High-precision charge carrier mobility measurement with transient electroluminescence by eliminating trapped charges

Abstract Transient electroluminescence (TrEL) is an important technique for the device physics study of organic light-emitting diodes (OLEDs), especially for the analysis of charge carrier mobilities. However, existing TrEL-based mobility measurements are susceptible to the internal trapped charges, as manifested by the appearance of a shoulder peak on the rising edge, which consequently leads to the overestimation of the mobility values. In this work, a method has been developed to suppress the impact of trapped charges, thereby facilitating precise mobility analysis with thinner devices. An off-voltage dependent de-trapping rate was used to explain the de-trapping dynamics and trap-induced rising edge emission. By using longer pulse periods and larger negative off-voltages, the de-trapping of the captured carriers is enhanced, leading to suppressed shoulder peaks and thereby obtaining accurate mobility values for Alq 3 (3–5 × 10 −5 cm 2 /Vs), Bepp 2 (1–3 × 10 −5 cm 2 /Vs), BeBq 2 (4–9 × 10 −5 cm 2 /Vs), Bphen (1–2 × 10 −4 cm 2 /Vs), TPBi (5–8 × 10 −6 cm 2 /Vs), and TmPyPB (6–8 × 10 −5 cm 2 /Vs). This work paves the way for conducting reliable low-cost yet high-precision mobility measurements with TrEL.