A solution-derived bismuth aluminum gallium tin oxide film constructed by a brush coating method for spontaneous liquid crystal alignment

We present a facile liquid crystal (LC) alignment method using brush hairs. This one-step brush coating method integrated film deposition and alignment layer treatment, which guarantees a high throughput. Bismuth aluminum gallium tin oxide (BiAlGaSnO) was used for the alignment layer, and a uniform and homogeneous LC alignment state was confirmed for a 280 °C cured brush coated film by polarized optical microscopy and pretilt angle analysis. X-ray photoelectron spectroscopy was used to verify the formation of the BiAlGaSnO layer on the glass substrate. Atomic force microscopy confirmed the oriented structure on the BiAlGaSnO surface induced by the shear stress of brush movement and active thermal oxidation via the curing process. This anisotropic surface derives the uniform LC alignment via geometric constraints under the boundary condition of the interface with the LCs. The BiAlGaSnO surface exhibited hydrophilicity with a nanocrystalline structure in contact angle and selected area diffraction analyses. The thermal stability of the BiAlGaSnO film to LC alignment was confirmed up to 150 °C from the annealing process. The good electro-optical performance of the BiAlGaSnO film was also verified by the fast switching characteristics. Based on the above results, the brush coating method is expected to be an effective strategy for next-generation LC applications.