Structural and Electric-Optical Properties of Zinc Phthalocyanine Evaporated Thin Films: Temperature and Thickness Effects

Abstract

It is known that the molecular architecture plays a fundamental role in the electrical and optical properties of materials processed in the form of thin films. Here, zinc phthalocyanine (ZnPc) thin films were fabricated through the vacuum thermal evaporation technique (PVD, physical vapor deposition) up to 50 nm thickness with the objective of determining their molecular architecture and some electrical and optical properties. Structurally, the results showed a uniform growth of the films depending on how the evaporation is performed (step-by-step or straightforward). The uniform films present a molecular organization dominated by the ZnPc macrocycle ring forming almost 90°in relation to the substrate surface. These films are crystalline (R-form) and possess molecular aggregates in the form of dimers (or higher order of aggregates) and monomers. Such aggregates are seen at the nanometer scale; however, at the micrometer scale, the films are morphologically homogeneous. In relation to the optical properties, it was observed that these films, besides absorbing in the ultraviolet-visible region, present a photoluminescence when irradiated with the 785 nm laser line. In terms of electrical properties, it was determined an electrical conductivity of ca. 10 -10 S/m and a significant photoconducting activity. Finally, a dependence of the molecular organization, crystallinity, and optical properties on the film annealing (and thickness) was investigated, and the sensitivity of the ZnPc PVD films against gasoline vapor was tested as proof-of-principle.

Effect of annealing on the growth dynamics of ZnPc LB thin film and its surface morphology

“…1, 2 Among the metal organic molecules, the metal-phthalocyanine (MPc) molecules have gained large attention because of their high thermal and chemical stability, high intrinsic charge carrier mobility, the ambipolarity of the charge carrier transport, and high absorption coefficient of order of 10 5 cm −1 . 3 Hence they have been applied to wide varieties of fields such as optolelectronics and electronics devices, [4][5][6][7] namely organic light emitting diodes (OLEDS), 8 photovoltaic devices, 9 memory devices, 10 organic solar cells 11,12 and sensors. 13 Therefore it is necessary to have proper understanding of surface morphology and growth mechanism of MPc's compounds in thin films for their technical application.…”

Structural modifications of zinc phthalocyanine thin films for organic photovoltaic applications

“…In most of literatures, phthalocynine films were prepared on clean substrates such as the single-crystal substrate and glass. [16][17][18] However, for OPV applications, the indium-tin-oxide (ITO) coated glass which has significant structural defects is usually used as a substrate. Understanding the growth of organic thin films on the ITO surface is becoming crucial for further improving OPV cells.…”

The molecular structure ordering and orientation of the metallophthalocyanine CoPc, ZnPc, CuPc, and MgPc thin layers deposited on silicon substrate, as studied by micro-Raman spectroscopy

“…Due to these exceptional properties, thin films of MPcs have been recently intensively investigated using the optical methods such as absorption ellipsometry, FTIR absorption, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and atomic force microscopy [11][12][13][14][15][16]. The preferred orientation is usually determined by sample preparation conditions such as the type of substrate (amorphous or single crystalline), type of deposited layer (different organic materials), temperature of substrate, deposition rate, quality of the substrate surface, and method of deposition.…”