Morphology and transport characterization of solution-processed rubrene thin films on polymer-modified substrates

Abstract

In this report, the morpho-structural peculiarities and the crystallization mechanisms in solutionprocessed, solvent vapor annealed (SVA) thin films of rubrene (5,6,11,12-tetraphenylnaphthacene) on different substrates were investigated. The high-quality rubrene crystal films with a triclinic crystal structure were successfully prepared on the FTO substrates (glass slide coated with fluorine-tin-oxide) modified by PLA (polylactic acid) for the first time. The area coverage of rubrene crystal and the sizes of rubrene dendritic crystals increased with increasing thickness of PLA film and concentration of rubrene solution. For rubrene molecules, FTO wafers with rough surface provided the possibility of heterogeneous nucleation. During the SVA process, there were two kinds of forces acting on the diffusion of rubrene molecules: one force was provided by the residual chloroform solvent, which was perpendicular to the substrate, and the other force was provided by gaseous dichloromethane, which was parallel to the substrate. The synergy of these two forces was proposed to explain the nucleation and the crystallization processes of rubrene films. The higher nucleus of PLA/rubrene dendrites and the layer-by-layer stacking of needle-shaped nanocrystalline PLA/rubrene were important for exploring their kinetic formation process. Organic semiconductor materials, due to their outstanding performance in electronics and optoelectronics, have become the global focus for their promising potential in the research and applications of thin films and flexible electronic device 1-3. Rubrene (5,6,11,12-tetraphenylnaphthacene), as a typical p-type organic semiconductor material, holds a very high record of field-effect mobility (20 cm 2 /V s) 4 in the form of orthorhombic single crystal grown by physical vapor deposition method (PVD) 5-7 , and therefore is used in organic field-effect transistors (OFETs) 8. Besides, rubrene single crystals can also be prepared by "hot wall" deposition method 9 , in situ vacuum annealing 10 , or solution growth methods (such as slow evaporation 11 and cooling from supersaturated solution 12). Rubrene thin films have been deposited by various techniques such as sol-gel coating 13 , combinatorial molecular beam epitaxy (MBE) technology 14 , solution-mediated vacuum deposition 15 , or spincoating 16. In initial works, OFETs based on rubrene thin-film demonstrated a very low mobility (~ 10-6 cm 2 /V s). 17 Then, the mobility of polycrystalline rubrene OFET with hexamethyldisilazane (HMDS) coated SiO 2 dielectric was found to reach up to 10-2 cm 2 /V s 18. For the crystalline rubrene, considered as the active channel in OFETs, a variety of insulating organic polymers and small molecules have been used to induce crystallization of rubrene. Among these, the popular organics were 5, 12-diphenylanthracene and (ultra)high-molecularweight polystyrene (UHMW-PS) 19 , poly(4-vinylpyridine) (P4VP) and poly(methyl methacrylate) (PMMA) 20 , 6,13-pentacenequinone (PQ) 21 , 6,13-diazapentacene (DAP) 22 and so on. In addit...

Perovskite-Sensitized Upconversion under Operando Conditions

“…To investigate the differences in film morphology, optical microscopy images of the UC device and the OSC-only film before and after being exposed to elevated temperatures were taken (Figures b and S8). Prior to heating, the expected continuous, smooth surface with no noticeable features is observed for both the UC device and the OSC film due to the amorphous nature of spin-coated rubrene thin films . Following heating, both regions with and without morphological changes are found; in particular, additional regions with a clear formation of crystalline OSC dendrites are observed.…”

“…Prior to heating, the expected continuous, smooth surface with no noticeable features is observed for both the UC device and the OSC film due to the amorphous nature of spin-coated rubrene thin films. 80 Following heating, both regions with and without morphological changes are found; in particular, additional regions with a clear formation of crystalline OSC dendrites are observed.…”

Flexible and Transparent Polymer-Based Optical Humidity Sensor

“…A variety of materials can be used for deposition on flexible substrates [3][4][5][6] but the ones that stands out due to easy deposition in the form of thin films, relatively low cost, tailored functionality and fast response are polymers [7]. A number of different polymers, suitable for use as flexible substrates for sensor applications, are reported in the literature, including polyethylene naphthalate (PEN) [8,9], polyethylene terephthalate (PET) [10][11][12][13][14], polydimethylsiloxane PDMS [15,16], polyimide PI [17][18][19][20], polyvinyl alcohol (PVA) [21][22][23][24], polylactide (PLA) [25,26], polyurethane (PU) [27,28], polysulfone (PSU) [29], polyetheretherketone (PEEK) [30,31] and polycarbonate (PC) [32], along with other materials such as common paper [33,34], flexible glass [35] and last, but not least, composite [36] and multilayer substrates [37]. Among the most commonly used flexible substrates, PI provides a great solution for devices with higher annealing temperatures; however, its amber color makes it unsuitable for devices that require transparency.…”