David J. Crouch

Organic field effect transistors from ambient solution processed low molar mass semiconductor–insulator blends

The morphology and organic field effect transistor (OFET) properties of two component blends of semi-crystalline 6,13-bis(triisopropylsilylethinyl)pentacene (TIPS-pentacene) with selected amorphous and semi-crystalline side chain aromatic low permittivity insulating binders deposited at room temperature under vacuum from a good solvent are reported. When blended with an amorphous binder there is evidence from X-ray photoelectron spectroscopy (XPS) of a strong interaction between TIPS-pentacene and the binder in the solidified film giving rise to twisted TIPS-pentacene crystals containing dislocations. Due to this strong interaction we see no evidence of segregation of TIPS-pentacene towards the active interface and hence we observe a rapid fall off in saturated hole mobility at an active concentration less than 50 wt%. When blended with a crystalline binder there is no evidence from XPS of any interaction between TIPS-pentacene and the binder in the solidified film. We propose that when a semi-crystalline binder is used, which crystallizes more slowly from solution than TIPS-pentacene, we observe stratification of the active material to both interfaces and as a result retention of saturated hole mobility even down to 10 wt%. The potential applications of the approach are in the formulation of low-cost organic semiconductors whose solution and solid state properties can be fine-tuned by careful binder selection.

High performance, acene-based organic thin film transistors

1,4,8,11-Methyl-substituted 6,13-triethylsilylethynylpentacene shows extended pi-pi overlap when deposited from solution, yielding organic thin film transistors with high and reproducible hole mobility with negligible hysteresis.

The synthesis, X-ray structures and CVD studies of some group 11 complexes of iminobis(diisopropylphosphine selenides) and their use in the deposition of I/III/VI photovoltaic materials

Reaction of NH(PiPr2)2 with elemental selenium in concentrated solvent conditions enables large scale preparation and improved yields of NH(PSeiPr2)2 that may be deprotonated with sodium methoxide to give NaN(PSeiPr2)2. Treatment of the sodium salt with appropriate Group 11 metal salts in methanol yields a range of trinuclear complexes. The protic solvent conditions utilized facilitate the reduction of copper(II) salts resulting in the isolation of copper(I) complexes. These new Group 11 complexes have been characterised by 1H and 31P NMR and IR spectroscopy, APCI mass spectrometry, microanalysis and X-ray crystallography. Thermolytic decomposition of the copper(I) precursors in the presence of the indium precursor, In[(SePiPr2)2N]2Cl, has been carried in the solid state using AA-MOCVD to give copper indium diselenide solid state materials CuInSe2.

Deposition of CdSe thin films using a novel single-source precursor; [MeCd{(SePiPr2)2N}]2

The novel complex [MeCd{(SePiPr2)2N}]2 has been synthesised and its structure determined by X-ray single crystal methods. The compound is suitable for the deposition of cadmium selenide films by low pressure chemical vapour deposition.

Further evidence for spontaneous solid-state polymerisation reactions in 2,5-dibromothiophene derivatives

Three new, highly crystalline 2,5-dibromothiophene compounds polymerise on standing in the absence of solvent and catalyst; X-ray crystallography shows that the molecules are held in close proximity by several short intermolecular contacts, facilitating the coupling of monomers.

New synthetic routes for quantum dots

Various methods for the synthesis of quantum dots of compound semiconductors are discussed. Emphasis is placed on methods involving the decomposition of chalcogenide–containing precursors in tri–n–octylphosphine oxide. The use of simple coordination complexes can avoid the use of pyrophoric precursors. Approaches based on melts or the use of imino–bisdichalcogeno–diphosphinates are also discussed. These routes may be suitable for the production of large quantities of quantum dots.

Organomercury-based imino-bis(diisopropylphosphine chalcogenide) complexes: synthesis and characterisation of novel hybrid “single-source precursors” for mercury chalcogenide solid-state materials

The synthesis and characterisation of the mercury(II) complexes [RHg{(SePiPr2)2N}] [R = methyl (2a), ethyl (3a), thienyl (T) (4a), 2-selenyl (SL) (5a) and phenyl (6a)], prepared by the reaction of the sodium salt of NH(SePiPr2)2 (1a) with the appropriate alkyl/aryl mercury halide in methanol are reported. Results are compared and contrasted to the corresponding sulfur analogues [RHg{(SPiPr2)2N}] [R = T (4b), SL (5b) and Ph (6b)], and these new compounds have been evaluated, by thermogravimetric analysis and mass spectrometry as potential precursors and powder X-ray diffraction used to identify solid-state products. The solid-state structure of the symmetrical complex Hg[(SePiPr2)2N]27a, and di(2-selenyl)mercury, one of the symmetrisation products of [SLHg{(SePiPr2)2N}] 5a in solution, have been determined by single crystal X-ray crystallography.

Hexyl‐Substituted Oligoselenophenes with Central Tetrafluorophenylene Units: Synthesis, Characterisation and Application in Organic Field Effect Transistors

A series of selenophene oligomers incorporating conjugated fluorinated phenylene units have been synthesised as potential semiconductor materials for organic field-effect transistors (OFETs). X-ray crystallography shows that the molecules are held in close proximity by several short intermolecular contacts, making them ideal candidates for OFET applications.

Fabrication of thin films of bismuth selenide using novel single-source precursors by metal organic chemical vapor deposition

A metal-organic compound, Bi[(SePiPr2)2N]3 has been synthesized and used as a single-source precursor for the deposition of bismuth selenide thin films via low-pressure metal-organic chemical vapor deposition. Crystalline thin films of rhombohedral Bi2Se3 have been deposited on glass substrates. The films have been characterized by X-ray powder diffraction, scanning electron microscopy and energy dispersive analysis of X-rays.

Structural and solvatochromic studies of a series of tricyanoquinodimethane-based zwitterions

The synthesis and characterization of three new solvatochromic tricyanoquinodimethane zwitterionic systems is reported. (Z)-{β-[N-(1-Propyl)benzothiazolium-2-yl]-α-cyano-4-styryl}dicyanomethanide, C3H7(2)BT3CNQ, (Z)-{β-[N-(1-propyl)benzothiazolium-2-yl]-α-cyano-4-(2,3,5,6-tetrafluorostyryl)}dicyanomethanide, C3H7(2)BT3CNQF4, and (Z)-{β-[N-(1-butyl)benzoselenazolium-2-yl]-α-cyano-4-styryl}dicyanomethanide, C4H9(2)BS3CNQ, exhibit negative solvatochromism, consistent with a transition from an ionic ground state to a significantly less polar excited state. X-Ray crystallography measurements confirm the zwitterionic ground state of these novel T3CNQ-based chromophores. The solvatochromic properties of these compounds are compared to those of a series of related quinolinium/pyridinium adducts, and also with those of the Reichardt betaine dye.