We work with a wide range of materials for use in OLEDs, solar cells and organic electronic devices.

Polymers

Plastic polymeric materials contain a very long series of repeat units of a monomer. When the unit is composed of a conjugated carbon chain then the material, rather than behaving like a traditional plastic insulator, instead can show light emitting and semiconducting properties.

Conducting polymers, first discovered by Heerger, MacDiarmid and Shirakawa in 1977, have been found to be implementable in organic light emitting diodes (OLED) (Burroughes et al. 1990) and organic thin film solar cells.

We work with a diverse range of polymer materials, studying their properties to tune advantageous properties for devices.

Small Molecules

Small molecule organic semiconducting materials have long been studied for their interesting novel properties. The discovery by Tang and Van Slyke of the light emitting OLED material Alq3 in 1987 raised the interest in these materials. Development of small molecule organic semiconductors was further enhanced by the discovery of triplet sensitisation for use in organic solar cells by O'Regan and co-workers in 1991 and the discovery of suitable phosphorescent emitters for use in OLEDs by Baldo et al. in 1998.

We work with a large range of small molecule materials for use both in OLED, solar cell and organic electronic devices

Dendrimers

The advantageous properties of polymer materials (solution processability) and of small molecule systems (potentially near 100% internal efficiency due to phosphorescence) have been combined by Ifor Samuel and Paul Burn with the invention of dendrimer materials for OLEDs. These large branching materials allow fine control of the emissive properties while, independently, also allowing control of the environmental properties for optimisation of devices.

We have explored and continue to investigate the novel properties of these highly branched materials for use in a wide range of organic semiconductor applications.



Characterisation

All of these materials can be characterised using the equipment in our group. To understand the physics occurring in these systems, and to better control and optimise parameters for best device results requires the use of a number of techniques.

We can:

• Take steady state absorption and luminescence spectra to understand the emissive properties of the material

• Record the internal efficiency of the compound (called the photoluminescence quantum yield, PLQY) to determine whether a material is a good emitter.

• To characterise that emission in the time-domain we can use a number of setups to record the kinetics. Time correlated single photon counting (TCSPC) can give single wavelength dynamics while a time-gated CCD can give broad-band dynamics. If higher time resolution is required then the femtosecond and picosecond kinetics can be recorded using setups in our femtolab.

• Upon depositing the material on a substrate we can perform surface profiling with our AFM or DEKTAK profiler to determine the quality of the film and any structures that have been patterned onto it.