Light Emitting Diodes of Heterocyclic Aromatic Rigid-Rod and Coil-Like Polymers

• Main Authors: Chin-Feng Chang, 張金鳳
• Other Authors: Shih-Jung Bai
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/54932031251719366488

碩士 === 國立中山大學 === 材料科學研究所 === 89 === ABSTRACT Optoelectronics of polymer light emitting diode (LED) depends significantly on polymer molecular structure and charge conjugation. This study focused on the optoelectronics of freestanding films and LEDs of a colinear, fully conjugated heterocyclic aromatic rigid-rod polymer (PBT) and its mixtures with a partially conjugated coil-like polymer (Pbi). A deuterated PBTd4 was also mixed with a fully conjugated coil-like polymer (ABPBI) for UV-Vis absorption spectrum, photoluminescence (PL), diodic current-voltage response, and electroluminescence (EL). Rigid-rod PBT was only soluble in strong protic acid. PBT films were processed using methanesulfonic acid. PBT free-standing films showed maximum absorptions at 468 nm and 640 nm; PBTd4 having all hydrogen atoms on the phenylene moiety substituted by deuterium retaining same electron orbitals thus showed same absorption and PL spectra. It was likewise for the PBTd4 and ABPBI mixtures at ABPBI concentrations of 1 % and 10 %. For mixtures of PBT and Pbi, the absorption spectra indicated super- position of individual optical absorption response and no energy transfer. However, PL spectra showed a blue shift with increasing Pbi content. This was attribed for PBT rod-like configuration, or PBT aggregation perturbed by mixing with Pbi. Monolayer LED of Al/PBT/ITO and Al/Pbi/ITO yielded a threshold voltage of 4 V. When PBT/Pbi mixtures of 75/25, 50/50, 25/75, were used as the light emitting layer, the threshold voltage altered to 10 V, 7 V and 17 V, respectively. This threshold voltage deviation from 4 V is due mainly to difference in layer thickness, or phase separation affecting the tunneling effect. To enhance LED stability, an Ag layer was evaporated onto the Al electron injection electrode. For Ag/Al/PBT/ITO devices and mixed PBT/Pbi (75/25,50/50,25/75) devices, the maximum EL wavelength exhibited no systematic change at 753 nm, 714 nm, 727 nm, and 697 nm, respectively, due to using different bias voltage.