Abstract
Here, we report the hole injection role of p-type conjugated polymer layer in phosphorescent organic light-emitting devices (OLEDs). Poly(3-hexylthiophene) (P3HT) nanolayers (thickness = ~1 nm thick), which were subjected to thermal annealing at 140 °C by varying annealing time, were inserted between indium tin oxide (ITO) anodes and hole transport layers (N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine, NPB). The 1 nm-thick P3HT layers showed very weak absorption in the visible light range of 500~650 nm. The device results disclosed that the presence of P3HT layers were just able to improve the charge injection of OLEDs leading to an enhanced luminance irrespective of thermal annealing condition. The highest luminance and efficiency were achieved for the OLEDs with the P3HT layers annealed at 140 °C for 10 min. Further annealing for 30 min resulted in turn-down of device performances. The emission color was almost unchanged by the presence of P3HT layers even though the color coordinates were marginally fluctuated according to the annealing time. The present result delivers the possibility to use p-type conjugated polymers (i.e., P3HT) as a hole injection layer in OLEDs.
Highlights
BartolomeoSince the first report on organic multilayer structures, organic light-emitting devices (OLEDs) have been extensively studied and successfully commercialized for various applications such as smart phones, smart watches, television sets, etc. [1–10]
Results showed that the performance of OLEDs was certainly improved by introducing the P3HT layers between anodes and hole transport layers
The luminance and efficiency of devices were significantly enhanced by thermal annealing at 140 ◦ C for
Summary
BartolomeoSince the first report on organic multilayer structures, organic light-emitting devices (OLEDs) have been extensively studied and successfully commercialized for various applications such as smart phones, smart watches, television sets, etc. [1–10]. Since the first report on organic multilayer structures, organic light-emitting devices (OLEDs) have been extensively studied and successfully commercialized for various applications such as smart phones, smart watches, television sets, etc. The successful commercialization of OLEDs can be ascribed to advances in organic semiconducting materials for both emission and charge transport layers [11–18]. Optimization of device structures including the thickness of organic multilayers have greatly improved the performance of OLEDs [19–22]. The recently commercialized OLED displays consist of organic small molecules and are fabricated using thermal evaporation processes in a vacuum [31–33]. Practical roll-to-roll processes, which are considered one of the most effective and competitive processes for organic devices compared to inorganic devices, cannot be utilized owing to such vacuum systems [37–40]. Extensive studies have been carried out for solution-processed OLEDs by employing ink-jet printing processes [41–43]
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