Enhancement of photoluminescence in conjugated polymer thin film induced by molecular packing、dewetting and stretching

• Main Authors: Lee, Pei-Wei, 李培煒
• Other Authors: 楊長謀
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/85012666235135491533

碩士 === 國立清華大學 === 材料科學工程學系 === 99 === Enhancement of photoluminescence in conjugated polymer thin film induced by chain packing, dewetting and stretching was investigated in the thesis. At first, by varying the parameter in spin casting we found that molecular chain packing was highly sensitive to the condensation process owing to the π-π interactions at the backbone of conjugated polymer, MEH-PPV. Grazing-angle x-ray reflectivity data revealed the bi-layered structures in the ultrathin polymer films which showed strong dependence on the van der Waals interactions from the substrate and illustrated various PL efficiencies. Second, long distance flow and shearing in MEH-PPV molecular chain during thermal dewetting prevailed the reduction of electron-phonon coupling which resulted in large PL enhancement. The blue shifting PL spectra was attributed by molecular constraint and separation on the substrates during dewetting. By measuring grazing-angle x-ray reflectivity and con-focal PL spectra, it found that largest luminescenece efficiency and exciton quenching switching-off at the dissociative heterojunction took place in ~2 nm dewetting residual film. Dewetting droplets also showed PL enhancement resulted by accumulating the moelcuar chain flowed and sheared in dewetting processes, however, the poor survival time was resulted from chain relaxation and degradation. Furthermore, effective reduction of non-radiactive relaxation in flowed and constrained MEH-PPV polymer chains by dewetting behavior resulted in increased exciton lifetime and enhanced PL effeciecny was invesigated by TCSPC system. Finally, the suppression of electron-phonon interaction also investigated by measurement of polarized fluorescence emission and magneto-optical effect in stretched conjugated polymer film. Fluorescence enhancement of intra-chain emission was obviously exhibited at the parallel direction of polarized excited laser and tension. These research bear important implications for the exploration of fundamental optoelectronic properties of conjugated polymers and their applications in polymer-based devices.