Effect of solvent polarity on the performance of thermally activated delayed fluorescence OLEDs

Molecular orientation in organic light-emitting diodes (OLEDs) is now regarded as an important factor that affects device efficiency. Herein, different polarity solvents were used to investigate the effect of solvent polarity on the molecular orientation and optoelectronic characteristic of spin-coated thermally activated delayed fluorescence (TADF) molecules. The lower solvent polarity is beneficial to enhance the photoluminescence (PL) intensity, photoluminescence quantum yield (PLQY) and the horizontal orientation of the emission molecule. And the higher horizontal orientation ratio promoted the carrier transport measured from the single carrier devices. The optimized performance of the OLEDs was obtained in the OLEDs based on the spin-coated emission layer with lower polarity solvent. The combined effect of PLQY, horizontal orientation ratio, surface morphology, and carrier mobility of the EMLs was ascribed to the enhancement of OLEDs. It indicates that optimizing the solvent polarity is an effective way to enhance the performance of solution processed OLEDs.