Abstract
We present an organic X-ray detector with an active layer deposited from a novel semiconducting ink formulation. The precursor ink consists of blended poly(3-hexylthiophene-2,5-diyl) (P3HT), phenyl-C61-butyric acid methyl ester (PCBM) and the organometallic nanostructure copper(II) 2,2'-bipyridine (Cu(II)BPY).
The use of ligands like 2,2' byripidine with cationic species such as Cu(II) improves their solubility in organic solvents. The purpose of the organometallic complex Cu(II) BPY is twofold: to achieve a homogeneous semiconducting ink with P3HT: PCBM blends and to enhance the X-ray interaction with the organic layer through the Cu(II) cation.
Our X-ray displays consist of several pixels, each with vertical structures comprising a bendable PET/ITO substrate with a spin-coated semiconducting ink of P3HT: PCBM: Cu(II) BPY (60 nm), followed by thermal evaporation of Al (100 nm) contacts.
To the best of our knowledge, this is the first example where an organic X-ray detector includes the organometallic complex Cu(II) BPY in P3HT: PCBM blends, and the electrical characterization of the detector is carried out by impedance spectroscopy (IS).
In order to test the devices, each pixel is exposed to X-ray energies ranging from 0 keV to 35 keV and characterized by impedance spectroscopy (IS). Impedance spectra were recorded at frequencies between 20 Hz and 20 kHz and at a modulating signal of 50 mV. Analysis of IS measurements revealed a linear dependence between impedance and X-ray energy. IS analysis is more sensitive compared with standard photocurrent-voltage characteristics.