Thin films of copper phthalocyanine deposited by solution processing methods

Abstract

In this work, we show and discuss the surface structure picture of copper phthalocyanine (CuPc) thin films deposited from trifluoroacetic acid (TFA) solvent onto silicon substrates at ambient conditions by four solution processing methods, namely drop-casting, dip-coating, spin-casting and spray-coating. The CuPc films were studied by AFM, as the main technique, and complemented by micro-Raman spectroscopy. Essentially, such thin films consist of CuPc molecular nanoribbons of a fixed ~1 nm thickness. CuPc molecules are arranged in an in-plane direction and formed in stacks under a defined tilt angle with respect to the substrate surface (monolayer) or underlying CuPc layer (multilayer). The film morphology takes various forms depending on the solution concentration, number of layers, and the deposition method. For instance, the morphology varies from very wide (~600 nm) but flat (~1 nm) ribbons for films prepared by dip-coating to crystallized rod-like features (multi-layered ribbons) when obtained by spray-coating. The factors studied in this paper should be taken into consideration in designing and controlling the criteria for rigorous CuPc film architecture.

Metal phthalocyanines: thin-film formation, microstructure, and physical properties

“…The specic fabrication parameters used for spray coating and spin coating in this case allows for sufficient TFA evaporation to create lms of large rodlike CuPc aggregates. 79 This further corroborates the relationship between thin-lm microstructure and solvent evaporation as the driving force for the nucleation and growth of solution deposited thin-lms.…”

“…9i, c). 79 Spray coated lms displayed a similar morphology and comparable surface roughness, coverage, and lm volume to spin coated lms with large rod-like CuPc aggregates (Fig. 9i, d).…”

“…9ii). 79 Dip coating yielded similar lm characteristics (roughness, coverage and lm volume) to drop casted lms, however exhibited a unique morphology consisting of a sub-monolayer mesh-like lm made of long, asymmetrically curved and interconnected nanoribbons approximately 600 nm wide where the CuPc molecules were orientated in-plane to the substrate (Fig. 9i, c).…”

“…[79][80][81] As the concentration of CuPc in the deposited solution increases, multiplayer formation is observed, however complete coverage for a single layer is never achieved due to the anisotropic nature of CuPc which effects surface diffusion and subsequent nucleation. [79][80][81] Solvent choice plays an important role in the formation of thin-lms by solution deposition. As discussed, the rate of solvent evaporation directly determines the crystallization rate, dictating the nal thin-lm morphology and microstructure.…”

“…8 ). 79–81 As the concentration of CuPc in the deposited solution increases, multiplayer formation is observed, however complete coverage for a single layer is never achieved due to the anisotropic nature of CuPc which effects surface diffusion and subsequent nucleation. 79–81 …”