Enhance efficiency of OLEDs by solution-processed small molecule electron transport layer & achieve all solution-processed OLEDs
Date Issued
2015
Date
2015
Author(s)
Chen, Wei-Ting
Abstract
In this thesis, we focus on fabricating all solution-processed organic light-emitting diode (OLED) with the ordinary commercial materials. Besides, Our OLED device is designed based on conventional structure, phosphorescence emitting materials and all organic layer with water insoluble feature (non-PEDOT:PSS). The thesis can be break into three parts. For the first part (chapter 3), our purpose is to fabricate solution-processed blue OLED with merely evaporated cathode on top of it (aluminum). We selected and optimized the proper hole transport layer, adjusted the percentage and concentration of the solution recepie in the emission layer. Also, by introducing the noval PF-NR2 materials as our electron injection layer, we successfully produced our standard blue OLED with all-solution processed organic layer. Through fine-tuning of the PF-NR2 fabrication process, the standard device achieved 8.18 cd/A as its highest current efficiency. For the second part (chapter 4), we try to improve the device efficiency of the first part by two means. First, we inserted an solution-processed interlayer between emission layer and hole transport layer to diminish exciton quenching effect. Second, we carfully tested and selected the solvent/electron transport materials combination, in order to fabricate a complete solution-processed electron transport layer upon emission layer. With incorporated solution-processed interlayer and electron transport layer into our OLED device, we enhanced our device performance to 12.78 cd/A. Which is about 1.56 times as much as the standard device in the first part. In the last part (chapter 5), we focused on making white emission layer and replacing evaporated cathode with solution-processed hybrid electrode. Since our previous studies (part 1 & 2) were using Firpic as the luminescent materials. We blended Ir(mppy)3 and Ir(piq)2 acac mateials into emission layer, to bring a white OLED emission layer of CIE (0.31, 0.37) under careful control of the emitting mateials ratio. On the other hand, we fabricate an innovative transparent cathode with simplified design. With the combination of graphene and silver nanowire, we surprisingly discovered a transparant, highly conductive, solution-processed cathode (hybrid electrode) that can be used in organic device. In the end, we literally produced an “all solution-process” transparent OLED, using the hybrid cathode of graphene & silver nanowire. That achieved 1.19 cd/A with one-sided emission measurement. (may be 2.41 cd/A if two-sided emission measured)
Subjects
Organic light-emitting diode (OLED)
solution-process
white OLED
graphene
silver nanowire (Ag nanowire)
commercial materials
Type
thesis
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