Tailoring organic semiconductors for photonics: photophysics and device exploitation from bio-theranostics to visible light communications (VLCs) and photovoltaics

Dr Franco Cacialli
University College London
Industry Co-Sponsor
ISIS Neutron and Muon Source
Project Description
The project will strategically exploit the synergy in the synthesis (ICL) and optical characterisation/device exploitation (ICL) in the area of low-gap semiconductors. These are the active components of near-infrared (NIR) emitting devices, and vital to achieving high power conversion efficiency (PCE) OPVDs. NIR emitters are attracting burgeoning interest because of their potential for applications in areas as diverse as security, biomedicine (photodynamic therapy, biosensing etc. due to the NIR semitransparency of biological tissue), visible light communications (VLCs) and therefore application to the internet-of-things (IoT), and even horticulture. Low-gap absorbing materials are crucial to extending the spectral range of operation of solar cells and thus for optimising their PCE.

The project builds on recent interaction between the PIs on a naphthalene diimide (NDI) polymeric derivative with surprising properties.

Specific research open questions to be addressed:

(a) Is it possible to achieve aggregation/crystallization-induced emission (AIE/CIE) with novel NDI derivatives rather than tetra-phenyl ethylene (TPE) moieties?

(b) What is the role of aggregation vs. Energy-gap law in limiting the photoluminescence quantum yields (PLQYs) of low-gap materials in general and in particular of NDI derivatives?

(c) what is the best strategy to boost the PLQY of NDI-based chromophores?

(d) What is the advantage of the NDI high PLQY derivative for organic solar cells?

(e) Find the most effective device architecture for exploiting the photovoltaic (PV) properties of NDIs (e.g. binary or ternary blend, direct inverted structure).

Questions (a)-(c) will be addressed by a combination of optical spectroscopy and light-emitting devices fabrication/characterisation (OLEDs, OLETs, LECs).

Key Techniques
•Chemical/structural characterisation: NMR/mass spectrometry for chemical characterisation;XRD (GIWAX), differential scanning calorimetry (DSC) and atomic force microscopy (AFM) for solid state structure;
temperature dependent UV-Vis, light scattering and neutron scattering for solution aggregation/assembly behaviour.

•Optical/device characterisation: time-resolved photoluminescence (TCSPC), PLQY, ellipsometry, incorporation in OLEDs, OLETs, LECs, OPVDs, and characterisation of their luminance/radiance/external quantum efficiency (EQE) and of their photovoltaic action (PCE, EQE). Electroabsorption spectroscopy.

For information on how to apply for this project please visit cdt-acm.org/phd-opportunities

Elwin Hunter

Studying my PhD as part of the ACM CDT not only provided me with valuable training courses and workshops on characterisation techniques, but also regular academic seminars, team activities, and discussions to help expand my interests, both inside and outside of research.