Organic small molecules semiconductors as direct X-ray detectors

Organic small molecules semiconductors are promising in the field of direct ionizing radiation detection. Unlike their inorganic counterpart, these molecules are easy to work with, since they are flexible, soluble and can be deposited on electronic devices with very simple processes, such as drop-casting and spin-casting. Moreover, these materials have good detection properties and very low working voltage. To this day, organic semiconductors have mainly been used in indirect radiation detection, employed both in scintillator and as photodetectors. However, direct detection of ionizing radiation is a far more effective method, since it is performed within a single material and a single conversion, directly from photons to electrical signal; furthermore, it provides a higher signal-to-noise ratio and a faster response time. In this experimental work, I fabricated four direct detectors based on transistors; two different organic solutions were drop-casted onto the transistors, creating a conduction channel between source and drain electrodes. Both these solutions had chlorobenzene as a solvent, with DiF-TES-ADT and DiF-TEG-ADT as solutes, respectively, in a 0.5% concentration. The purpose of this thesis is dual. Firstly, I want to study how the detectors’ sensitivity is influenced by semiconductor molecules with different Z-number; secondly, I want to test a new drop-casting method (SAC method) and compare it to results previously obtained with traditional deposition methods. The results are very promising, with very high values of sensitivity obtained with low voltages.