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)
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.
Interface formation between organic semiconductors and substrates or electrodes is of great interest to develop functional
devices. In this paper we discuss on the interface formation between the organic semiconductor pentacene and silver as
the top electrode. Pentacene is commonly used as active layer in organic field-effect transistors (OFETs). It is known that
in OFEts significant percentage of the drain current is realized at organic layer thickness below 5 nm. Therefore,
understanding the monolayer regime is vital to identify the physics and chemistry of the organic semiconductor.
We report Raman spectroscopy measurements of 1.5 nm pentacene films deposited under high vacuum conditions onto
Au or SiO2 and covered by silver contacts. In order to achieve a detailed molecular identity upon metal evaporation,
Raman spectra at each evaporation stage was recorded. Analysis proved that a bare 1.5 nm pentacene film on smooth Au
substrates reflects significant enhancement of the Raman signal.
Silver contact of about 1 nm thickness promotes enhancement of the Raman internal vibrational modes along the
activation of normally infrared-active modes, and the enhancement factors are estimated to be close to 100. The Raman
spectroscopy measurements indicate absence of metallorganic pentacene-Ag complexes regardless of the substrate.