CACIALLI4	Growth and characterisation of single crystals of organic semiconductors
Type	Experimental
#students	1
Orientation	Why is the scientific problem of interest at all? Achieving large, high-quality, and solvent-free crystals of applications-relevant organic semiconductors is crucial to affording ever more detailed insights into the fundamental charge and exciton physics underpinning the technology of photovoltaic diodes (PVDs), field-effect transistors (FETs), and light-emitting diodes (LEDs).
How	How is the research going to shed light on the given problem?. In our group, we have recently^1 developed a reproducible method for growth of large, high-quality, and solvent-free crystals of small-molecular weight organic semiconductors (OS) such as [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) (see figure below). PCBM is a derivative of C60 with enhanced solubility in organic solvent that has gained an unparalleled role as the electron acceptor of choice in organic solar cells. The ability to prepare solvent-free crystals is the crucial step necessary to enable characterisation of the intrinsic transport properties of this semiconductor, which will allow in turn the validation of transport models, and eventually a deeper understanding and thus optimisation of PCBM-based solar cells. The conversion efficiency of organic solar cells has seen a steady and significant improvement over the last few years, recently reaching values above 10%, but a deeper understanding is needed to achieve further improvement.
What	What is the specific thing that the student will do, and how does it fit inside the overall project? Within this project the student will familiarise with current crystal growth techniques and will have a chance to develop them with the aim of growing even larger crystals, over different substrates, and with different derivatives of C60 or of other OS. Emphasis will be placed on the transfer to or incorporation of the crystals within structures suitable for measurement of their transport properties (either in field-effect transistors (FETs) or time-of-flight configurations), and their eventual characterisation.
Special Knowlegde	Basic concepts of electromagnetism and solid-state physics. Attendance of the “Plastic and Molecular Electronics” course is also expected for students wishing to take up this project.
Supervisor	Prof. Franco Cacialli f.cacialli@ucl.ac.uk