Solid-solution Deep-blue Crystalline Organic Light-Emitting Diodes With High Performance

The rapid development of the electronic information industry has promoted the progress of human civilization,and organic light-emitting diode(OLED)is one of the important display and lighting technologies.For full-color displays,blue light,especially deep-blue OLEDs,is crucial.High-performance deep-blue devices require not only high luminous efficiency but also high brightness at low driving voltage.Compared to traditional amorphous material systems,crystalline organic semiconductors(COSs)have highly ordered molecular arrangements,with high charge carrier mobility in terms of electrical properties and highly oriented molecular emission dipoles in terms of optical properties.Hence COSs are an ideal medium for producing OLED devices.This paper takes high-performance deep-blue OLED(C-OLED)devices as the research target and proposes a new route that combines weak epitaxial growth(WEG)and organic solid solution(OSS).This route can incorporate the properties of host and guest molecules into C-OLED devices through synergy and has been expanded and optically simulated and analyzed in the system.Then the system is expanded,and optical simulation analysis is carried out.This thesis is based on phenanthroimidazole materials 2FPPICz,BPPI and p-DPPI.The content is as follows:1.An innovative method has been developed to construct deep-blue C-OLED devices using crystalline organic solid solution(OSS)thin films.The 2FPPICz host molecules in the crystalline OSS thin films are almost parallel to the substrate,meanwhile,BPPI guest molecules can achieve horizontal-orientation transition dipole moment vector(TDMV)via the induced orientation from the host molecules.At a guest concentration of 6%,the proportion Θ of horizontal orientation is 92.5%.The 2FPPICz:6%BPPI C-OLED device achieved a maximum EQE of 6.5%for deep-blue,fluorescent C-OLED devices,and its CIE chromaticity coordinate was(0.15,0.07).Compared with amorphous OLED(A-OLED)devices reported currently with highEQE deep-blue light emission(CIEy≤0.08),this OSS-based C-OLED device has overwhelming advantages in terms of driving voltage(4.0 V@1000 cd/m2),power efficiency(3.9 lm/W@1000 cd/m2),series resistance Joule-heating loss ratio(11.1%@1000 cd/m2),and photon output capability,etc.In addition,crystalline OSS thin-film structure and morphology stability under high temperature and humidity environments also show significant advantages.These results undoubtedly prove the feasibility of a high-performance OLED crystalline route and demonstrate the superiority and synergy of OSS thin films in creating next-generation OLEDs.2.The OSS route is a new advantageous strategy for constructing C-OLED devices,so it is necessary to demonstrate its universality and expand its material system.We report a new crystalline OSS system by combining the 2FPPICz crystal host thin films with high-PLQY p-DPPI guest molecules,which can be used as EML in deep-blue,fluorescent C-OLED devices.In the 2FPPICz:6%p-DPPI crystalline OSS thin film,the p-DPPI guest molecules adopt a horizontally oriented molecular arrangement and the ratio Θ of TDM V orientation was 90%with respect to the substrate.In addition,the crystalline OSS strategy can produce high-PLQY luminescence(72%)integrated with an appropriate concentration of p-DPPI guest molecules,which significantly enhances PLQY compared to the 2FPPICz crystalline host thin film(29%).With these advantages,this OSS fluorescent C-OLED exhibits a deep-blue light emission with CIE chromaticity coordinates of(0.15,0.07),and has a maximum EQE of 5.3%,which significantly improves device performance compared to single-component C-OLED devices made from either 2FPPICz or p-DPPI alone.Moreover,due to higher conductivity,compared to traditional amorphous OLEDs with deep-blue light(CIEy≤0.08)reported previously,the OSS C-OLED has smaller ΔV of 1.6 V,and emitted larger photons under the same voltage,while series resistance Joule-heating loss ratio accounts for lower proportion(12.6%@1000 cd m-2).Therefore,these results further strengthen the feasibility of using crystalline OSS films for developing next-generation OLEDs.3.From the perspective of theoretical analysis,optical simulations were performed on the light loss modes of the above-constructed 2FPPICz:6%BPPI organic solidsolution C-OLED device.Through theoretical calculations.it can be determined that the corresponding optical outcoupling efficiency under horizontal orientation ratios of 0%.66.7%,92.5%.and 100%are respectively 0.2%,22.4%,33.2%and 36.6%.These results are consistent with the research analysis conducted in previous chapters,clarifying the importance of horizontal TDMV for OLED device efficiency.Through relevant analysis of electron transport layer(ETL)thickness,its optimal ETL thickness is found to be 44 nm,which is consistent with actual devices in Chapter 2.Based on this calculation results,an n-type doped BmPyPB:Li2CO3 was used as ETL to construct a 2FPPICz:6%BPPI solid-solution C-OLED device with a maximum EQE of 6%.It can also achieve high luminance at a low driving voltage(3.6 V@1000 cd m-2),as well as low series resistance Joule heating loss ratio(8.3%@1000 cd m-2).