Time-resolved and space-resolved studies of the electrical response to X-rays of organic semiconducting single crystals

In recent years, organic semiconductors (OSs) demonstrated a great potential for electronic and optoelectronic applications (OLEDs, OFETs, OPV, etc) [1,2], but up to now their use as ionizing radiations detectors have been little investigated. Recently, we reported on organic semiconducting single crystals (OSSCs) used as effective, robust and reliable direct X-ray detectors [3]. Devices manufactured with solution-grown OSSCs from two different molecules, 4-hydroxycyanobenzene (4HCB) and 1,8-naphthaleneimide (NTI), have been operated in air, under ambient light and at room temperature, showing well reproducible performances and a stable linear response, under different X-ray doses. Driving voltages as low as 50 V, in unoptimized devices, were sufficient to obtain linear responses. A notable radiation hardness and resistance to aging was also found. The role played by metal contacts on the detector response has been investigated, leading to the fabrication of fully organic, optically transparent devices, characterized by good performances. In a previous beamtime on SYRMEP [4], we operated a full characterization of the electrical response of the above mentioned OSSCs-based detectors irradiated with X-rays at different energies (10-30 keV) and doses, relevant for dosimetric and security applications. In this range a good linearity of the device at dose rates between 1 and 170 mGy/s was found (figure 1), with sensitivities up to 0.05 nC/mGy for energy around 15-17 keV, confirming the possibility to use OSSCs as a new family of direct organic detectors. In particular, the possibility to use precision slits for focusing the beam only between the contacts, aiming at investigating the influence of the metal/OSSC interface in the charge photogeneration process was investigated (figure 2).