Detailed studies on energy loss mechanism in phosphor-sensitized fluorescent polymer light-emitting devices

Abstract

We studied the main energy loss mechanism in electroluminescent (EL) processes in phosphor-sensitized fluorescent polymer light-emitting devices. The used organometallic phosphor is fac-tris(2-phenyl-pridine) iridium [Ir(ppy)3] and the used red fluorescent dye is 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetrame-thyljulolidyl-9-enyl)-4H-pyran (DCJTB). The investigation found that due to the stronger electron trapping ability of DCJTB than that of Ir(ppy)3, the excitons prefer to form on DCJTB molecules. The charge trapping on the DCJTB molecules obviously restrain the function of the phosphor-sensitizer Ir(ppy)3. Moreover, the energy transfer from phosphorescent triplet state (Tp) to the fluorescent triplet state (Tf) also has great negative impact on the phosphor-sensitized fluorescent process. We clearly demonstrated these energy loss processes by steady-state and transient photoluminescence and comparison of device efficiency.