| Summary: | 碩士 === 國立成功大學 === 光電科學與工程研究所 === 93 === By the development of the intelligent industry, people have more require for the monitor. Although the CRT is low-cost and good image quality, the CRT is too big and too heavy. Therefore, the new flat panel displays (FPD) have to be thinner and lighter. In this age, polymer light-emitting diodes (PLED) that are based on conjugated polymers have attracted much attention because of their potential applicability to large-area flat panel displays (FPD). Because polymeric materials are known to be sensitive, therefore, various approaches have been explored to improve the device efficiency and luminescence. In this work, an effect of thermal treatment before cathode deposition and post cathode deposition are presented for the purpose of achieving a high efficiency Polymer light-emitting diodes by change the roughness and the chain intensity.
At first, the devices had been made as ITO/PEDOT:PSS /DBPPV/Ca/Al. The PEDOT:PSS served as HTL and DBPPV served as EL. And, the glass transition temperature of DBPPV was about 120°C ~130°C. On the one hand, the device pre-annealed at 120oC had been demonstrated to have better performance than other pre-annealed devices. For example, the current efficiency was 2.58CD/A of the pre-annealed at 120°C device, just below the Tg, while the devices annealed at RT, 90°C, 150°C and 180°C is only 2.1, 1.98, 1.91 and 1.74 cd/A, respectively. And, there were a little influence for the turn-on voltage and spectrum when pre-annealed temperature below Tg. For example, the turn-on voltage was 2.9V, 3.0V, 3.0V, 3.48V, 3.6V while the devices pre-annealed at RT, 90°C, 120°C, 150°C and 180°C and the main EL peak were 524nm, 527nm, 530nm, 550nm and 545nm. On the other hand, the device post-annealed at 120oC has the best performance than the device pre-annealed at 120oC. For example, the current efficiency was 3.04CD/A of the post-annealed at 120°C device. It was considered have two reasons. The first is post heat treatment may improve the adhesion of the polymer/electrode interface which made for the effective injection of an electron. The other is on the cathode side, the metallic atoms may diffused into the polymer surface. So the orientation of the polymer chain may have little effect to electron injection. Therefore, the post-annealed EL devices give off more bright light at high electric fields than pre-annealed one. And, the maximum luminance is 30871cd/m2 @ 8.89V 105mA.
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