Study. Based On Silole Molecules In The Performance Of Organic Electroluminescent Devices

Organic light-emitting devices (OLED) have been one of the hottest topics in the flat panel display field. OLED have the advantages of flat panel, self-emission, full color, quick response, wide viewing angle and being easy to realize thinness and light weight, and thus is considered to be a novel technology most likely to replace liquid crystal display and plasma display panel in the near future. But some problems such as high production cost and low reproducibility remain to be solved. For the sake of the enhancement of optoelectronic performance of OLED based on small molecules especially Silole derivatives, in this work we focused on the systematic investigation of material preparation, device structure and basic theory. The main content is as follows:1. The background, development and luminescent mechanism of OLED are reviewed, which is the theoretical basis for relevant investigation in this work.2. The fabrication and improvement of blue devices have been carried out, which are based on NPB by using conventional organic materials with superior properties and by energy level matching of various organic layers as well as optimization of device structure. The results demonstrate that the introduction of hole blocking material bathocuproine (BCP) causes remarkable changes of device performance, confining charge carrier recombination zone within N, N'-diphenyl-N,N'-bis (3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB) layer. Device with the structure of indium tin oxide (ITO)/NPB/BCP/Mg:Ag reaches to a luminance of 6440 cd/m~2 at the voltage of 16 V, corresponding to a current density of 895.3 mA/cm~2, and a maximum luminance efficiency of 0.57 lm/W, showing that excellent blue emission of NPB was achieved.3. The absorption spectrum, Photoluminescent (PL) spectrum and device electroluminescent (EL) spectrum of novel Silole material 2,2,3,3- -4,4-bisthienylsilole (TPBTSi) are measured and analyzed. Green device with the structure of ITO/NPB/TPBTSi/Alq3/Mg:Ag, where Silole is used as an emitter, is fabricated by improving fabrication technique and optimizing film thickness. The maximum luminance is 11290 cd/m~2,the maximum luminance efficiency is 0.84 lm/W,and the peak of emissive spectrum is 516 nm,and the Commissions International d'Eclairage (CIE) coordinates locates at (0.275,0.4568),which is consistent with the characterized spectrum of TPBTSi.4. Yellow light-emitting device with 2,2,4,4-tetraphenyl-3,3-bisthienylsilole (TPB3TSi) as an emitter was studied. It was found that light emissive spectrum was located at 580 nm, and the maximum luminance of double and triple layer devices are 7508 and 1385 cd/m~2 (at a bias voltage of 17 V), respectively, when the thickness of TPB3TSi is 20 nm. But the device current density is relatively high, leading to the reduced luminance efficiency. This may be ascribed to the charge carrier traps of TPB3TSi (traps refer to the energy levels which have a higher ability of accepting electrons or holes) and low fluorescent efficiency.5. High performance OLED using two Silole derivatives 1,2-bis(1-methyl-2,3,4,5-tetraphenyl-1H-Silole-1-yl)ethane (BMPSiE) and 1,1′-dimethyl-3,3′,4,4′-tetraphenyl-2,2′5,5′-tetra(thiophen-2-yl)-1,1′-bi(1H-silole) (BMPThSi) as emitting materials which are processed by vacuum thermal evaporation method, NPB and tris(8-hydroxyquinolinolato) aluminum (Alq3) act as hole transporting layer (HTL) and electron transporting layer (ETL), respectively. The luminance-voltage and current density-voltage characteristics of devices are investigated, and their performance difference is discussed. The results demonstrate that at a bias voltage of 20 V, the devices consisting of novel emissive material BMPSiE and BMPThSi have a maximum luminance of 9992 and 15262 cd/m~2, respectively. The peaks of electroluminescence (EL) spectra locate at 483 and 495 nm, respectively, which are in good accordance with the PL characteristics of Siloles.