Estrutura eletrônica de materiais empregados na camada ativa de células eletroquímicas poliméricas emissoras de luz
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Data
2019-03-29
Autores
Galindo, Levy Alvarenga
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O uso de materiais orgânicos em dispositivos optoeletrônicos tornou-se atraente devido a vários fatores, como o baixo custo de obtenção do produto final, bem como a leveza e a flexibilidade dos dispositivos produzidos. Dentre estes dispositivos incluem-se as células eletroquímicas poliméricas emissoras de luz (PLECs). Tais dispositivos eletrônicos emissores de luz orgânicos são compostos de uma blenda entre um polímero semicondutor e um eletrólito contendo um sal e um condutor iônico polimérico. No entanto, alguns dos mecanismos básicos envolvidos na operação destes dispositivos ainda não são completamente compreendidos. De fato, é bem conhecido que interações específicas envolvendo o polímero semicondutor e o sal iônico desempenham um papel importante de transporte de carga, mesmo sem a plena compreensão dos detalhes associados a essas interações. Neste contexto, aqui relatamos uma abordagem teórica que visa desvendar aspectos básicos sobre o assunto. Para tanto, as propriedades estruturais e de reatividade do polímero semicondutor poli [(9,9-dioctilfluorenil-2,7-diil)-co-(1,4-vinilenofenileno)] e do sal triflato de lítio foram avaliados através de cálculos de estrutura eletrônica empregando o Método Paramétrico 3 (PM3) (abordagem semi-empírica) e a Teoria do Funcional da Densidade (usando o funcional de correlação e troca B3LYP e o conjunto de base 6-31G). Para identificar os locais onde as interações polímero-sal ocorrem preferencialmente, cálculos de reatividade local foram realizados empregando-se os Índices de Fukui condensados-aos-átomos. Os resultados obtidos sugerem que a presença de íons do sal induz alterações significativas nas propriedades eletrônicas do polímero semicondutor, as quais dependem da densidade relativa de íons e do estado de oxidação do polímero, facilitando a injeção e o transporte da carga nos dispositivos. A partir dos cálculos de reatividade e adsorção, importantes limites já experimentalmente identificados, associados à concentração de sal nos sistemas puderam ser interpretados, bem como detalhes acerca do mecanismo de funcionamento das PLECs em diferentes regimes de tensão.
The use of organic materials in optoelectronic devices has become attractive due to several factors, such as the low cost of the final products, as well as the lightness and flexibility of the resulting devices. These devices include polymer light emitting electrochemical cells (PLECs). Such organic light-emitting devices are based on a blend that includes a semiconductor polymer, a salt and an ionic conductor. However, some of the basic mechanisms involved in the operation of these devices are still not completely understood. Indeed, it is well known that specific interactions involving the semiconducting polymer and the ionic salts play an important role in the charge transport, even without the full understanding of the associated details of these interactions. In this context, we report a theoretical approach that aims to uncover basic aspects about the subject. Therefore, the structural and reactivity properties of the semiconductor polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-vinylenephenylene)] and lithium triflate salt were evaluated via electronic structure calculations employing Parametric Method 3 (PM3) semi-empirical approach and Density Functional Theory (using B3LYP exchange-correlation functional and 6-31G basis set). To identify the sites where polymer-salt interactions occur, local reactivity calculations were performed employing Condensed-to-atoms Fukui Indexes. The obtained results suggest that the presence the salt ions induces significant changes on electronic properties of the semiconducting polymer, which are dependent on the relative density of ions and oxidation state of the polymer, facilitating the charge injection and transport in the devices. From the calculations of reactivity and adsorption, important limits already experimentally identified, associated with salt concentration in the systems could be interpreted, as well as details on the mechanism of operation of PLECs in different voltage regimes.
The use of organic materials in optoelectronic devices has become attractive due to several factors, such as the low cost of the final products, as well as the lightness and flexibility of the resulting devices. These devices include polymer light emitting electrochemical cells (PLECs). Such organic light-emitting devices are based on a blend that includes a semiconductor polymer, a salt and an ionic conductor. However, some of the basic mechanisms involved in the operation of these devices are still not completely understood. Indeed, it is well known that specific interactions involving the semiconducting polymer and the ionic salts play an important role in the charge transport, even without the full understanding of the associated details of these interactions. In this context, we report a theoretical approach that aims to uncover basic aspects about the subject. Therefore, the structural and reactivity properties of the semiconductor polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-vinylenephenylene)] and lithium triflate salt were evaluated via electronic structure calculations employing Parametric Method 3 (PM3) semi-empirical approach and Density Functional Theory (using B3LYP exchange-correlation functional and 6-31G basis set). To identify the sites where polymer-salt interactions occur, local reactivity calculations were performed employing Condensed-to-atoms Fukui Indexes. The obtained results suggest that the presence the salt ions induces significant changes on electronic properties of the semiconducting polymer, which are dependent on the relative density of ions and oxidation state of the polymer, facilitating the charge injection and transport in the devices. From the calculations of reactivity and adsorption, important limits already experimentally identified, associated with salt concentration in the systems could be interpreted, as well as details on the mechanism of operation of PLECs in different voltage regimes.
Descrição
Palavras-chave
PLECs, Polímero semicondutor, Sal, Índices de reatividade, Semiconductor polymer, Salt, Reactivity indexes