Study On Red OLEDs Using Double-quantum-well Configuration And Top-emitting OLEDs On Silicon Substrate

Up to date, Flat Panel Displays (FPDs) are playing important roles formankind to get information and their effects are significant. Organiclight-emitting devices (OLEDs) are important members of FPDs andattract world wide attention in the fields of science and industry due totheir many merits of light weight, low cost, broad visual angle, highresponse speed, spontaneous light-emitting, high brightness and efficiency,etc. Since C. W. Tang and et al. report the high brightness OLEDs at lowoperating voltage for the first time in 1987, many progress have been made.By the use of novel materials, suitable structures and the efforts ofworld-known companies, OELDs are being moved out of the laboratoryand made into commodities. Although the performances of some OLEDsare high, further improving the performances of OLEDs is still the researchfocus in the world. So further to understanding the light emittingmechanisms of OLEDs and to designing reasonable devices structures areour research pivots in order to increase the performances of the devices.In this thesis, we have made some meaningful works relating to thedouble-quantum-well (DQW) OLEDs and the surface-emitting OLEDsusing on silicon substrate.1) In order to realize full color displays using OLEDs, the threeelemental colors of red, green and blue emitter with sufficiently highbrightness, efficiency and color purity are necessary. Although, among theRGB dopants, efficient green OLEDs have been demonstrated, red andblue emission, due to its low efficiency, would limit the development oforganic full color displays. To configuration of the device, quantum-wellstructure is an appropriate method to improve the performance of theorganic EL devices. However, multiple interfaces, due to its interfacedefects, may play some negative efforts on the performance of the organicmultiple-quantum-well (MQW) structure devices. Therefore, in this letter,we have fabricated the double-quantum-well OLEDs to improve a redemission. The structure of the device isITO/NPB(54nm)/DCJTB(2%):Alq3(4nm)/NPB(4nm)/DCJTB(2%):Alq3(4nm)/Alq3(34nm)/LiF(0.5nm)/Al, in which NPB is used as potentialbarriers and hole transport layer, DCJTB doped tris Alq3 as potential wellsand emitter, undoped Alq3 as electron transport layer, respectively. Theperformance of the DQW device is better than that of the heterostructuredevice. The turn-on voltage is about 4 v. The maximum brightness and ELefficiency of the device can reach 5916 cd m-2 at 16 v and 2.85 cd A-1 at 7 v,respectively. Moreover, the EL efficiency of the device is nearly relativelyindependent of the drive voltage in the range from 5 v to16 v, which isbeneficial to improve the longevity of the device. The better performanceof the DQW device is attributed to the confinement effect of quantum wellstructure.2) The conventional OLEDs structure consists of a multiplayerorganic stack sandwiched between a transparent conductive anode and anopaque metal/alloy cathode. Using this device architecture, the emittedlight is observed through the transparent ITO bottom electrode and theglass substrate. On the contrary to the conventional OLEDs, the emittedlight is coupled out through a semi-transparent top electrode in thetop-emitting OLEDs. Silicon wafer, on which the complicated driveelectronics and pixel switching elements can be integrated, may beemployed as the substrate in in the top-emitting OLEDs, which isdefinitely desirable for an active-matrix microdisplay. The electrodematerials and the carrier injection properties of the electrode are twocrucial factors for the performance of the top-emitting OLEDs. Copperphthalocyanine (CuPc) is analyzed widely as the buffer layer interposedbetween an ITO anode and a HTL. It has been demonstrated that theefficiency and stability of the OLEDs can be dramatically improved byusing the CuPc buffer layer. Therefore, in this letter, we have fabricated thetop-emitting OLEDs employing Au anode and LiF/Al/Ag cathode with theCuPc buffer layer on silicon substrate. The structure of the devices is Si /SiO2 /Au (60 nm) /CuPc (x nm) /NPB (50 nm) /Alq3) (50 nm) / LiF ( 0.9nm ) / Al (3 nm) / Ag (20 nm), in which x is 0 and10 nm, respectively. Theluminance of the device without CuPc is 0.49cd/m2 at 9 v, but theluminance of the device with 10nm thick CuPc is 9.31 cd/m2 at 7 v. Thisindicates that the CuPc buffer layer could lower the drive voltage. Thepeak luminances of the device with and without CuPc are 10080 cd/m2 and10210 cd/m2, respectively. This is a bette result in the top-emitting OLEDs.The peak efficiency (1.69 cd/A) of the device with 10nm thick CuPc isabout three times higher than that of the device without CuPc (0.61 cd/A).The effects of the CuPc buffer layer on the hole injection efficiency of thetop-emitting OLEDs using Au anode are obvious. Au, due to its high workfunction, low resistivity and insensitive to the oxygen and moisture, is a...