Research On White Organic Light-emitting Devices With Quantum Dot Down-conversion Films

In recent years,organic light-emitting devices(OLEDs)have received particular attention in the scientific community.And along with the development of OLEDs,they have entered the industrial stage in the fields of lighting and display.There are many new electronic products based on OLED technology on the market,such as smart phones and TVs.However,the conventional white OLEDs,especially top-emitting white OLEDs,have poor spectral stability,and the common manufacturing process of OLED displays is difficult and costly.These problems not only reduce the performance of OLEDs,but also become the barriers for the commercialization of OLEDs.In this paper,we adopt down-conversion structure to fabricate white OLEDs with relatively high spectral stability by combining quantum dot(QD)-based down-conversion films with blue OLEDs,and high-performance RGB OLEDs are prepared by using color filters,and their application in full-color display is discussed.First,we study the performance of bottom-emitting and top-emitting blue OLEDs,and produce high-efficiency blue OLEDs by optimizing the device structure.For the bottom-emitting blue OLEDs,we explore the effects of the thickness of electron transport layer and the light extraction layer with microstructure on device performance.For the top-emitting blue OLEDs,we investigate the influence of microcavity effect on device performance,by changing the length of the microcavity and the thickness of the light extraction layer.Then,CdSe/ZnS red QDs are used as the down-conversion material to prepare flat down-conversion films with different concentrations,and these films are combined with blue OLEDs to fabricate white devices,and we can control the spectra through varying the concentration of QDs in the down-conversion film.In addition,we prepare the patterned down-conversion film with microcylinder arrays by transfer printing,and it is combined with different blue OLEDs to produce bottom-emitting and top-emitting white devices with the maximum current efficiency of 19.1 and 20.6 cd/A,respectively.Moreover,the white devices based on the down-conversion system have excelent spectral stability,and the spectra and color coordinates are nearly invariable under different voltages.And with the comparison between the devices using flat down-conversion film and patterned down-conversion film,we explore the principle of using microstructure to improving the light extraction efficiency and angular characteristics of the devices.The results indicate that,after introducing the microstructure on the surface of the down-conversion film,the power efficiency and external quantum efficiency of the white device are significantly enhanced,and the angular distribution and angle stability of the top-emitting device are improved.Finally,green QD-based down-conversion film with microcylinder arrays is fabricated by using CdSe/ZnS green QDs as down-conversion material.The patterned red down-conversion film,patterned green down-conversion film and color filters are combined with the bottom-emitting and top-emitting blue OLEDs to fabricate the RGB devices,respectively.The color coordinates of the bottom-emitting RGB devices are(0.70,0.30),(0.28,0.64)and(0.10,0.16),and the color coordinates of the top-emitting RGB devices are(0.70,0.30),(0.24,0.62)and(0.10,0.20),respectively.The color gamuts of display devices based on these bottom-emitting and top-emitting RGB devices reach up to 83.1% NTSC and 75.2% NTSC,respectively.