Overview
Organic semiconductors are finding their way into an expanding range of applications including light emission, displays, energy conversion, sensors engineering and healthcare. The Centre for Processable Electronics covers organic functional materials, device physics of organic solar cells, manufacturing technologies for large area nano-electronics, and organic LEDs.
Organic Electronic and Optoelectronic Devices
We have achieved breakthroughs in the printing and nanoscale patterning of large-area solution- processed organic electronic devices on plastic. Such devices have use in foldable, wearable and disposable displays, sensors, biomedical devices and other electronics. Working with collaborators in the large-scale integrated EC FP7 POLARIC project, at IIT Milano, and at Imperial, we have used and combined gravure contact printing, zone-refining, nanoimprint lithography and self-alignment techniques to fabricate novel high performance devices. This included a 375 nm channel length high frequency organic transistor operating in the megahertz regime, and complementary inverters with printed dielectric and n- and p- type semiconductors. With colleagues in Chemistry and Materials Science we have developed ambient stable, solution- processable planar and nanostructured metal oxides as high efficiency injection layers in hybrid devices. This included achieving very good compatibility of planar and nanoparticle metal oxides with solution-processed polymer diodes, and demonstrating the first efficient hybrid organic light emitting diodes (OLED) using a zinc oxide nanorod array as a large surface area electron injection layer. Strong progress was also made in developing circularly-polarised light emitting OLEDs in a joint project with CDT Ltd, as well as in the area of printed organic transistors as biomedical sensors.
Soft Electronic Materials Physics
Academic Staff: Professor Ji-Seon Kim
Our research focuses on the basic science and technology of Soft Electronic Materials and Devices (organic semiconductors, organic/inorganic hybrids and bio-nanomaterials), exploring fundamental scientific issues related to using these materials for new optoelectronic applications (Energy, Display and Healthcare). It also parallels with developing Advanced Nanometrology for these materials. Two main research themes in our group are (a) to facilitate the rational design of nanoscale soft functional materials for electronic applications by providing in-depth understanding and control of their nanostructures and optoelectronic properties; (b) to develop advanced spectroscopy techniques that have the unique capability to probe nanoscale non-periodic structures and energetics at soft materials interfaces. Experimental work is accompanied by theoretical simulation. The success of our research program is based on strong collaborative endeavour ranging from materials synthesis, processing, characterisation and device fabrication and modelling, which includes strong collaborations with various national/international universities and industrial partners. Please find more details in the Nanoanalysis Group.
Organic and Hybrid Solar Cells
Academic Staff: Professor Jenny Nelson, Dr Piers Barnes and Dr Jarvist M Frost
Finding new materials to harvest and store solar energy is critical to future clean energy supply. We study the physics, chemistry, materials science and device engineering of new, solution processible materials for solar cells. These include organic semiconductors such as conjugated polymers and small molecules, hybrid inorganic:organic materials and dye sensitised and perovskite materials. The central aim of the group’s research is to understand how chemical structure and physical organisation of materials controls material properties and device function. Our main research activities span:
The device physics of organic and hybrid solar cells: We study the factors controlling current generation and charge recombination in solar cells, such as the role of trap states, doping and interface recombination. We use detailed analysis to determine the sources of loss in practical devices and find ways to reduce such losses.
Property – function relationships in molecular electronic materials: We use a wide range of characterisation techniques to study how material structure controls the processes of light absorption, charge generation and charge transport. A particular goal is to probe the structure of disordered molecular materials, where neutron scattering combined with molecular dynamics has proved useful.
Multi-scale simulation of the electronic and structural properties of organic electronic materials: We have developed methods to simulate the physical structure of materials, and the resulting electronic and optoelectronic properties.
Our long-term aim is the rational design of functional electronic materials. Together with the Grantham Institute for Climate Change, we also research the potential of new renewable technologies to contribute to carbon emissions reductions.
Perovskite Materials Physics
Academic Staff: Dr Piers Barnes, Professor Jenny Nelson and Dr Jarvist M Frost
Hybrid perovskite materials offer the prospect of using cheap precursor solutions to manufacture photovoltaics at low temperature with efficiencies (> 20%) similar to silicon solar cells. Before perovskites can be commercialised several challenges must be overcome, in particular, improving the stability of the materials. Dr. Piers Barnes has discovered that aging of these materials is related to the hysteresis observed in devices where the transient current and voltage characteristics depend on their operational history. We have found that a major degradation pathway is the reversible formation of hydrated phases on exposure to moisture which results in a non- reversible increase in hysteresis. Our neutron scattering studies and modelling show that this hysteresis is unlikely to result from ferroelectric effects which could be coupled to the rotation of methylammonium dipoles in the crystal lattice, and is instead almost certainly related to the migration of ionic defects within the material to screen internal electric fields. We are now developing measurements and simulations that allow us to directly infer the evolution of electric fields within the devices enabling us to understand the influence of ionic migration on hysteresis enabling us to account for some remarkable device behaviour.