, Polymers, Luminescence, Molecules, Quantum efficiency, Excimers, Excitons, Picosecond phenomena, Polymer thin films, Absorption

PROCEEDINGS ARTICLE | December 1, 1997

Polypyridine as an efficient electron-transporting polymer for light-emitting diodes

Proc. SPIE. 3148, Organic Light-Emitting Materials and Devices

KEYWORDS: Light emitting diodes, External quantum efficiency, Electrodes, Organic light emitting diodes, Polymers, Electrons, Calcium, Electroluminescence, Diodes, Aluminum

PROCEEDINGS ARTICLE | December 1, 1997

Photophysical characterization of poly(p-pyridine)

Proc. SPIE. 3145, Optical Probes of Conjugated Polymers

KEYWORDS: Thin films, Light emitting diodes, Polymers, Luminescence, Quantum efficiency, Nitrogen, Electroluminescence, Excimers, Solid state physics, Absorption

Showing 5 of 34 publications

Conference Committee Involvement (39)

Optical Materials and Biomaterials in Security and Defence Systems Technology

9 September 2019 | Strasbourg, France

Organic and Hybrid Sensors and Bioelectronics XII

11 August 2019 | San Diego, California, United States

SPIE Organic Photonics + Electronics

11 August 2019 | San Diego, United States

Organic, Hybrid, and Perovskite Photovoltaics XX

11 August 2019 | San Diego, California, United States

Organic and Hybrid Light Emitting Materials and Devices XXIII

11 August 2019 | San Diego, California, United States

Showing 5 of 39 published special sections

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