Ross D. Jansen-van Vuuren

Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes

Spectrally selective light detection is vital for full-colour and near-infrared (NIR) imaging and machine vision. This is not possible with traditional broadband-absorbing inorganic semiconductors without input filtering, and is yet to be achieved for narrowband absorbing organic semiconductors. We demonstrate the first sub-100 nm full-width-at-half-maximum visible-blind red and NIR photodetectors with state-of-the-art performance across critical response metrics. These devices are based on organic photodiodes with optically thick junctions. Paradoxically, we use broadband-absorbing organic semiconductors and utilize the electro-optical properties of the junction to create the narrowest NIR-band photoresponses yet demonstrated. In this context, these photodiodes outperform the encumbent technology (input filtered inorganic semiconductor diodes) and emerging technologies such as narrow absorber organic semiconductors or quantum nanocrystals. The design concept allows for response tuning and is generic for other spectral windows. Furthermore, it is material-agnostic and applicable to other disordered and polycrystalline semiconductors.

Organic Photodiodes: The Future of Full Color Detection and Image Sensing

Major growth in the image sensor market is largely as a result of the expansion of digital imaging into cameras, whether stand-alone or integrated within smart cellular phones or automotive vehicles. Applications in biomedicine, education, environmental monitoring, optical communications, pharmaceutics and machine vision are also driving the development of imaging technologies. Organic photodiodes (OPDs) are now being investigated for existing imaging technologies, as their properties make them interesting candidates for these applications. OPDs offer cheaper processing methods, devices that are light, flexible and compatible with large (or small) areas, and the ability to tune the photophysical and optoelectronic properties - both at a material and device level. Although the concept of OPDs has been around for some time, it is only relatively recently that significant progress has been made, with their performance now reaching the point that they are beginning to rival their inorganic counterparts in a number of performance criteria including the linear dynamic range, detectivity, and color selectivity. This review covers the progress made in the OPD field, describing their development as well as the challenges and opportunities.

Colour selective organic photodetectors utilizing ketocyanine-cored dendrimers

Accurate colour reproduction by image sensors requires four narrow-band absorbing photodetectors (blue, green, yellow and red), and this is generally achieved by using a broadband photodetector and colour filters. We have developed an organic photodetector in which colour selection is achieved by the light-absorbing layer of the detector. The photoactive layer is comprised of a green absorbing ketocyanine dye-cored dendrimer with the dendrons providing solution processability and prevention of aggregation in the solid-state, which can otherwise lead to the broadening of the absorption spectrum. The properties of the photoactive dendrimer were found to be dependent on the attachment point and number of dendrons. The best photodetector contained a bulk heterojunction (BHJ) light-absorbing layer comprised of the dendrimer with two first generation biphenyl-based dendrons attached to the nitrogen atoms of the ketocyanine dye blended with [6,6]-phenyl-C61-butryic acid methyl ester (PC60BM). The photodetector had a Full Width at Half Maximum (FWHM) of the response of 130 nm centred around 500 nm, an External Quantum Efficiency (EQE) of 8.2% at −1 V and the largest rectification ratio (2.7 × 104 at 0 V) so far reported for a green-absorbing organic photodetector. The performance of the photodetector was found to be approaching that required for current machine vision systems.

Photo‐Rechargeable Battery Effect in First Generation Cationic‐Cyanine Dendrimers

A photobattery based on a cationic cyanine dendrimer is demonstrated. The battery can be recharged simply by exposure to light. The mechanism for charge storage and discharge is proposed.

An external quantum efficiency of >20% from solution-processed poly(dendrimer) organic light-emitting diodes

Controlling the orientation of the emissive dipole has led to a renaissance of organic light-emitting diode (OLED) research, with external quantum efficiencies (EQEs) of >30% being reported for phosphorescent emitters. These highly efficient OLEDs are generally manufactured using evaporative methods and are comprised of small-molecule heteroleptic phosphorescent iridium(III) complexes blended with a host and additional layers to balance charge injection and transport. Large area OLEDs for lighting and display applications would benefit from low-cost solution processing, provided that high EQEs could be achieved. Here, we show that poly(dendrimer)s consisting of a non-conjugated polymer backbone with iridium(III) complexes forming the cores of first-generation dendrimer side chains can be co-deposited with a host by solution processing to give highly efficient devices. Simple bilayer devices comprising the emissive layer and an electron transport layer gave an EQE of >20% at luminances of up to ≈300 cd/m2, showing that polymer engineering can enable alignment of the emissive dipole of solution-processed phosphorescent materials.Efficient OLEDs from solution: engineering dipole alignment in polymersDipole alignment is achieved in efficient solution-processed organic light-emitting diodes featuring a novel poly(dendrimer). A collaborative team led by Paul Burn from the Centre for Organic Photonics & Electronics, School of Chemistry & Molecular Biosciences at The University of Queensland have developed solution-processed organic light-emitting diodes (OLEDs) based on a phosphorescent poly(dendrimer)-based material with an out-coupling efficiency of around 40% and an external quantum efficiency of above 20%. The key to the enhanced light out-coupling in the devices is the favourable alignment of emissive dipoles in the poly(dendrimer), which consists of dendritic side-chains comprised of hole-transporting carbazole-based dendrons and iridium(III) complex-cores. The poly(dendrimer) is blended with a host material to ensure high efficiency in the device. Ultimately, the intelligent design of the developed poly(dendrimers) allowed the authors to utilise a simple bilayer device structure to demonstrate highly efficient solution-processed organic light-emitting diodes.

The Development of Dendronized Polymers Containing Phosphorescent Iridium(III) Complexes for Solution-processable OLED Devices

Polymers containing pendant iridium(III) complexes encapsulated within carbazole-based dendrons were prepared. Their design and photophysical and optoelectronic properties are presented in the context of applications within flexible lighting modules.