On the way to the development of solar energetics, a big challenge is to provide the necessary protection and decrease weight of the solar panels. Films obtained from silicon-containing polymer precursors have become a promising encapsulation material due to their unique properties, such as high thermal stability, low water and oxygen transmission rates, good adhesion to various substrates, and high transparency in the visible range. The introduction of a carbon nanotubes (CNTs) into such a film could improve its mechanical properties, since CNTs can serve as a kind of reinforcement material.
In this work, composite glass-like thin films were obtained and their morphological features were studied. A film similar in composition to SiO2 with a small residual amount of N, obtained by curing of the preceramic polymer perhydropolysilazane (PHPS), was used as a matrix. Thin sheets of single-walled (SW) CNTs were used as a filler. The uniqueness of these composites lies in the fact that the CNTs are horizontally oriented inside the PHPS matrix, which suggests the anisotropy of some properties. For that one-layer thin films were spin-coated from 20% PHPS solution in dibutyl ether (durXtreme GmbH) onto the soda lime glass/Mo substrates, then dried onto hotplate (40 °C, 2 min) and cured by exposure to moderate temperatures (180 °C, 60 min) or using UV light treatment (40 min, 185 nm+254 nm wavelengths). SWCNTs were obtained by chemical vapor deposition during the decomposition of ferrocene vapor in a CO atmosphere. Films were formed at the outlet of the reactor by collecting tubes on filter paper. In this work, we studied the morphology of composite films with different architectures, as well as the influence of CNTs on the final properties of the composite film. The CNTs film was transferred either before the deposition of the PHPS layer or immediately after its deposition and drying, so the tubes were arbitrarily under or above the PHPS.
The transmittance (T%) of a pure SWCNTs film is 87% at a wavelength of 550 nm. Cured PHPS films also have a T% of about 90% in the visible range. The FTIR spectroscopy of composites showed that CNTs do not contribute to the spectra of cured PHPS films, which indicates relatively low concentration of SWCNTs in the samples. This is confirmed by the results of SEM with EDX analysis. SEM micrographs showed the formation of composite films with a thickness of 350-700 nm. The CNTs film, when it enters the PHPS matrix, remains densely packed and its thickness inside the composite is approximately 120 nm, as it can be seen from the cross-section SEM micrographs of the composite layers.
Thus, composite films of SiOxNy with horizontally oriented SWCNTs were prepared and characterized for the first time. Further search for new approaches to controlling the orientation of CNTs inside a polysilazane matrix will make it possible to obtain a number of composites with unique properties.