Fabrication of an x-ray detector based on molecular plastic electronics

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.