The Study Of Flexible Organic Light-Emitting Device (FOLED) By Employing The Substrate Transfer Method

Organic light-emitting diode (OLED) have lots of special advantages, such as lessweight, fast response speed, low energy consummation, broad operating temperature,more choices of materials, flexible display, etc. Thus, it is rather advantageous in thefields of display and lighting. Because of its good characteristics mentioned above,more and more people go into the research about OLED. In the thesis, a new methodis put forward to fabricate Flexible Organic light-emitting diode (FOLED). In otherwords, Flexible substrate with metal electrode is made by the substrate transfer intothe fabrication of FOLED. The flexible substrate is made through the substratetransfer. In the process, this technique requires a rigid basement, whose surface mustbe clean and smooth. The rigid basement mentioned in the discourse is washed by theliquid of acetone, ethanol, demonized respectively and meanwhile, it is dealt with bythe substratum of ultrasound glass. All these processes make it clean. A layer of Agwas deposited upon the substrate by the technology of vacuum thermal deposition.The substrate is used as electrode with a thickness of80nm. After that, NorlandOptical Adhesive63(NOA63) is spun on clean glass substrate with Ag. Duringspin-coating its speed and time need to be controlled. In this discourse, there were twoprocesses of spin-coating. The first period is200r/min and it lasts5s；The second,700r/min and20s.Then put the basement of glass in the UV light to cure NOA63afterspin-coating. The cured NOA63is similar to the PET which becomes flexible andhighly transparent thin film. Finally, NOA63and the rigid glass substrate are divided,after which it is realized that Ag electrode is transferred to the cured NOA63.Theelectrode in flexible substrate fabricated by the this method is quite smooth, which isconductive to the injection of carrier. We used atomic force microscope (AFM) towatch the two-dimension and three-dimension topography of Ag electrode in thesubstrate and the morphology of electrode in the flexible substrate by transfer technology to compare with the electrode morphology in the rigid glass substrate byvacuum thermal deposition. We can come to a conclusion that the electrode in theflexible substrate by transfer technology is more flat and smooth. From twoparameters of the highest peak and their roughness, the electrode in rigid glasssubstrate has the highest peak of4.6nm and its roughness of1.24nm; the electrode inflexible substrate by the substrate transfer features the highest peak of2.9nm and theroughness of0.719nm. The comparison in the two aspects further illustrates theadvantages of transfer technology. In addition, OLED is very sensitive to vapor andoxygen in the atmosphere. Therefore, black spots will appear on it or directly lead toits failure when the OLED is on in the air for a long time. This phenomenon resultsfrom organic materials in OLED， which occurs the chemical reaction with vapor andoxygen in the atmosphere. Thus, the problem of OLED encapsulation needs quicksalvation. First, we encapsulate the OLED with rigid Glass to prove the good functionof thin-film encapsulation. However, the thin-film encapsulation of FOLED can betterits value. Thus, there is an innovative point in this article is that a encapsulated layerof OLED in the process of substrate fabrication comes into being. The specificmethod is as following: A layer of Al2O3with a thickness of60nm is deposited byAtomic layer deposition (ALD) to isolate OLED from water steam and oxygen in theatmosphere after growth of Ag electrode in the glass, and then transfer theencapsulation layer together with Ag electrode, the encapsulation layer can adhere tothe substrate so that the OLED has realized a packaging, the packaging layer plays agood effect on OLED. And then transfer the encapsulation layer together with Agelectrode, the encapsulation layer can adhere to the substrate so that OLED ispackaged. And the packaging layer plays a good effect on OLED. This process needto use the technique of atomic layer deposition. The biggest drawback of ALD is thatis requires a long time in the process of fabricating encapsulation film. Due to thepackaging layer is completed before fabricating devices, so the whole process is not awaste of time. Therefore, not only the idea improves the efficiency of theencapsulation of OLED, but also it saves time and reduces the difficulty of theprocess. Encapsulation layer needs a test of its performance. This discourse applies calcium electrical test to macroscopic research and quantitative analysis of theperformance of Al2O3encapsulation layer formed by ALD. The reason why wechoose the method of calcium electrical testing is that calcium is a kind of metalsensitive to water steam and oxygen. Calcium will quickly become transparentcalcium hydroxide when contacting with water vapor and oxygen in the atmosphere.The time when calcium grows transparent will be extended if the thin film can stopwater vapor and oxygen. On the other hand, calcium is a kind of metal with goodelectrical conductivity when it does not come into conduct with water steam andoxygen. On the contrary, it will become calcium hydroxide non-conductive toelectricity when calcium reacts with steam and oxygen. Although the film has certaineffect on encapsulation of water vapor and oxygen, there is no absolute encapsulation.Therefore, calcium react with water vapor and oxygen in the atmosphere slowly, theresistance of calcium in the encapsulated layer also will slowly increase. The factorcan help to judge its quality.At last, we use the flexible substrate with a metal Ag electrode by technology ofsubstrate transfer to make a set of FOLED, The device:NOA63/Ag(80nm)/MoOx(5nm)/m-MTDATA(30nm)/NPB(20nm)/Alq3(50nm)/LiF(1nm)/Al(5nm)/Ag(15nm).The device of a flexible substrate compared with the deviceof rigid substrate, the structure of OLED with rigid substrate：Glass/Ag(80nm)/MoOx(5nm)/m-MTDATA(30nm)/NPB(20nm)/Alq3(50nm)/LiF(1nm)/Al(5nm)/Ag(15nm). A conclusion is reached after the comparison that flexibledevice does not own worse effects than the device with rigid substrate. This meansthat the flexible electrode made by the technique of substrate transfer has achieved abreakthrough and lays a certain foundation on the research of FOLED. The next stepfor us is that FOLED needs thin film encapsulation and tests its life-time. Delightfulachievements will come true.