Abstract
Semiconductor films of organic, doped dimetallophthalocyanine M2Pcs (M = Li, Na) on different substrates were prepared by synthesis and vacuum evaporation. Tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) were used as dopants and the structure and morphology of the semiconductor films were studied using IR spectroscopy, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS). The absorption spectra recorded in the ultraviolet-visible region for the deposited films showed the Q and Soret bands related to the electronic π-π* transitions in M2Pc molecules. Optical characterization of the films indicates electronic transitions characteristic of amorphous thin films with optical bandgaps between 1.2 and 2.4 eV. Finally, glass/ITO/doped M2Pc/Ag thin-film devices were produced and their electrical behavior was evaluated by using the four-tip collinear method. The devices manufactured from Na2Pc have a small rectifying effect, regardless of the organic dopant used, while the device manufactured from Li2Pc-TCNQ presents ohmic-like behavior at low voltages, with an insulating threshold around 19 V. Parameters such as the hole mobility (μ), the concentration of thermally-generated holes (p0), the concentration of traps per unit of energy (P0) and the total trap concentration (Nt(e)) were also determined for the Li2Pc-TTF device.
Highlights
LiPc occurs in the χ and α polymorphs, depending on the synthesis route used for powder growth or on the substrate temperature used in thin-film deposition [11]
We examined the effect of deposition conditions on thin films and made a morphological characterization by Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS), whereas film structural evolution was monitored by IR spectroscopy and X-ray diffraction (XRD)
Organic M2Pcs (M = Li, Na) semiconductors using TTF and TCNQ as dopants were prepared. Thin films of these semiconductors were deposited by high vacuum thermal evaporation, which is an adequate technique to prepare thin films of high purity and to manufacture heterojunction devices without chemical decomposition of the organic semiconductors that compose them
Summary
The use of organic chemistry gives us new ways of modifying materials’ functional properties, opening several possibilities for inexpensive device manufacturing [1] The introduction of these materials permits the development of new, cheaper, optoelectronic devices, such as organic diodes [2], organic light-emitting field-effect transistors [3] and organic light-emitting diodes [4]. One of the objectives of this work was to develop four devices through the synthesis and analysis of the structure and to evaluate the optoelectronic properties of doped alkali M2Pcs, using disodium and dilithium in order to determine their employability as organic semiconductors. This work includes the analysis of the effect of alkaline atoms on the macrocycle center, and discusses whether the presence of two central atoms extends the conduction channels for charge transport
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