Design And Fabrication Of Single-layer OLEDs

Recently, single-layer organic light-emitting devices (SLOLEDs) have been theresearch hot spots due to its’ relatively more simple device structure and easierfabrication process. In SLOLEDs, the emission layer (EML) is not only the placewhere excitons emerge and recombine to light emission but also shoulder the roleof transporting carriers (holes and electrons). Here, electrons and holes arerespectively injected from the cathode side and anode side, and then directlytransported to the EML where excitons are established and recombine to lightemission.Firstly, we fabricated a device without hole injection layer (HIL) and deviceswith different HILs adopting MoO3and PEDOT:PSS. The general device structureis ITO/HIL/POAPF:Firpic (10%,100nm)/LiF (0.5nm)/Mg:Ag. The device usingPEDOT:PSS as HIL material manifested best device performance. With similardevice structure, green and red SLOLEDs are also fabricated. As to the blueSLOLED, its’ EL spectra denotes stronger side emission compared with that of theconventional multilayer blue devices adopting Firpic as blue emitter. To explorethis phenomenon, we adjusted the EML thickness of the blue SLOLED andfabricated another four blue SLOLEDs with EML thickness to be60,70,80, and90nm. With the changing in EML thickness, the device EL spectra of the five blueSLOLEDs also changed and denoted decreased side emission with the EMLthickness becoming thinner. Here, the one with EML thickness to70nm manifested higher device efficiency and almost same EL properties as that of theconventional multilayer ones. Besides, theoretical simulation and experimentalresearch are implemented about this phenomenon, and we find it’s arisen from theweaker micro-cavity effect inside the device structure.Basing on above results, three sets of white SLOLEDs are fabricated byco-doping three different orange emitters (those are PO-01, PQ2Ir, andIr(BT)2acac) with Firpic into the same host material with the EML thickness fixedat70nm. Among these three sets of white SLOLEDs, the devices adopting PO-01and Firpic exhibit highest device efficiency with power efficiency of20.9lm/W at1000cd/m2and14.5lm/W at5000cd/m2. Nevertheless, white devices usingIr(BT)2acac and Firpic show best EL properties and almost no change in ELspectra along with device driving voltage.At last, considering that PEDOT:PSS is an acidic material of which has a badinfluence on device stability, so we determine to replace it with another HILmaterial and here select HAT-CN. The general device structure is ITO/HAT-CN(xnm)/POAPF:Firpic (10%,100nm)/LiF (0.5nm)/Mg:Ag. The function ofHAT-CN in injecting holes is researched by adjusting its’ thickness and the deviceperformance tend to become worse when the thickness excludes10nm. When thethickness of the HAT-CN layer is3nm, the device manifested excellent deviceperformance which can be comparable with those of the device adoptingPEDOT:PSS as HIL material.