Effects of the emission layer structure on the electroluminescence performance of the white organic light emitting diodes based on thermally activated delayed fluorescence emitters

Abstract

White organic light emitting diodes (WOLED) employing blue, green and red thermally activated delayed fluorescence (TADF) emitters of DMAC-DPS(B), 4CzIPN(G) and 4CzTPN-Ph(R) and various emission layer (EML) structures of G/B, G/R/B and R:G(4CzTPN-Ph(R) doped in 4CzIPN(G) host)/B are fabricated and the effects of the EML structure, including EML thickness and 4CzTPN-Ph(R) dopant concentration, on the electroluminescence (EL) performance are investigated. It is found that the WOLED with the simple EML structure of G(20 nm)/B(10 nm) demonstrates maximum power efficiency (PE) around 16 lm/w and color rendering index (CRI) of 81. Meanwhile, R:G/B EML exhibits better EL performance than that of G/R/B EML. Especially, striking high CRI of 90 together with maximum PE around 13 lm/w can be obtained for R(1 wt%):G(20 nm)/B(10 nm) EML by meticulously modulation of EML thickness and 4CzTPN-Ph(R) dopant concentration, indicating the achievement of balance between EL efficiency and CRI for non-doped TADF emitter-based WOLED. Furthermore, the stacked EML of G(20 nm)/R(0.1 nm) and G(20 nm)/R(0.1 nm)/B(10 nm) reveal much more serious obstruction of delayed fluorescence (DF) compared to mixed EML of R(1 wt%):G(20 nm) and R(1 wt%):G(20 nm)/B(10 nm), implying more intensified quenching effects from the sandwiched 0.1 nm 4CzTPN-Ph(R) layer which will lead to deterioration of EL performance. Different energy transfer routes are derived based on the transient photoluminescence decaying dynamics of R(1 wt%):G(20 nm)/B(10 nm) and G(20 nm)/R(0.1 nm)/B(10 nm) EML and the sandwiched 4CzTPN-Ph(R) ultrathin layer is found to be critical. The decaying dynamics responsible for such EML structure dependent EL performance is discussed in detail.

Recent advances in thermally activated delayed fluorescence for white OLEDs applications

“…The strategy of all TADF is a novel mechanism to achieve high-efficient WOLEDs comparable to all-phosphorescent WOLEDs. The utilizing of TADF reduces the problem of the high production cost of phosphorescence and the degradation in the blue spectral region [36,95,96]. Therefore, all TADF-based WOLEDs can achieve high efficiency, small price, and stable color by adjusting the dopant concentration and the EML thickness reasonably.…”

Study on the exciton dynamic processes of exciplex host-guest system by transient magnetic field effects

“…configurations [1][2][3][4]. The first generation fluorescent materials can only utilize the singlet excitons, and the subsequent phosphorescence counterparts can harvest all the excitons by introducing internal heavy-metal effect [5][6][7].…”