A Study Of Optoelectronic Properties Of F8BT Polymer Light Emitting Devices

Compared with traditional LCD displays,flat-panels based on organic light-emitting diodes?OLEDs?have many advantages such as low energy consumption,fast response,wide operating temperature range,self-illumination,etc.The development of advanced OLEDs is currently one of the research hotspots in the fields of display as well as solid-state lighting.OLEDs can be classified into two types according to the composition of the light-emitting layer:small molecule OLEDs and polymer OLEDs.Compared with small molecule OLEDs,polymer OLEDs have advantages in terms of stability,flexibility,and manufacturing cost.However,the performance of polymer OLEDs still can not meet the requirements of commercial applications and needs further improvement.In this thesis,Polymer OLEDs based on F8BT,a popular high-efficiency light-emitting polymer,were prepared,and their performance was improved by optimizing the device structure and post-annealing process parameters.The research has focused on the following three topics.?1?The structure of the F8BT OLEDs was optimized in three steps to study the effects of the hole transport layer,the electron transport layer and the light-emitting layer on the device performance.First,molybdenum trioxide?MoO₃?was used to replace the conventional hole transport material PEDOT:PSS in order to improve the thermal stability of the OLEDs.The thickness of the hole transport layer was further optimized to facilitate hole transport and achieve the best device performance.The current efficiency was increased to 2.7 cd/A at a driving current of 50 mA/cm² from 1.2cd/A for the OLED with a PEDOT:PSS hole transport layer.Next,three electron transport materials including TPBi,F8BT,and Bphen were compared in F8BT OLEDs.The luminance values of the three OLEDs were 1200 cd/m²,80 cd/m²,and 10 cd/m² at50 mA/cm²,respectively,confirming that TPBi is the optimal choice Finally,the spin coating speed and solution concentration of F8BT were varied to change the thickness of the light-emitting layer,and the impact on the device performance was studied.At 40mA/cm²,the OLED with a 50 nm F8BT emitting layer had the highest light-emitting power efficiency of 1.1.?2?The effects of annealing temperature on the luminous properties and lifetime of F8BT OLEDs were studied.F8BT films were prepared by spin coating,annealed at different temperatures,and characterized to investigate the effects of post annealing on the internal microstructure and surface morphology.The experimental results showed that when the films were annealed at 150^oC,the F8BT device had the maximum luminance of 1320cd/m² under the driving current of 50mA/cm²,and after annealing at300^oC,the F8BT OLEDs attained the maximum lifetime of 8.83 hours under constant current stressing at 20 mA/cm².?3?In order to suppress the short-wavelength secondary peak in the electroluminescence spectra,a BCP hole blocking layer was inserted at the interface of F8BT/TPBi.With a 15 nm BCP layer,the peak was completely suppressed.However,both the luminance and lifetime of the F8BT OLEDs were reduced by over 50%,suggesting that the BCP layer hampered charge transport and caused unbalanced charge injection.