High Efficiency Quantum Dots Light Emitting Diodes Via Film Morphology Control

This paper mainly focuses on improving the performance of quantum dots light emitting diodes(QLEDs)via film morphologies control,which plays crucial role on carrier injection,transporting and recombination in device.We fabricated high performance QLEDs by carefully controlling the film morphologies of hole transport layers(HTLs)and QDs layers.We analyzed photoelectric properties and film morphologies in detail by current density-voltage-luminance(J-V-L),atomic force microscopy(AFM),scanning electronic microscopy(SEM),transmittance electronic microscopy(TEM),fluorescence microscopy,ellipsometer,Fourier transform infrared spectroscopy(FTIR),contact angle,and UV-vis spectra measurements.Our work mainly consists of following two parts:In all solution processed QLEDs,in order to avoid the existed layer being destroyed by processing the upper layer,solvents for the adjacent layers should be orthogonal,which means that the solvent polarity difference should be large enough.However,there are still some situations where the orthogonal rule is hard to be satisfied.Herein,we demonstrated a photo-chemical cross-linking method to achieve solvent stable HTLs.QDs on the cross-linked HTLs exhibit better morphologies,leading to doubled EQE of the cross-linked HLTs based device.In addition,this photo-chemical strategy avoids any high temperature treatment,allowing us to fabricate high performance flexible devices on PET/ITO substrates.This method provides an effective way to fabricate high performance flexible device while suitable orthogonal solvents are hard to select in all solution processed photoelectrical devices.There are no detail investigations on how to select suitable solvents for QDs dispersion in all solution processed QLEDs.Here,we demonstrated the solvents and environment effects on final QDs film morphologies,revealing that the surface tension,vapor pressure,solubility of solvents and spin-coating methods and surrounding environment play crucial roles on film morphologies.QLEDs devices based on octane exhibit an EQE of 15.45%which is one of the highest value in similar devices.This method unveils the main effects on QDs film morphology,supplying a simple way to fabricate high performance QLEDs via all solution processed method.