Estudo das propriedade elétricas e luminescentes de blendas poliméricas aplicadas a células eletroquímicas emissoras de luz
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Data
2017-08-18
Autores
Canassa, Thalita Antoniassi [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Células eletroquímicas emissoras de luz (LECs) são dispositivos eletroluminescentes orgânicos que apresentam várias vantagens em relação aos tradicionais diodos emissores de luz poliméricos (PLEDs). Em geral, as LECs apresentam uma baixa tensão de operação, que é independente da função trabalho do eletrodo e uma maior eficiência devido à injeção de carga equilibrada dos eletrodos. A camada ativa de LEC geralmente compreende uma mistura de um polímero conjugado eletroluminescente e um eletrólito polimérico sólido, ocorrendo uma combinação de transporte iônico e eletrônico. Neste trabalho, estudamos as propriedades elétricas e ópticas do poli (3-hexiltiofeno), P3HT; poli (9,9-di-n-octilfluorenil-2,7-diil), PFO; poli [2-metoxi-5- (3 ', 7'-dimetiloctiloxi) -1,4-fenilenovinileno], MDMO-PPV e poli (óxido de etileno), PEO, essas blendas foram utilizadas para aplicações em LEC poliméricas. O estudo baseou-se nos resultados das medidas de corrente e luminância vs. tensão (I x V e L x V), espectroscopia no infravermelho (FTIR), espectroscopia na região do UV e do visível (UV-Vis) e espectroscopia de fluorescência de dispositivos produzidos em diferentes composições de blendas. As LECs foram produzidos em uma configuração do tipo sanduíche, usando filmes finos poliméricos com espessura variando entre 250 nm a 600 nm. O eletrólito polimérico da blenda compreende uma mistura de PEO com sal de trifluorometanossulfonato de lítio (triflato de lítio, CF3SO3Li), cuja relação de concentração (sal: PEO) variou de 0 a 10% (w: w). Os resultados mostraram que o comportamento bipolar elétrico é conseguido aumentando a concentração de sal (acima de 5%), resultando em melhor desempenho do dispositivo. Os experimentos de absorção e de fluorescência revelaram mudanças nos espectros com a adição do eletrólito polimérico na blenda, acompanhada por uma mudança na estrutura vibrônica dos espectros de excitação de fluorescência. Além disso, a análise da espectroscopia FTIR mostrou que, ao aumentar o teor de sal na mistura, o espectro vibracional do PEO é alterado, provavelmente devido à interação entre o sal e as ligações C-O do poliéter.
Light emitting electrochemical cells (LECs) are organic electroluminescent devices which present several advantages over traditional polymer light-emitting diodes (PLEDs). In general, LECs presents a low operation voltage, which is independent on the electrode work function and a higher efficiency due to the balanced charges injection from the electrodes. The active layer of LECs usually comprises a blend of a conjugated electroluminescent polymer and a solid polymeric electrolyte. In this work, we studied the electrical and optical properties of poly(3-hexylthiophene), P3HT; poly(9,9-di-n-octylfluorenyl-2,7-diyl), PFO; poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene], MDMO-PPV, and poly(ethylene oxide), PEO, blends for polymeric LECs applications. The study was based on results from current and luminance vs. voltage (I x V and L x V), FTIR, UV-Vis and Fluorescence spectroscopy measurements of devices produced at different blend compositions. The LECs were produced in a sandwich type configuration, by using polymeric thin films with thickness varying from 250 nm to 600 nm. The blend polymeric electrolyte comprises a PEO mixture with lithium trifluoromethanesulfonate salt (lithium triflate, CF3SO3Li), which concentration ratio (salt:PEO) varied from null to 10% (w:w). The results showed that electric bipolar behavior is achieved by increasing the salt concentration (above 5%), resulting in improved device performance. The UV-vis absorption and fluorescence spectra revealed a noticeable red-shift in the energy bandgap with the addition of the polymeric electrolyte in the blend, accompanied by a change in the vibronic structure of the fluorescence excitation spectra. Moreover, FTIR spectroscopy analysis showed that, by increasing the salt content in the blend, the vibrational spectrum of PEO is changed, probably due to the interaction between the salt and the C-O bonds of the polyether.
Light emitting electrochemical cells (LECs) are organic electroluminescent devices which present several advantages over traditional polymer light-emitting diodes (PLEDs). In general, LECs presents a low operation voltage, which is independent on the electrode work function and a higher efficiency due to the balanced charges injection from the electrodes. The active layer of LECs usually comprises a blend of a conjugated electroluminescent polymer and a solid polymeric electrolyte. In this work, we studied the electrical and optical properties of poly(3-hexylthiophene), P3HT; poly(9,9-di-n-octylfluorenyl-2,7-diyl), PFO; poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene], MDMO-PPV, and poly(ethylene oxide), PEO, blends for polymeric LECs applications. The study was based on results from current and luminance vs. voltage (I x V and L x V), FTIR, UV-Vis and Fluorescence spectroscopy measurements of devices produced at different blend compositions. The LECs were produced in a sandwich type configuration, by using polymeric thin films with thickness varying from 250 nm to 600 nm. The blend polymeric electrolyte comprises a PEO mixture with lithium trifluoromethanesulfonate salt (lithium triflate, CF3SO3Li), which concentration ratio (salt:PEO) varied from null to 10% (w:w). The results showed that electric bipolar behavior is achieved by increasing the salt concentration (above 5%), resulting in improved device performance. The UV-vis absorption and fluorescence spectra revealed a noticeable red-shift in the energy bandgap with the addition of the polymeric electrolyte in the blend, accompanied by a change in the vibronic structure of the fluorescence excitation spectra. Moreover, FTIR spectroscopy analysis showed that, by increasing the salt content in the blend, the vibrational spectrum of PEO is changed, probably due to the interaction between the salt and the C-O bonds of the polyether.
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Palavras-chave
Células eletroquímicas emissoras de luz, Diodos emissores de luz poliméricos, Propriedades ópticas, Light emitting electrochemical cells, Polymer light-emitting diodes, Optical properties