Electrodeposited Patterning Organic Luminescent Films And Their Applications For Display Devices

In situ electrochemical deposition (ED) approach for fabricating conducting polymernetwork films has exhibited great potential applications in optoelectronic devices, such asorganic light-emitting diodes (OLEDs) and photovoltaic cells. In this method, thepolymerization degree, thickness and morphology of ED films can be easily modulatedby controlling ED conditions including the preparation techniques and experimentalparameters. Most importantly, ED can combine the synthesis and in situ deposition ofpolymer films in the target electrode in one step. In principle, ED can be used to fabricatepatterning organic luminescent films for low-cost and high-resolution OLEDs.Unfortunately, there are rarely reports on the preparation and application of organicluminescent ED films with high performance due to their intrinsic low luminousefficiency. Recently, great progress has been made by Prof. Ma et al., who successfullyobtained high luminescent ED films and devices by proper designing high-fluorescentsmall-molecules containing electroactive carbazole units and precisely optimizing EDconditions. Despite substantial progresses in the field of organic luminescent ED filmshave been gained during the last few years, there are still some crucial problems both inscience and technology needed to be resolved, such as precise control of the chemicaland condensed structures of ED films, preparation of high-quality patterning ED films,deep understanding of factors influencing the stability of ED OLEDs and combination of ED techniques and TFT processing for AMOLEDs. Based on these considerations, herein,we demonstrated several methods to resolve these problems.Firstly, we developed two methods based on molecular design and electrode-surfacemodification to realize the precise control of the structure of ED films.On the one hand, we utilized multifunctional fluorene-based precursors to constructhighly cross-linked and compact luminescent ED films for highly efficient and stableelectroluminescence devices. The systematical study of structure-property relationsreveal that increasing the functionality of ED precursors are very effective at improvingthe film growth rate, promoting the cross-linking degree as well as enhancing theuniformity and packing density of final EP films. Such improvements in the structure ofEP films could be related to the increased heterogeneous electron-transfer rate. Thesecorrelations had possible implications in the design of novel precursors and gave us asimple and efficient method for modulating the structure and property of organicoptoelectronic films and devices.On the other hand, We used PEDOT:PSS modified ITO electrode to control thenucleation and deposition process. The ED film on modified electrode revealed alayer-by-layer growth mode, which dramatically increased the uniformity and density ofED films. Moreover, the leakage current of PEDOT:PSS modified ED device wasdecreased significantly. Finally, OCBzC ED device on modified ITO anode exhibitedhigh luminous efficiency up to9.5cd A-1, which was enhanced by80%in comparisonwith that on bare ITO anode.Secondly, We demonstrated a simple and efficient approach, based on themodification of electrode surface with electroactive SAMs, for fabricating patternedluminescent films on silicon electrodes, which had potential applications in flat displaydevices. In addition, this surface-modification method has also been extended andapplied in grafting ED films onto the electrode surface and subsequently increasing theefficiency and stability of ED devices. It was found that the close-packed electroactiveSAMs were effective at enhancing the work function of electrode, increasing thedeposition rate of EP precursors as well as promoting the cross-linking efficiency and the adhesion of following ED films.Thirdly, We introduced an idea that utilizing TFT as switch controls the selectiveelectrodeposition of luminescent molecules for the preparation of RGB full-color pixels.As an example, the first luminescent film were precisely electrochemical deposited intothe pixel pits of active matrix substrates (metal-oxide TFT (MOTFT) backplane). The EDfilms exhibited clear boundary and uniform surface morphology (RMS: ca.4.0nm)without―coffee-ring‖phenomenon that commonly observed in ink-jet printing. Inaddition, the technical scheme for constructing RGB luminescent films on active matrixsubstrate by ED method were given. We anticipate that ED technology will be useful inlow-cost and high-resolution AMOLED manufacturing in the near future.