Absorptive and conductive cavity cathode with silver nanoparticles for low-reflection organic light-emitting devices

We have successfully fabricated a low-reflection organic light-emitting diode (LR-OLED) by replacing the highly reflective Al cathode of a conventional OLED with a Fabry-Perot (FP) cavity cathode, which is simultaneously responsible for absorption, plasmonic absorption and destructive interference. The FP cavity cathode consisted of a front semi-transparent double thin metal layer (Al/Ag), an inserted organometallic black layer (BL) in the middle and a highly reflective Al mirror. The organometallic BL contained a high-mobility electron transport and broadband absorptive organic matrix, N,N'-bis(2,6-diisopropylphenyl)-1,7-bis(4-methoxy-phenyl) perylene-3,4,9,10-tetracarboxydiimide (MPPDI), and Ag-nanoparticle (NP) dopants which contributed not only to the plasmonic absorption but also to the metallic conductivity. By adjusting the thickness and Ag-NP concentration of the organometallic BL, one can optimize the destructive interference cavity effect. LR-OLEDs fabricated using the aforementioned characteristics of the Ag-NP yielded superior electrical performance and low reflection across almost the entire visible spectrum. With the exemption of surface reflection (air/glass ∼4%), a lowest reflection of 0% near 750 nm and an average reflection of 1.39% for the entire visible spectrum were obtained for a LR-OLED with a 65 nm organometallic BL (mixing ratio of MPPDI : Ag = 10 : 1). With the additional structural cavity cathode, the LR-OLEDs nonetheless exhibited similar electrical performances and continuous operational lifetimes to those of control devices with a traditional highly reflective Al cathode.