Brush-coating For Large Area OLED

Organic light-emitting diodes(OLEDs)provide a promising way for the development of future flat panel displays and solid-state lighting,due to their inherent characteristics such as low driving voltage,high brightness and efficiency,etc.Vacuum vapor deposition is nowadays the most widely used technique to prepare OLEDs.However,it usually sustains high cost,serious energy consumption,complex process,as well as waste of raw materials.Under this circumstance,solution process has been developed and aroused extensive attention,but the common solution process of spin coating still has disadvantages,such as low utilization rate of raw materials,incompatibility with large area and patterned preparation.Thus,it is imperative to develop new technologies to solve these problems.In this thesis,we established a new technology of brush coating to fabricate OLED devices,and systematically investigated the influence of brush coating process on film quality and device performances.It was observed that the as-fabricated devices demonstrated comprehensive performances comparable to that of the spin-coated devices,which suggests a feasible technique for future large-area high-performance OLED devices.The research content of this thesis is as follows:?-phase poly(9,9-dioctylfluorene)(PFO)films have been constructed in one step by direct brush-coating PFO solution onto substrates.The alignment of PFO chains was manipulated under directional stress,so that the coplanar orientation of adjacent fluorene units forms?-phase PFO.Both additional absorption peak and red-shifted photoluminescence(PL)spectra suggest the formation of?-phase for the brush-coated PFO films.?-Phase PFO device shows pure-blue emission with corresponding CIE coordinates of(0.170,0.112),achieving a high current efficiency of 3.37 cd/A,which is twice as efficient as the device with spin-coated amorphous-phase PFO films.In addition,the?-phase device shows much more stable EL spectra as compared with that of the amorphous-phase.The results suggest that brush-coating can be used as a simple and efficient methodology to orient the polymer semiconductor films for applications in constructing high-performance optoelectronic devices.To meet the demands of the commercialization of large-area devices,a new solution process is stringently needed.As a novel solution process for preparing film,brush coating technology shows various advantages,including large-area fabrication,high patterning ability and nearly 100%material utilization rate,which therefore holds great promise for large-area devices.Here,high efficiency phosphorescent WOLED was successfully prepared by continuously brush-coating the hole transport layer and the small molecule white light emitting layer.Under the optimized substrate temperatures and solution concentrations,high-quality smooth films was achieved and the subsequent devices exhibited a maximum luminance of 29200 cd/m~2 and current efficiency 29.3cd/A,which was comparable to that of the spin-coated devices.These results show that brush coating technology is a simple and effective method for preparing smooth films as well as large-area,flexible and patterned high-performance light-emitting devices.Considering the high stability and the excellent compatibility with the active matrix OLED panel,an inverted OLED was further constructed via continuously brush-coating the metal oxide electron injection layer,ultra-thin polymer modification and small molecule organic light-emitting layer.By regulating the solution concentration and the substrate temperature,high-quality films with ideal thickness was successfully obtained and the inverted phosphorescent white OLED based on these films demonstrated superior performances with the maximum brightness of 22778.9 cd/m~2and current efficiency of 20.7 cd/A.In short,high-performance light-emitting devices have been successfully prepared through systematic investigation and optimization of process parameters in brush coating,which provides reference for the efficient construction of low-cost,large-area and flexible light-emitting devices.