Abstract
AbstractLiquid crystalline materials possess great potential as emitters in organic light‐emitting diodes (OLEDs) due to their self‐assembling property, which may lead to anisotropic films and improved charge transport. Here, the key photophysical properties of the columnar liquid crystalline emitter perylene‐3,4,9,10‐tetracarboxylic tetraethyl ester (PTCTE) are investigated and the material is implemented into OLEDs. It is found that vacuum‐deposited PTCTE films exhibit preferential horizontal orientation of the transition dipole moment. Embedding the emitter into different host materials leads to increased photoluminescence quantum yield but reduces molecular orientation compared to the neat film. OLEDs containing PTCTE doped into an exciplex‐forming co‐host achieve very high luminance exceeding 10 000 cd m−2 at 5.7 V, which is among the best performances of OLEDs based on columnar liquid crystalline emitters reported so far.
Highlights
Organic semiconducting materials have may lead to anisotropic films and improved charge transport
We present several different organic lightemitting diodes (OLEDs) device structures that are based on the Discotic liquid crystals (DLC) emitter perylene-3,4,9,10tetracarboxylic tetraethyl ester (PTCTE) (Figure 1a)
In order to assess the potential of PTCTE as emitter material for OLEDs, we first investigated absorbance, photoluminescence (PL)
Summary
In order to assess the potential of PTCTE as emitter material for OLEDs, we first investigated absorbance, photoluminescence (PL). We incorporated PTCTE as neat emission layer (EML) and electron transport layer (ETL) into simple bi-layer OLEDs using either 2,2′,7,7′-tetrakis(N,N′-di-p-methylphenylamino)9,9′-spirobifluorene (Spiro-TTB) or N,N′-di(naphtalene-1-yl)N,N′-diphenylbenzidine (NPB) as hole transport layer (HTL) and LiF/Al as cathode (Figure 2a). This structure served as a reference to compare to literature devices using similar. Upon annealing of the device to 120 °C, we observed an increase in charge transport, especially at lower voltages This may be due to enhanced structural order at the interface between ITO and Spiro-TTB, which led to improved hole injection. The electroluminescence (EL) spectra of the OLEDs peak at 610 nm, indicating that emission originates predominantly from excimers (Figure S2c, Supporting Information).[22,37] The spectra are nearly independent of HTL material and PTCTE thickness, suggesting that optical effects play only a minor role
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