Abstract
In this study, we introduce optimization of the annealing conditions for improvement of hardness and hole transporting properties of high-molecular weight poly [9, 9-dioctylfluorene-co-N-(4-(3-methylpropyl)) diphenylamine] (TFB) film used as a Hole Transport Layer (HTL) of Quantum-dot Light-emitting Diodes (QLEDs). As annealing temperatures were increased from 120 °C to 150 °C or more, no dissolving or intermixing phenomena at the interface between HTL and Quantum-Dot Emission Layer (QDs EML) was observed. However, when the annealing temperatures was increased from 150 °C to 210 °C, the intensity of the absorbance peaks as determined by Fourier Transform Infrared (FT-IR) measurement was found to relatively decrease, and hole transporting properties were found to decrease in the measurement of current density - voltage (CD - V) and capacitance - voltage (C - V) characteristics of Hole Only Devices (HODs) due to thermal damage. At the annealing temperature of 150 °C, the QLEDs device was optimized with TFB films having good hardness and best hole transporting properties for solution processed QLEDs.
Highlights
Poly[N-vinylcarbazole] (PVK)[16], TFB17 and Poly[triphenyldiamine][18], etc., were used as Hole Transport Layer (HTL), but there has been no accurate analysis of the annealing conditions of HTL in Quantum-dot Lightemitting Diodes (QLEDs)
In Optical Microscopy (OM) imaging performed with UV exposure and Focused Ion Beam Scanning Electron Microscope (FIB-SEM) analysis to observe sufficient annealing conditions to prevent dissolution of the TFB film, it has been shown that the thickness and quality of a TFB film with sufficient annealing temperature can be maintained without being dissolved by the QD EML
TFB films at each annealing temperature used for UV-vis analysis were spin-coated on glass substrates in the same conditions as those used for QLEDs fabrication; the thickness was about 30 nm
Summary
Poly[N-vinylcarbazole] (PVK)[16], TFB17 and Poly[triphenyldiamine] (poly-TPD)[18], etc., were used as HTL, but there has been no accurate analysis of the annealing conditions of HTL in QLEDs. TFB is widely used as an HTL of OLEDs and QLEDs because it has good hole mobility[17,19] and its HOMO level is located between those of Poly [3, 4‐ethylenedioxythiophene]: poly [styrene sulfonate] (PEDOT: PSS) and green QDs. In this study, the results of UV-vis and FT-IR analysis, which are commonly used for the analysis of organic materials, show that the molecular structure of TFB film was damaged at excessive annealing temperatures. In Optical Microscopy (OM) imaging performed with UV exposure and Focused Ion Beam Scanning Electron Microscope (FIB-SEM) analysis to observe sufficient annealing conditions to prevent dissolution of the TFB film, it has been shown that the thickness and quality of a TFB film with sufficient annealing temperature can be maintained without being dissolved by the QD EML. The current - voltage - luminance (IVL) characteristics of QLEDs fabricated by spin-coating showed the same tendency as the previous optical and electrical analysis results
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