Estrutura, propriedades e efeitos de envelhecimento do iodeto de chumbo e metilamônio parcialmente substituído com guanidínio
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2022-11-25
Autores
Minussi, Fernando Brondani
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Universidade Estadual Paulista (Unesp)
Resumo
As perovskitas de haletos (HPs) são uma classe de materiais conhecida por combinar inúmeras propriedades intrigantes, que advêm de diferentes possibilidades de composições e rotas de síntese, e lhes confere flexibilidade em aplicações. Embora tenham o potencial de revolucionar a optoeletrônica, perspectivas comerciais são limitadas pela instabilidade de seus dispositivos. Fatores comuns que levam à sua degradação são a exposição à umidade, oxigênio, luz e altas temperaturas. Em geral, estudos sobre a estabilidade de HPs são realizados em condições de degradação forçada, em filmes finos e/ou dispositivos, nos quais a presença de diferentes camadas pode alterar a forma como o material se transforma ao longo do tempo. Porém, pouco se conhece sobre possíveis modificações que as HP podem sofrem em condições não forçadas de degradação. Nesse cenário, o desenvolvimento de sistemas de cátions mistos vem se destacando como estratégia para alcançar propriedades otimizadas aliadas à maior estabilidade. Nos últimos anos, interesse tem sido dedicado ao estudo dos efeitos da incorporação de guanidínio (GA+) em várias HPs. Em particular, seu uso como um cátion substituto no iodeto de chumbo de metilamônio (MAPbI3) resultou em propriedades aprimoradas e, como consequência, em dispositivos mais eficientes e estáveis. Apesar disso, informações contraditórias ou inexistentes no sistema de iodeto de chumbo e metilamônio parcialmente substituído com guanidínio (GAxMA1-xPbI3) atrasam conquistas ainda melhores. No presente trabalho, demonstrou-se que soluções sólidas de GAxMA1-xPbI3 possuem temperaturas de transição de fase dependentes da concentração de GA+ e que a permissividade dielétrica e a condutividade iônica diminuem, enquanto os tempos de relaxação aumentam com a substituição GA+. Por sua vez, as energias de ativação para migração iônica passam por um máximo em concentrações intermediárias de GA+. Por meio de um procedimento de envelhecimento no escuro sob condições brandas de umidade e temperatura por 6 meses, foram investigadas as mudanças intrínsecas que composições desse sistema podem sofrer. Foram avaliadas mudanças estruturais (composição de fase e parâmetros de rede), microestruturais (tamanhos de grão) e elétricas (energias de band gap, histerese I-V, condutividade iônica, tempos de relaxação, mobilidade de portadores e densidades de portadores e de armadilhas eletrônicas). Mostrou-se que o comportamento de envelhecimento pode ser afetado não apenas pela presença de cátions de GA+, mas também por suas concentrações.
Halide perovskites (HPs) are a class of materials known to combine numerous intriguing properties, which come from different possibilities of compositions and synthesis routes, and give them flexibility in applications. While they have the potential to revolutionize optoelectronics, commercial prospects are limited by the instability of their devices. Common factors that lead to their degradation are exposure to moisture, oxygen, light and high temperatures. In general, studies on the stability of HPs are carried out under conditions of forced degradation, in thin films and/or devices, in which the presence of different layers can change the way the material transforms over time. However, little is known about possible changes that HP can undergo under unforced degradation conditions. In this scenario, the development of mixed cation systems has been highlighted as a strategy to achieve optimized properties allied to greater stability. In recent years, interest has been devoted to studying the effects of guanidinium (GA+ ) incorporation in various HPs. In particular, its use as a surrogate cation in methylammonium lead iodide (MAPbI3) has resulted in improved properties and, as a consequence, in more efficient and stable devices. Despite this, contradictory or non-existent information on the system of lead iodide and methylammonium partially substituted with guanidinium (GAxMA1-xPbI3) delay even better achievements. In the present work, it was demonstrated that solid solutions of GAxMA1-xPbI3 have phase transition temperatures dependent on the concentration of GA+ and that the dielectric permittivity and ionic conductivity decrease, while the relaxation times increase with GA+ substitution. In turn, activation energies for ion migration pass through a maximum at intermediate concentrations of GA+ . Through a dark aging procedure under mild conditions of humidity and temperature for six months, the intrinsic changes that compositions of this system can undergo were investigated. Structural (phase composition and lattice parameters), microstructural (grain sizes) and electrical (band gap energies, 𝐼������-𝑉������ hysteresis, ionic conductivity, relaxation times, carrier mobility and densities of carriers and electronic traps) were evaluated. It was shown that aging behavior can be affected not only by the presence of GA+ cations, but also by their concentrations.
Halide perovskites (HPs) are a class of materials known to combine numerous intriguing properties, which come from different possibilities of compositions and synthesis routes, and give them flexibility in applications. While they have the potential to revolutionize optoelectronics, commercial prospects are limited by the instability of their devices. Common factors that lead to their degradation are exposure to moisture, oxygen, light and high temperatures. In general, studies on the stability of HPs are carried out under conditions of forced degradation, in thin films and/or devices, in which the presence of different layers can change the way the material transforms over time. However, little is known about possible changes that HP can undergo under unforced degradation conditions. In this scenario, the development of mixed cation systems has been highlighted as a strategy to achieve optimized properties allied to greater stability. In recent years, interest has been devoted to studying the effects of guanidinium (GA+ ) incorporation in various HPs. In particular, its use as a surrogate cation in methylammonium lead iodide (MAPbI3) has resulted in improved properties and, as a consequence, in more efficient and stable devices. Despite this, contradictory or non-existent information on the system of lead iodide and methylammonium partially substituted with guanidinium (GAxMA1-xPbI3) delay even better achievements. In the present work, it was demonstrated that solid solutions of GAxMA1-xPbI3 have phase transition temperatures dependent on the concentration of GA+ and that the dielectric permittivity and ionic conductivity decrease, while the relaxation times increase with GA+ substitution. In turn, activation energies for ion migration pass through a maximum at intermediate concentrations of GA+ . Through a dark aging procedure under mild conditions of humidity and temperature for six months, the intrinsic changes that compositions of this system can undergo were investigated. Structural (phase composition and lattice parameters), microstructural (grain sizes) and electrical (band gap energies, 𝐼������-𝑉������ hysteresis, ionic conductivity, relaxation times, carrier mobility and densities of carriers and electronic traps) were evaluated. It was shown that aging behavior can be affected not only by the presence of GA+ cations, but also by their concentrations.
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Guanidínio, Perovskitas de haleto, Estrutura e propriedades, Envelhecimento, Halide perovskites, Guanidinium, Structure and properties, Aging