Study On The Effect Of Thermal Annealing On The Performance Of Organic Optoelectronic Devices

Organic photoelectric devices have been widely studied by many researchers because of their impressive advantages such as simple material synthesis,easy preparation,environmental protection and easy to realize large size,capability of integrating on flexible substrates.For example,organic light-emitting devices(OLEDs)have become a huge-scale industry,with the intensive research on organic optoelectronic devices,OLEDs also show great potential in the field of lighting;Quantum-dot light-emitting diodes(QLEDs)have great relevance to organic devices in the preparation process and device physics.And the functional layers based on organic materials play a key role in structure and performance optimization of QLEDs;Organic photovoltaic devices(OPVs)with low cost and high efficiency have important research significance in this energy age;Organic photodetectors(OPDs)have good biocompatibility and advantages in developing low-cost civil and commercial detectors.In a word,the research of organic optoelectronic devices with low cost,low power consumption,high efficiency and high stability is the goal which is pursued by the researchers in this field.This thesis will be based on organic optoelectronic devices,and the effect of thermal annealing on the performance of the device will be emphatically explored.The internal physical mechanism is revealed from the organic film formation and the change of the organic functional layer interface.We considered the cross study of the new material system and the optimization design of the device structure,to improve the performance of organic optoelectronic devices.The main results of this thesis are followed:1.The study on thermal annealing was applied upon QLEDs that utilize colloidal quantum dots as emitters and organic molecules/polymers as transporting materials.The multi-layer structure of ITO/PEDOT:PSS/poly-TPD/QDs/Alq3/Li F/Al was designed(the molar ratio of blue: green: red quantum dots was 96:5:1).The confocal microscopy was used to analyze the crucial correlation between the optical properties of quantum-dot films and their supermolecular arrangement.After thermal annealing process,the space vacancies in the quantum dots light-emitting layer are filled and more uniform film was induced,which effectively suppressed the inefficient emission from the electron-transporting layer material Alq3.Therefore balance white emission with CIE coordinates of(0.39,0.45)and color rendering index(CRI)of 71.4was successfully obtained.2.The thermal annealing process was also applied on planar heterojunction OPVs(PHJ-OPVs)using Cu Me Pc as the electron donors.With thermal annealing at proper temperature,the absorption of the functional layer was enhanced extended to lower energy attributed to the crystallization of Cu Me Pc.In this cell,Cu Me Pc was used as the electron donor and C60 as the electron acceptor,Mo Ox and V2O5 as the anode buffer layer.In addition to the improved absorption,the hole mobility of crystalized Cu Me Pc was also improved.Meanwhile,the crystallization of Cu Me Pc expanded the contact area of the D/A interface and avoided the "isolating island effect" usually observed in the BHJ structures.Therefore,The performance of our PHJ-OPVs after thermal annealing treatment were not only better than that of the cell without thermal annealing,but also better than the ones adopted with BHJ structure.PCE of 3.35%,Jsc of 9.85 m A/cm2,Voc of 0.533 V,and FF of 63.8% were achieved in the optimized cell.Based on the thermally annealed PHJ-OPVs,the researches on OPDs for red light were carried out.In this work,Mo Ox was used to mix with m-MTDATA as the anode buffer layer to improve the glass transition temperature of m-MTDATA.Moreover,the mixed buffer layer increased the light transmittance of the material in the red light region,and in turn further enhancing the photocurrent of the device.The Cu Me Pc crystallization after thermal annealing reduced the defect,thus further reduced the dark current.Compared with the annealed red planar heterojunction OPD,the dark current decreased by 67%,photocurrent increased by126% and shading current ratio increased by 578%.3.Researches on organic electroluminescent devices.The researches on the effect of thermal annealing upon the performances of blue phosphorescent OLEDs(Ph OLEDs)were carried out on the devices with SFX2 PO as the host and FIrpic as the phosphorescent dye.SFX2 PO is an excellent host material for blue Ph OLEDs attributed to its high triplet level(T1)and excellent carrier mobility.Improved properties of blue PHOLED have been achieved by optimizing the device structure and thermal annealing.In the optimized device without any out-coupling enhancements,a current efficiency(CE)of 21.68 cd/A and a power efficiency(PE)of16.65 lm/W corresponding to an external quantum efficiency(EQE)of 12.34% were obtained.This device also showed stable emitting color with CIE coordination slightly shifting from(0.15,0.28)to(0.17,0.29)over the ranging luminance of10-5000 cd/m2.