Organic-inorganic hybrid perovskites have been widely investigated for application in light-emitting devices (LEDs) due to their adjustable optical bandgap by changing the composition of the halide anions. Moreover, perovskites can be easily fabricated by solution process, which enables low-cost and large-area application. However, the perovskite materials are easily crystallized at low temperature, resulting in poor surface coverage with large-sized crystals. These non-uniform perovskite films induce high leakage current and poor contact with the adjacent layers. In addition, large-sized crystals effectively diffuse the generated excitons, which reduce the recombination probability. Thus, smaller-sized crystals are favored to limit the diffusion length of excitons or charge carriers and limit the dissociation of excitons into charge carriers. Therefore, producing uniform perovskite films with minimized grain size is an essential factor to achieve high performance perovskite LEDs (PeLEDs).
In this report, to improve the quality of perovskite films, a methylammonium lead bromide (MAPbBr3)-polymer composite film was fabricated by using a gas-assisted crystallization (GAC) method. N2 gas blowing during spin-coating process induced ultra-fast removal of the solvent, resulting in a high degree of supersaturation and a formation of a large number of nuclei, which promoted the growth of nano-sized grains. The optimized MAPbBr3-polymer composite film deposited by GAC method showed a uniform surface coverage with a grain size, thickness, and root mean square roughness of 79.3 nm, 509.4 nm, and 31.7 nm, respectively. A maximum luminance of 6800 cd/m2 and a maximum current efficiency of 1.12 cd/A were measured from the PeLED with MAPbBr3-polymer composite film deposited by GAC method. Finally, the same device with 1 cm2-area pixel exhibited a strong homogenous green emission centered at 528 nm. Therefore, it is believed that a uniform MAPbBr3-polymer composite film deposited by GAC method can satisfy high performance and large area application in perovskite-based optoelectronic devices.