Within light sensing optoelectronic devices, multijunction organic and hybrid photodetectors show a large potential. In particular, organic and hybrid phototransistors hold promises for high-sensitivity thanks to their inherent signal-amplification characteristics. However, often a trade-off between a large sensing area, a fast response, and a high specific detectivity is difficult to be achieved. Here we propose an alternative phototransistor concept, that relies on a geometrically engineered large area tri-channel architecture, applied to a multilayer hybrid phototransistor composed of an inorganic In2O3/ZnO n-type field-effect channel, and a top organic bulk-heterojunction or hybrid perovskite light-sensing layer. Up-scalable solution-processing of both the field-effect channel and the light-sensing layers are implemented. Different photoactive layers are used to corroborate and validate the proposed concept. The resulting phototransistor combines the characteristics of easy solution processing, a maximum responsivity of 10^5 A/W thanks to the large electron mobility of the In2O3/ZnO heterointerface, and a maximum specific detectivity of 10^15Jones (at a low gate voltage of 5V and under a low light illumination of 10 nW/cm2), thanks to the large sensing area which is fully exploited in the tri-channel architecture. The improved photoresponse characteristics are accompanied by a fast response (risetime <10ms down to the uW/cm2 of illumination), which is comparable to the time-response of analogous phototransistors in the conventional architecture. The experimental data are supported by device modelling, which helps highlighting the peculiar advantages of the proposed large area, tri-channel and multi-junction phototransistor architecture.
Organic and metal-halide perovskites semiconductors share many attractive attributes for application in an expanding range of emerging opto-electronics. However, extensive efforts to translate their advantageous characteristics to viable commercial technologies, have highlighted the numerous technological challenges that still remain. In this presentation I will discuss our recent efforts to address some of these challenges by combining perovskites with organic semiconductors. I will show how physical blending of the two components in combination with other building blocks borrowed from printed electronics, can lead to prototypical devices, such as transistors, memories, and memristors, with intriguing functionalities and performance.
In recent years, nano, opto, and bio-electronics have seen rapid advancements due to improved fabrication tools. Devices in these fields require functional structures with arbitrary patterns and feature sizes ≤100 nm. Although commercial extreme UV lithography has the potential to fabricate these nanoscale patterns, economic and technological factors limits their up-scalable manufacturing. Here we report a low-cost, large-area compatible mass-manufacturing method to produce moulds and consecutively soft-stamps with nanoscale features. The method relies on the use of our technique called adhesion lithography (a-lith)1 to realize moulds of patterned metal electrodes which are separated laterally by a distance (length) that can range between 1-100 nm. The lateral size of these electrodes (width), on the other hand, can vary from hundreds of nanometers to meters. Soft stamps, which can be used to replicate multiple copies of high aspect ratio planar nanoscale patterns on arbitrary substrates, were successfully prepared from such a mould. Further, the same nanogap metal electrodes made from a-lith used as a mask to etch the underneath Si substrate, resulting in nanofluidic channels used for bio-applications such as DNA and bio-molecule imaging and sensing.
In this talk I will discuss key recent developments in the field of OPVs with focus on practical strategies for boosting the overall cell performance. Particular emphasis will be placed on the use of electronic dopants and advanced interlayer technologies for improving the cell’s efficiency and operational stability. Finally, the design and implementation of multi-junction cell architectures will be discussed.
5G networks are currently being deployed around the world, introducing a new era in machine-to-machine communications and reinforcing the Internet of Things. The 5G radiofrequency bands range from sub-1 GHz to 70 GHz, while the 6th generation (6G) is expected to cover bands at hundreds of GHz. There is a need for devices with high frequency performance and scalable manufacturing using inexpensive techniques and materials. Herein we present ZnO-based Schottky diodes, processed from solution on wafer scale with high yield. Coplanar nanogap electrodes are fabricated using a high-throughput low-cost technique, named adhesion lithography. The diodes’ cutoff frequency exceeds 100 GHz.
Tandem structure provides a practical way to realize high efficiency organic photovoltaic (OPV) cells due to the limited optical absorption in organic semiconductors and tandem cells can be used to extend the wavelength coverage of the solar spectrum for light harvesting. The interconnecting layer (ICL) between subcells in a tandem solar cell plays a critical role in the reproducibility and the performance of tandem devices, and the processability of the ICL in a tandem cell has been a challenge. In this work we report on the fabrication of highly reproducible high efficiency tandem cells by employing a commercially available material, PEDOT:PSS HTL Solar (HSolar), as the hole transporting material used for the ICL. Comparing with the conventional PEDOT:PSS Al 4083, HSolar offers a better wettability on the underlying non-fullerene photoactive layers, resulting in better charge extraction properties of the ICL. When FTAZ:IT-M and PTB7-Th:IEICO-4F are used as the front cell and the back cells to fabricate the tandem solar cells, a power conversion efficiency (PCE) of 14.7% is achieved. To validate the processability of these tandem cells, three other research groups have successfully fabricated tandem cells using the same recipe and the highest PCE obtained is 16.1%. With further development of donor polymers and device optimization, our device simulation results show that a PCE < 22% can be realized in tandem cells in the near future.
Harnessing the omnipresent radio frequency (RF) waves intend to explore the new diode technologies as they determine the frequency of operation and ultimately the power conversion efficiency. Recently, a considerable effort focused on performance, reliable and low-cost fabrication methods. Here, we report the fabrication of sub-20 nm co-planar, asymmetric and self-forming nanogap electrodes by adhesion lithography (a-Lith) as an alternative, low-cost and large-area patterning technique. Moreover, solution processing and rapid Flash Lamp Annealing (FLA) route employed to fabricate Schottky diodes. These diodes are having more than 104 On/Off ratio, low series resistance and junction capacitance due to the novel co-planar architecture and thus operating beyond 10 GHz. This paves the way to a radically new diode technology that has a huge impact on the IoT – Wireless Energy Harvesting (WEH) and RFID system.
Nanoscale optoelectronic devices based on coplanar nanogap electrodes, when compared with traditional vertical devices, exhibit attractive characteristics, such as high density of integration, high sensitivity, fast response and multifunctionality. Moreover, their low-cost high-throughput fabrication on flexible disposable substrates opens up several new applications in sectors ranging from telecommunications and consumer electronics to healthcare - to name a few. However, their commercial exploitation has been hitherto impeded by technological bottlenecks, owing to the incompatibility of currently available fabrication techniques, eg. e-beam lithography, with industrial upscaling.
Adhesion lithography is a nanopatterning technique that allows the facile high yield fabrication of coplanar metal electrodes separated by a sub-15 nm gap on large area substrates of any type, including plastic. These electrodes, when combined with solution-processed and/or low-dimensional nanostructured materials deposited at low, plastic-compatible, temperatures give rise to nanoscale optoelectronic devices with intriguing properties.
It will be shown that both nanoscale light-emitting and light-sensing devices can be fabricated upon using light-emitting polymers along with self-assembling surface modifiers, and lead halide perovskites and functionalised colloidal PbS quantum dots, respectively. Emphasis will be given in recent advances in flexible nanoscale photodetectors fabricated with nanogap coplanar electrodes, operating in DUV up to NIR part of the spectrum. These devices exhibit high responsivity, sensitivity and fast response speed (hundreds of nanoseconds) owing to the extreme downscaling of key device dimensions. These results demonstrate that adhesion lithography combined with advanced materials concepts constitutes a new fabrication paradigm enabling a plethora of advanced applications within the field of flexible electronics.
We present the synthesis and characterization of four conjugated polymers containing a novel chromophore for organic electronics based on an indigoid structure. These polymers exhibit extremely small band gaps of ∼1.2 eV, impressive crystallinity, and extremely high n-type mobility exceeding 3 cm2 V s–1. The n-type charge carrier mobility can be correlated with the remarkably high crystallinity along the polymer backbone having a correlation length in excess of 20 nm. Theoretical analysis reveals that the novel polymers have highly rigid nonplanar geometries demonstrating that backbone planarity is not a prerequisite for either narrow band gap materials or ultrahigh mobilities. Furthermore, the variation in backbone crystallinity is dependent on the choice of comonomer. We find that electron mobility can be correlated to the degree of order along the conjugated polymer backbone. Finally, we use this novel system to begin to understand the complicated effect of alkyl chain variation on the solid state packing in all 3 dimensions.
The commercial interest in Radio Frequency Identification (RFID) tags keeps growing, as new application sectors, spanning from healthcare to electronic article surveillance (EAS) and personal identification, are constantly emerging for these types of electronic devices. The increasing demand for the so-called “smart labels” necessitates their high throughput manufacturing, and indeed on thin flexible substrates, that will reduce the cost and render them competitive to the currently widely employed barcodes.
Adhesion Lithography (a-Lith) is a novel patterning technique that allows the facile high yield fabrication of co-planar large aspect ratio (<100,000) metal electrodes separated by a sub-20 nm gap on large area substrates of any type. Deposition of high mobility semiconductors from their solution at low, compatible with plastic substrates, temperatures and application of specific processing protocols can dramatically improve the performance of the fabricated Schottky diodes.
It will be shown that in this manner both organic and inorganic high speed diodes and rectifiers can be obtained, operating at frequencies much higher than the 13.56 MHz benchmark, currently employed in passive RFID tags and near filed communications (NFC). This showcases the universality of this method towards fabricating high speed p- and n-type diodes, irrespective of the substrate, simply based on the extreme downscaling of key device dimensions obtained in these nanoscale structures. The potential for scaling up this technique at low cost, combined with the significant performance optimisation and improved functionality that can be attained through intelligent material selection, render a-Lith unique within the field of plastic electronics.
Plastic electronics that can be manufactured using solution-based methods are the subject of great research interest due to their potential for low-cost, large-area electronic applications. The interest in this field has led to considerable research and subsequent advances in device performance. To this end solution-processed organic thin-film transistors (OTFTs) have shown impressive improvements in recent years through the increasing values of charge carrier mobility. Here we report the development of next generation organic blend materials for OTFTs with hole mobilities of 10 cm2/Vs. These high performance devices have been achieved using a novel semiconducting blend system comprising of an amorphous-like conjugated polymer and a high mobility small molecule. The combination of a highly crystalline small molecule with the polymer binder aids the formation of uniform films as well as enables an element of control over the nucleation and growth of the small molecule. The polymer binders investigated belongs to the family of indacenodithiophene-based copolymers which are renowned for their high carrier mobilities regardless of their apparent structural disorder. The addition of the polymer with carefully chosen small molecules is found to further increase the hole mobility of the resulting blend OTFT to over 10 cm2/Vs. These organic devices provide an interesting insight into this rather complex blend system, highlighting the correlation between the morphology developed following solution processing and device performance, as well as exploring the role of each of the two components in the blend in terms of their contribution to charge transport.
Novel, extremely narrow band-gap polymer with a structure based on natural indigo has been synthesised and exhibits high crystallinity, high ambipolar transport in OFET devices, and OPV device efficiencies up to 2.35% with light absorbance up to 950 nm, demonstrating potential in near-IR photovoltaics. We demonstrate that the use of a potentially bio-sustainable monomer unit in a conjugated polymer can give balanced ambipolar OFET mobilities in excess of 0.5 cm2/Vs. This novel monomer, and polymers are synthesized by rigidifying the structure of indigo by condensation with an aromatic acidic acid. The materials display high crystallinity which can be further enhanced by annealing and demonstrate that it can be used as a potentially biosustainable alternative to the commonly used DPP and iso-indigo monomers. We believe this is the first attempt to tackle the issue of sustainability in conjugated polymer synthesis.
Herein we present an extension of our work on indacenodithiophenes (IDT) by replacing the central benzene ring
with a thieno(3,2-b) thiophene unit. This newly developed thieno[3,2-b]thieno bisthiophene (4T) donor moiety was
synthesized from commercially available reagents and incorporated into a series of donor-acceptor polymers. We
will discuss the pronounced donating character of 4T compared to IDT and the choice of bridging atom in those
new polymers with an emphasis on field effect transistor and photovoltaic device performance.
Reduction in the operating voltage of organic field-effect transistors (OFETs) is sought for their successful
implementation into future portable and low-power electronic applications. Here we demonstrate OFETs with operation
below 2 V enabled by the use of self-assembled monolayer (SAM) gate dielectrics with high geometrical capacitances. A
high surface energy monolayer is chosen to allow processing of small molecule semiconductors from solution.
Impedance spectroscopy measurements of metal-insulator-semiconductor devices suggest the geometrical capacitance of
the alumina-SAM dielectric can reach ~1 μF/cm2 when accumulating charge at the semiconductor-insulator interface.
Atomic force microscopy images reveal that the glass substrates and the SAM-functionalized aluminum gate electrode
display significant roughness. Despite this, mobilities of 0.02 cm2/Vs are demonstrated. These results represent an
important step towards low-power solution processable electronics.
Since their invention use of organic field-effect transistors (OFETs) has been restricted to applications that explore their
unifunctional, i.e. current switching, characteristics. Recently, however, OFETs with additional functionalities have been
designed and demonstrated with most notable examples the light-emitting (LE-OFET)[1] and light-sensing (LS-OFET)[2]
transistors. These devices are of particular significance since design and fabrication of a new type of organic circuits can
now be envisioned. Here we report on electro-optical circuits based on ambipolar LS-OFETs and unipolar OFETs. By
carefully tuning the ambipolar transport of LS-OFETs their photosensitivity can be controlled and optimised. By going a
step further and integrating LS-OFETs with unipolar OFETs we are able to demonstrate various optoelectronic circuits
including electro-optical switches and logic gates. A unique characteristic of these gates is that their input signal(s) can
be designed to be either all-optical or electro-optical. An additional advantage of the technology is that LS-OFETs can be
integrated with the driving electronics using the same number of processing steps, hence eliminating the need of
additional fabrication costs. This is one of the first demonstrations of organic circuits where signal processing involves
the use of both optical and electrical input signals. Such optoelectronic devices/circuits could one day be explored in
various applications including electro-optical transceivers and optical sensor arrays.
Conjugated dendrimers provide an excellent molecular architecture for tuning material properties for organic light emitting diodes. Here we demonstrate a modular approach allowing highly efficient fluorescent and phosphorescent emissive chromophores to be used to make red, green and blue solution-processed light emitting diodes. The choice of a common dendritic architecture ensures good solubility and film forming properties irrespective of the choice of core unit. In addition, this architecture allows blending of dendrimers with different cores without phase separation. We show that blending provides a simple but powerful way of tuning the color of dendrimer LEDs from deep blue to blue-green, and from green to red with little impact on the device properties.
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