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Fabrication and Characterization of Perovskite-Based Photodetectors
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Com o rápido avanço dos sistemas de visão computacional surge a necessidade de desenvolvimento de sensores de maior resolução. Os sensores de imagem tradicionais, com filtros Bayer, utilizam 30% da luz incidente, para resolver este problema desenvolveu-se um guia de onda que divide o espectro por comprimentos de onda, permitindo a deteção de até 90% da luz. Este maior aproveitamento potencia uma redução significativa das dimensões dos pixéis, tornando a utilização de silício inadequada devido ao efeito de crosstalk. Com o intuito de minimizar este efeito, as tecnologias de filmes finos oferecem uma solução viável, em simultâneo estas aplicações exigem que o material converta, eficazmente, o espectro visível e que possa resistir a elevadas amplitudes térmicas. A perovskite inorgânica surge como um candidato ideal, graças ao seu elevado coeficiente de absorção e ao seu hiato ótico adequado.
Inicialmente, utilizámos perovskite CsPbI3 dopada com iodeto de dimetilamónio, depositada por spin coating, onde explorámos os efeitos da dopagem na performance do dispositivo. De forma a melhorar a eficiência, recorremos a TiO2 e C60, individualmente, como camada de transporte de electrões e testámos uma abordagem de camada dupla que combina um material à base de carbono com um óxido, para evitar a difusão de iões metálicos e, consecutivamente, dispositivos shunted. Neste estudo, a referecia demonstrou uma dark current da ordem dos 10-7 A/cm2 e valores de eficiência quântica externa de cerca de 50%. Numa segunda fase, a atenção foi direcionada para perovskite CsPbI2Br co-evaporada. Investigámos o efeito da rate de deposição total (de 0,8 Å/s a 1,6 Å/s) e o efeito do rácio molar de co-evaporação CsBr:PbI2 (de 0,80:1,00 a 1,20:1,00). Adicionalmente, explorámos a introdução de camadas intermédias de CsBr e PbI2 entre a perovskite e as camadas de transporte, para melhorar o transporte de carga e reduzir a variabilidade nas curvas JV. A referência para estes testes demonstrou uma dark current na ordem dos 10-6 A/cm2 e valores de EQE em torno de 80%. Para a caraterização de filmes e de dispositivos foram utilizadas várias técnicas, incluindo a microscopia de força atómica e várias técnicas de caraterização eléctrica. Por fim, foi implementada uma análise Mott-Schottky de condensadores metal-isolador-semicondutor para retirar a dopagem e a concentração de portadores. Após experiências com quantum dots de PbS e filmes de perovskite, foi possivel medir concentrações de portadores na ordem de 1015 cm-3, porem, medições mais perto de níveis intrínsecos continuam a ser um desafio.
The rapid advancement of computer vision systems has created a demand for higher resolution imagers. Traditional image sensors with Bayer filters only utilize 30% of incoming light. To address this, efforts have been taken to develop a color-splitting waveguide that enables the detection of up to 90% of the light. However, the significant size reduction renders silicon technology unsuitable due to crosstalk effect. Thin-film technology presents a viable solution to minimize this crosstalk. For these applications, we require a material that efficiently converts visible light and can withstand high thermal budgets. Inorganic perovskite emerges as one ideal candidate, thanks to its high absorption coefficient and suitable bandgap. Our first focus was on spin-coated dimethylammonium iodide doped CsPbI3 perovskite, where we explored the effects of doping on device performance. To further improve efficiency, we used TiO2 and C60 individually for the electron transport layer and tested a double-layer approach combining a carbon-based material with an oxide to prevent metal ion diffusion and shunted devices. In this study the baseline demonstrated dark currents on the order of 10-7 A/cm2 and external quantum efficiency (EQE) values around 50%. In the second phase, attention was shifted to co-evaporated CsPbI2Br perovskite. We investigated the effect of total deposition rate (from 0.8 Å/s to 1.6 Å/s), and the effect of the CsBr:PbI2 co-evaporation molar ratio (from 0.80:1.00 to 1.20:1.00). Additionally, we introduced interlayers of CsBr and PbI2 between the perovskite and transport layers to improve charge transport and reduce variability in the JV characteristics. The baseline for these tests demonstrated dark currents on the order of 10-6 A/cm2 and EQE values around 80%. For film and device characterization, we employed various measurements, including Atomic Force Microscopy and various electrical characterizations techniques. Furthermore, we implemented Mott-Schottky analysis of metal-insulator-semiconductor capacitors to assess doping and carrier concentration. After experimenting with PbS quantum dots and perovskite films, we could measure carrier concentrations as low as 1015 cm-3, but accurate measurements near intrinsic levels remain challenging.
The rapid advancement of computer vision systems has created a demand for higher resolution imagers. Traditional image sensors with Bayer filters only utilize 30% of incoming light. To address this, efforts have been taken to develop a color-splitting waveguide that enables the detection of up to 90% of the light. However, the significant size reduction renders silicon technology unsuitable due to crosstalk effect. Thin-film technology presents a viable solution to minimize this crosstalk. For these applications, we require a material that efficiently converts visible light and can withstand high thermal budgets. Inorganic perovskite emerges as one ideal candidate, thanks to its high absorption coefficient and suitable bandgap. Our first focus was on spin-coated dimethylammonium iodide doped CsPbI3 perovskite, where we explored the effects of doping on device performance. To further improve efficiency, we used TiO2 and C60 individually for the electron transport layer and tested a double-layer approach combining a carbon-based material with an oxide to prevent metal ion diffusion and shunted devices. In this study the baseline demonstrated dark currents on the order of 10-7 A/cm2 and external quantum efficiency (EQE) values around 50%. In the second phase, attention was shifted to co-evaporated CsPbI2Br perovskite. We investigated the effect of total deposition rate (from 0.8 Å/s to 1.6 Å/s), and the effect of the CsBr:PbI2 co-evaporation molar ratio (from 0.80:1.00 to 1.20:1.00). Additionally, we introduced interlayers of CsBr and PbI2 between the perovskite and transport layers to improve charge transport and reduce variability in the JV characteristics. The baseline for these tests demonstrated dark currents on the order of 10-6 A/cm2 and EQE values around 80%. For film and device characterization, we employed various measurements, including Atomic Force Microscopy and various electrical characterizations techniques. Furthermore, we implemented Mott-Schottky analysis of metal-insulator-semiconductor capacitors to assess doping and carrier concentration. After experimenting with PbS quantum dots and perovskite films, we could measure carrier concentrations as low as 1015 cm-3, but accurate measurements near intrinsic levels remain challenging.
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Palavras-chave
Photodetectors inorganic perovskites charge transport layers metal-insulator-semiconductor capacitors