Large area small-molecule thin films deposited by the doctor blade technique implemented with computer numerical control machine

Abstract

A systematic study of parameters allowing small-molecule thin film deposition over a large area by the doctor blade technique is reported. The solution concentration, deposition temperature, and speed coverage of the deposition technique were evaluated to determine these parameters' importance on the thickness and homogeneity of the film. The solution concentration was 5, 7.5, and 10 mg/ml; temperatures from 75 to 100 °C and speed coverage of 250, 500, and 750 mm/min were evaluated. The best conditions to achieve homogeneous and smooth films were a concentration of 10 mg/ml, a preheating temperature of 100 °C, and a speed coverage of 500 mm/min. The average thickness for small-molecule films is about 80–86 nm, and roughness is as low as 1.7 nm. The values were comparable to those measured in films deposited by the spin coating technique. It should be worth noting that film deposition was conducted with a lab-design and fabricated computer numerical control machine. The deposited films were used as an active layer in light-emitting devices with an active area of 1.25 cm2. Therefore, it is possible to achieve a homogeneous small-molecule film by varying the parameters of both the solution and the deposition technique.