Contatto di riferimento: Laura Basiricò
Partecipanti: Dr. Andrea Ciavatti
Organic semiconductors are attracting a large interest as they allow to realize organic electronic and photonic devices spanning from field effect transistors, solar cells, light-emitting displays, smart tags and molecular sensors, that can be produced using large-area fabrication techniques, with advantages like low fabrication cost, low environmental impact and the possibility of creating transparent and flexible devices, allowing unprecedented and integrated device functions and architectures.
Organic materials have been so far mainly proposed as detectors for ionizing radiation in the indirect conversion approach, i.e. as scintillators, which convert ionizing radiation into visible photons, or as photodiodes, which detect visible photons coming from a scintillator and convert them into an electrical signal.
Meanwhile, traditional materials (Si, CZT, a-Se) for direct solid-state detection (i.e. X-ray photons are directly converted into an electric signal within the crystal) suffer from severe limitations for their mechanical stiffness and processing into large-area pixelated detector matrices in expensive growth facilities, thus the research interest on alternative materials for innovative ionizing radiation detection is rapidly growing. In this framework organic semiconductors are very promising candidates, and several attempts have been made in the last few years in the development of low-cost, low-power consuming, flexible and large-area organic direct detectors.
We studied and modeled the direct X-ray photo-conversion in micro-crystalline thin films of TIPSpentacene deposited by drop casting onto flexible PET substrates. We found that these devices are characterized by an unexpected high X-ray sensitivity that we justify by interpreting the detection mechanism as a photo-modulation of the semiconductor conductivity due to charge accumulation during X-ray exposure, resulting in a photoconductive gain effect.
From such findings, we develop a kinetic model that gives an important insight into the physical process that leads to highly sensitive response to ionizing radiation by such low-Z organic materials.