We demonstrated an area emission transistor with [Ir(ppy)₂pyim]PF₆/PMMA as the dielectric layer. The brightness can be tuned by V_DS and V_GS, respectively. The device performance was optimized by adjusting the mass concentration ratios of PMMA. Different working mechanisms of the devices with and without PMMA were investigated through the Kelvin probe force microscope. The doping of PMMA will change the surface potential of [Ir(ppy)₂pyim]PF₆, and then change the properties of charge injection. Our research may open up a new way for the development of multifunctional devices.