Síntese de óxidos de Perovskitas ferroelétricas para aplicações fotovoltaicas
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2024-03-15
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Universidade Estadual Paulista (Unesp)
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Semicondutores ferroelétricos com estrutura da perovskita capazes de absorver a luz visível, tem atraído interesse cientifico e tecnológico, devido a apresentarem valores baixos de band gaps (Eg), próximos do valor ótimo teórico de aproximadamente 1,4 eV. É bem conhecido que os semicondutores que absorvem luz visível e ultravioleta são amplamente utilizados em dispositivos fotovoltaicos, desta maneira, tem encorajado a aplicação desses materiais na camada ativa de células solares. Óxidos ferroelétricos geralmente possuem elevados band gaps (2,7-4 eV), o que só permite o aproveitamento de 8-20% do espectro solar. No entanto, o desenvolvimento de novos semicondutores ferroelétricos capazes de absorver a luz visível, particularmente a solução sólida com estrutura perovskita [KNbO3]x−1[BaNi0,5Nb0,5O3−δ] x, chamada de KBNNO, possuem um intervalo de band-gap direto amplamente ajustável, onde ao variar a composição de x = 0,1 a 0,5, obteve-se o material dopado com band-gaps na faixa de 1,18 a 2 eV. Para a composição x = 0,1, obteve-se Eg=1,39 eV, valor próximo do ideal para absorção da luz visível. Rotas de sínteses simples, com etapas, tempos e temperaturas reduzidas são essenciais para o progresso da aplicação de tais óxidos ferroelétricos em células solares. Em vista disso, neste trabalho, reporta-se a síntese da solução solida baseadas em KBNNO com x=0,1 e 0,05, chamadas de 0.1KBNNO e 0.05KBNNO, respetivamente, tanto pelo método por reação de estado sólido quanto pelo método de poliol modificado. Um conjunto de técnicas foi utilizado para a caracterização das amostras e os resultados mostraram que o método de reação de estado sólido foi mais eficiente na obtenção do material. Foi observado das medidas Raman que todas as amostras apresentam ferroeletricidade. A cor verde da amostra é um indicativo da menor energia do band-gap, que o do KNbO3, que é branco. Os espectros de impedância elétrica apresentadas por estes materiais estão diretamente associadas a relaxações do tipo não Debye. A condutividade DC para os compostos sintetizado pelo método por reação de estado sólido apresentam valores superiores que as sintetizadas pelo método de poliol.
Ferroelectric semiconductors with perovskite structure capable of absorbing visible light have attracted scientific and technological interest, due to their low band-gap (Eg) values, close to the optimal theoretical value of approximately 1.4 eV. It is well known that semiconductors that absorb visible and ultraviolet light are widely used in photovoltaic devices, thus, it has encouraged the application of these materials in the active layer of solar cells. Ferroelectric oxides generally have high band-gaps (2.7-4 eV), which only allows the use of 8-20% of the solar spectrum. However, the development of new ferroelectric semiconductors capable of absorbing visible light, particularly solid solution with perovskite structure [KNbO3]x−1[BaNi0,5Nb0,5O3−δ] x call from KBNNO; have a broadly adjustable direct band-gap range, where by varying the composition from x=0.1 to 0.5, the authors obtained the doped material with band-gaps in the range of 1.18 to 2 eV. For the composition x=0.1, Eg=1.39 eV was obtained, a value close to the ideal for absorption of visible light. Simple synthesis routes, with steps, times and reduced temperatures are essential for the progress of the application of such ferroelectric oxides in solar cells. In view of this, in this work, we report the synthesis of solid solution based on KBNNO with x=0,1 e 0,05, called 0.1KBNNO and 0.05KBNNO, respectively, both by the solid state reaction method and the modified polyol method. A set of techniques was used to characterize the samples and the results showed that the solid state reaction method was more efficient in obtaining the material. It was observed from the Raman measurements that all samples present ferroelectricity. The green color of the sample is an indication of the lower band-gap energy than that of KNbO3, which is white. The electrical impedance spectra presented by these materials are directly associated with non-Debye type relaxations. The DC conductivity for compounds synthesized by the solid state reaction method presents higher values than those synthesized by the polyol method.
Ferroelectric semiconductors with perovskite structure capable of absorbing visible light have attracted scientific and technological interest, due to their low band-gap (Eg) values, close to the optimal theoretical value of approximately 1.4 eV. It is well known that semiconductors that absorb visible and ultraviolet light are widely used in photovoltaic devices, thus, it has encouraged the application of these materials in the active layer of solar cells. Ferroelectric oxides generally have high band-gaps (2.7-4 eV), which only allows the use of 8-20% of the solar spectrum. However, the development of new ferroelectric semiconductors capable of absorbing visible light, particularly solid solution with perovskite structure [KNbO3]x−1[BaNi0,5Nb0,5O3−δ] x call from KBNNO; have a broadly adjustable direct band-gap range, where by varying the composition from x=0.1 to 0.5, the authors obtained the doped material with band-gaps in the range of 1.18 to 2 eV. For the composition x=0.1, Eg=1.39 eV was obtained, a value close to the ideal for absorption of visible light. Simple synthesis routes, with steps, times and reduced temperatures are essential for the progress of the application of such ferroelectric oxides in solar cells. In view of this, in this work, we report the synthesis of solid solution based on KBNNO with x=0,1 e 0,05, called 0.1KBNNO and 0.05KBNNO, respectively, both by the solid state reaction method and the modified polyol method. A set of techniques was used to characterize the samples and the results showed that the solid state reaction method was more efficient in obtaining the material. It was observed from the Raman measurements that all samples present ferroelectricity. The green color of the sample is an indication of the lower band-gap energy than that of KNbO3, which is white. The electrical impedance spectra presented by these materials are directly associated with non-Debye type relaxations. The DC conductivity for compounds synthesized by the solid state reaction method presents higher values than those synthesized by the polyol method.
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Palavras-chave
Ferroelétrico, Perovskita, Reação de estado sólido, Poliol modificado, Ferroelectric, Perovskite, Solid state reaction, Modified polyol, KBNNO
Como citar
ALFARO, Jhonatan Alfaro. Síntese de óxidos de Perovskitas ferroelétricas para aplicações fotovoltaicas. Orientador: Silvio Rainho Teixeira. 2024. 93 f. Dissertação (Mestrado em Ciência e Tecnologia de Materiais) - Faculdade de Ciências e Tecnologia, Universidade Estadual Paulista, Presidente Prudente, 2024.