Academic literature on the topic 'MAPbCl3'

Hybrid perovskites, especially methylammonium lead iodide (MAPbI3), exhibit excellent solar power conversion efficiencies. However, their application is plagued by poor chemical and structural stability. Using direct calorimetric measurement of heats of formation, MAPbI3 is shown to be thermodynamically unstable with respect to decomposition to lead iodide and methylammonium iodide, even in the absence of ambient air or light or heat-induced defects, thus limiting its long-term use in devices. The formation enthalpy from binary halide components becomes less favorable in the order MAPbCl3, MAPbBr3, MAPbI3, with only the chloride having a negative heat of formation. Optimizing the geometric match of constituents as measured by the Goldschmidt tolerance factor provides a potentially quantifiable thermodynamic guide for seeking chemical substitutions to enhance stability.

Perovskites are widely known for their enormous possibility of elemental substitution, which leads to a large variety of physical properties. Hybrid perovskites such as CH3NH3PbI3(MAPbI3) and CH3NH3PbCl3(MAPbCl3) are perovskites with anA[XII]B[VI]X[II]3-structure, whereAis an organic molecule,Bis a lead(II) cation andXis a halide anion of iodine or chlorine. Whereas MAPbCl3crystallizes in the cubic space group Pm{\overline 3}m, MAPbI3is in the tetragonal space groupI4/mcm. The substitution of I by Cl leads to an increased tolerance against humidity but is challenging or even impossible due to their large difference in ionic radii. Here, the influence of an increasing Cl content in the reaction solution on the miscibility of the solid solution members is examined systematically. Powders were synthesized by two different routes depending on the I:Cl ratio. High-resolution synchrotron X-ray data are used to establish values for the limits of the miscibility gap which are 3.1 (1.1) mol% MAPbCl3in MAPI and 1.0 (1) mol% MAPbI3in MAPCl. The establishment of relations between average pseudo-cubic lattice parameters for both phases allows a determination of the degree of substitution from the observed lattice parameters.

The epitaxially fabricated MAPbBr₃/Bi³⁺-doped MAPbCl₃ PSCs pN heterojunction shows advanced X-ray detection performance with decreased dark current density and faster response time under relatively high external reverse voltage.

Perovskite Solar Cells (PSC), with the efficiency of more than 22%, has shown promising prospects for the future of environmentally friendly technology. However, low stability on humidity is a major problem limiting the commercialization of PSC. The perovskite material commonly used as a perovskite solar-cell active material is methylammonium lead tri-iodide (CH3NH3PbI3 or MAPbI3) prepared with a mixture of methylammonium-iodide (MAI) and lead iodide (PbI2). Perovskite material MAPbI3 is hygroscopic and easily decomposed into its constituent material, thereby reducing the performance of the PSC. Meanwhile, perovskite methylammonium lead-bromide (MAPbBr3) has higher moisture stability than MAPbI3 because it has a cubic crystal structure that has high symmetry. However, the efficiency of solar cells using MAPbBr3 as active material is lower than that of MAPbI3, due to a higher bandgap (~2.2 eV) than that of MAPbI3 (~1.5 eV). Therefore the wavelength range of sunlight absorbed by MAPbBr3 is shorter. We have studied the effect of the ratio of Bromium ion (Br-) insertion into MAPbI3 perovskite, forming mixed perovskite halide MAPbBrxI3-x on the stability of thin perovskite films in ambient with air humidity 70%. The value of x is varied from x = 0, 0.25, 0.5, 0.75 and 3. We measured the evolution of UV-Vis spectra and XRD patterns of thin perovskite films. The MAPbBr3 perovskite film is the most stable in high air relative humidity (> 70%). While mixed perovskite films with x = 0.5 are more stable as compared to the other x values based on absorption spectra. The XRD results showed that the stability of mixed halide perovskite is decreased with the increasing of x value.

In situ real-time spectroscopic ellipsometry (RTSE) measurements have been conducted on MAPbI3, MA0.7FA0.3PbI3, and (FAPbI3)0.95(MAPbBr3)0.05 perovskite thin films when exposed to different levels of relative humidity at given temperatures over time. Analysis of RTSE measurements track changes in the complex dielectric function spectra and structure, which indicate variations in stability influenced by the underlying material, preparation method, and perovskite composition. MAPbI3 and MA0.7FA0.3PbI3 films deposited on commercial fluorine-doped tin oxide coated glass are more stable than corresponding films deposited on soda lime glass directly. (FAPbI3)0.95(MAPbBr3)0.05 films on soda lime glass showed improved stability over the other compositions regardless of the substrate, and this is attributed to the preparation method as well as the final composition.

The presented diploma thesis deals with the preparation of perovskite single crystals by inverse thermal crystallization and subsequent study of the basic properties of these hybrid organic-inorganic materials that can be used in various optoelectronic (photodetectors, transistors, lasers, LEDs) or photovoltaic applications. Their behavior in the electric field was studied by impedance spectroscopy. Impedance and capacitance-voltage (C-V) characteristics (frequency dependences) were measured in the dark and in the light. From the impedance dependences for measurements at 0 V voltage in the dark, the equivalent circuit was modeled and its parameters and dielectric constant were determined. From the C-V dependence, Mott-Schottky analysis determined the parameters – "flat-band" potential U_"fb" and charge carrier density N_"C-V" , the parameter – the so-called Warburg coefficient was found, which together with the parameter N_"C-V" was used to calculate the diffusion coefficient D.

This diploma thesis is focused on preparation of perovskite methylammonium lead bromide thin film layers and also thin film layers of its precursors, namely methylammonium bromide and lead(II) bromide, by spin-coating from the solution; and optical characterisation of the prepared thin film layers by UV-VIS spectroscopy and spectroscopical ellipsometry. Methylammonium bromide does not absorb in visible nor ultraviolet region, the maximum absorption of lead(II) bromide occurred in ultraviolet region, methylammonium lead bromide absorbs in visible region. Optical band gaps were determined by Tauc method to (3,5 ± 0,1) eV for lead(II) bromide and 2,15 eV, respectively 2,25 eV for perovskite. Refractive indices and extinction coefficients were determined by ellipsometry in range of wavelengths from 290 nm to 830 nm and their dependence with layer thickness was discussed. Ellipsometry model used in this thesis consist on Tauc-Lorentz oscillators for methylammonium bromide, methylammonium lead bromide and partially for lead(II) bromide, which another part is formed by New Amorphous oscillator.

This thesis is focused on the study of the detection of electromagnetic radiation using monocrystalline perovskites. Theoretical part deals with basic principles of detections and possible applications of hybrid perovskite crystals in the field of ultraviolet and visible spectrum detection. Parameters of the recently published perovskite photodetectors are also presented. Experimental part describes synthesis, structural and optical properties of MAPbBr3 single crystals and electrical characterization of the Au/MAPbBr3/Au photodetector. Photodetector parameters (responsivity, external quantum efficiency and specific detectivity) are calculated based on the spectral and switching (on/off) current responses.

Negli ultimi anni i dispositivi optoelettronici basati su perovskiti ibride ad alogenuri organo-metallici, come celle solari e rivelatori di radiazione, hanno destato un crescente interesse per le loro straordinarie performance. Nonostante questo, molte proprietà fondamentali di questi materiali sono ancora sconosciute e il loro studio è la chiave per l’ottimizzazione dei dispositivi finali. Per realizzare questo lavoro di tesi sono state eseguite misure di fotoluminescenza (PL) su cristalli singoli di tribromuro di metilammonio di piombo (MAPbBr3) a seguito di irradiamento con raggi X, con l’obiettivo di comprendere l’effetto della radiazione sulla struttura elettronica del materiale. In particolare, lo studio dei campioni è finalizzato ad analizzare il comportamento degli eccitoni, la principale sorgente di fotoluminescenza in questi materiali. Si è scelto di eseguire misure di PL per confermare l’ipotesi, nata da misure precedenti di assorbimento in funzione dell’irraggiamento effettuate dal gruppo di ricerca, che l’irraggiamento modifichi l’energia di legame eccitonica nel materiale. I dati risultanti dagli spettri di PL hanno fornito informazioni in accordo con tale ipotesi, rivelandosi uno strumento efficace per analizzare e comprendere le proprietà ottiche di questi materiali.

Les perovskita orgàniques/inorgàniques híbrides han atret molta atenció des que es van introduir per primera vegada en un dispositiu fotovoltaic fa deu anys, obtenint una eficiència de el 3%. Des de llavors, l’eficiència de les cel·les solars de perovskita ha augmentat fins a gairebé igualar l’eficiència de les cel·les fotovoltaiques comercials de silici. A més, permet la fabricació de dispositius flexibles a un preu reduït. A causa de les seves propietats optoelectròniques excepcionalment bones, també s’està duent a terme una intensa recerca per trobar diferents aplicacions d’aquest tipus de materials, ja sigui com a sensors, làsers o díodes emissors de llum. No obstant això, encara s’han d’abordar alguns problemes que presenten, com la inestabilitat química o estructural en condicions ambientals. Per tal de comprendre millor l’estabilitat estructural i el paper exercit per la interacció entre el catió orgànic i la xarxa inorgànica, estudiem les propietats estructurals i optoelectròniques de les perovskita de la família FAxMA1-xPbI3 a diferents pressions (fins a 15 GPa) i temperatures (de 10 a 385 K). La nostra investigació d’aquest material és realitzada per mitjà d’espectroscòpia òptica no invasiva, com fotoluminiscència (PL), Raman i elipsometría. En els articles aquí recopilats es mostra el primer diagrama de fase complet de perovskita de iodur de plom de cations mixtes (formamidinio i metilamonio), en funció de la temperatura i la composició. Aquest diagrama pot servir per avaluar la concentració relativa òptima dels cations orgànics per estabilitzar la fase cúbica pel que fa als canvis de temperatura. Aquests materials també presenten una dependència atípica del bandgap amb temperatura, que en la literatura s’atribueix exclusivament a la renormalització del gap causa de la interacció electró-fonó. No obstant això, és aquest treball mostrem que els efectes d’expansió tèrmica també juguen un paper decisiu en la dependència del gap amb temperatura. De totes les combinacions de la família de perovskita d’halur organometàl·lic, MAPbI3 és probablement el més estudiat a causa de les seves excel·lents propietats. Se sap que la interacció entre el moviment dels cations orgànics i la gàbia inorgànica rígida té un paper decisiu en l’estructura cristal·lina d’aquest material. Per exemple, a causa de el desordre dinàmic de les molècules de metilamonio, la perovskita MAPbI3 adopta una fase cúbica altament simètrica a altes temperatures. Quan es refreda, tant la contracció de la xarxa com la reducció de la simetria a causa d’una transició a una fase ortorrómbica bloquegen les molècules de MA en els buits de la xarxa inorgànica. En els articles aquí compilats observem per primera vegada un efecte similar però a temperatura ambient, aplicant pressió hidrostàtica a el material. En ambdós casos, el bloqueig dels cations de MA es pot observar indirectament a través d’una reducció dràstica dels amples de línia de fonons en els mesuraments Raman. Demostrant, d’aquesta manera, que és possible alterar les propietats vibratòries del material aplicant una pressió controlada. Finalment, la modificació del valor del bandgap i la variació de l’estructura de bandes de sistema mixt FAxMA1-xPbI3 s’avalua en funció de la composició de FA amb elipsometría i fotoluminiscència.
Las perovskitas orgánicas/inorgánicas híbridas han atraído mucha atención desde que se introdujeron por primera vez en un dispositivo fotovoltaico hace diez años, obteniendo una eficiencia de alrededor del 3%. Desde entonces, la eficiencia de las celdas solares de perovskita ha aumentado hasta casi igualar la eficiencia de las celdas fotovoltaicas comerciales de silicio. Además, permite la fabricación de dispositivos flexibles a un precio reducido. Debido a sus propiedades optoelectrónicas excepcionalmente buenas, también se está llevando a cabo una intensa investigación para encontrar diferentes aplicaciones de este tipo de materiales, ya sea como sensores, láseres o diodos emisores de luz. Sin embargo, todavía deben abordarse algunos problemas que presentan, como la inestabilidad química o estructural en condiciones ambientales. Con el fin de comprender mejor la estabilidad estructural y el papel desempeñado por la interacción entre el catión orgánico y la red inorgánica, estudiamos las propiedades estructurales y optoelectrónicas de las perovskitas de la familia FAxMA1-xPbI3 a diferentes presiones (hasta 15 GPa) y temperaturas (de 10 a 385 K). Nuestra investigación de este material es realizada por medio de espectroscopía óptica no invasiva, como fotoluminiscencia (PL), Raman y elipsometría. En los artículos aquí recopilados se muestra el primer diagrama de fase completo de perovskitas de yoduro de plomo de cationes mixtos (formamidinio y metilamonio), en función de la temperatura y la composición. Este diagrama puede servir para evaluar la concentración relativa óptima de los cationes orgánicos para estabilizar la fase cúbica con respecto a los cambios de temperatura. Estos materiales también presentan una dependencia atípica del bandgap con temperatura, que en la literatura se atribuye exclusivamente a la renormalización del gap debido a la interacción electrón-fonón. Sin embargo, es éste trabajo mostramos que los efectos de expansión térmica también juegan un papel decisivo en la dependencia del gap con temperatura. De todas las combinaciones de la familia de perovskitas de haluro organometálico, MAPbI3 es probablemente el más estudiado debido a sus excelentes propiedades. Se sabe que la interacción entre el movimiento de los cationes orgánicos y la jaula inorgánica rígida tiene un papel decisivo en la estructura cristalina de este material. Por ejemplo, debido al desorden dinámico de las moléculas de metilamonio, la perovskita MAPbI3 adopta una fase cúbica altamente simétrica a altas temperaturas. Cuando se enfría, tanto la contracción de la red como la reducción de la simetría debido a una transición a una fase ortorrómbica bloquean las moléculas de MA en los huecos de la red inorgánica. En los artículos aquí compilados observamos por primera vez un efecto similar pero a temperatura ambiente, aplicando presión hidrostática al material. En ambos casos, el bloqueo de los cationes de MA se puede observar indirectamente a través de una reducción drástica de los anchos de línea de fonones en las mediciones Raman. Demostrando, de ésta manera, que es posible alterar las propiedades vibratorias del material aplicando una presión controlada. Finalmente, la modificación del valor del bandgap y la variación de la estructura de bandas del sistema mixto FAxMA1-xPbI3 se evalúa en función de la composición de FA con elipsometría y fotoluminiscencia.
Hybrid organic/inorganic perovskites have attracted a lot of attention since they were first introduced in a working photovoltaic device ten years ago, yielding an efficiency of around 3%. Since then, the efficiency of the perovskite solar cells has risen to almost stand toe to toe with that of commercial silicon photovoltaics. Besides, it allows the fabrication of flexible devices at an inexpensive cost. Due to its exceptionally good optoelectronic properties, there is also an intense research for different applications of this type of materials, such as sensors, lasers or light-emitting diodes. However, they still present some issues that need to be addressed, such as chemical or structural instabilities under ambient conditions. In order to better understand the structural stability, and the role played by the interaction between the organic cation and the inorganic framework, we studied the structural and optoelectronic properties of perovskites of the family FAxMA1-xPbI3 at different pressures (up to 15 GPa) and temperatures (10 to 385 K). We investigated this material by noninvasive optical spectroscopy means, such as photoluminescence (PL), Raman and ellipsometry. In the articles here compiled, the first complete phase diagram of mixed cation (formamidinium and methylammonium) lead iodide perovskites is provided as a function of temperature and composition. This serves to assess the best relative concentration of the organic cations to stabilize the cubic phase with respect to temperature changes. These materials also present an atypical dependence of the bandgap with temperature, which in the literature is ascribed exclusively to a huge electron-phonon renormalization. However, here we show that thermal expansion effects also play a decisive role in the temperature behavior of the fundamental gap. From all the combinations in the family of organometal halide perovskites, MAPbI3 is probably the most studied due to its outstanding optoelectronic properties. It is known that the interplay between the movement of the organic cations and the rigid inorganic cage has a decisive role in the crystalline structure of this material. For instance, due to the dynamic disorder of the methylammonia, MAPbI3 adopts a highly symmetric cubic phase at high temperatures. When cooling down, both the contraction of the lattice and the reduction of symmetry due to a transition to an orthorhombic phase lock the MA molecules in the cage voids. We are able to observe for the first time a similar effect but at room temperature, by applying hydrostatic pressure to the material. In both cases, the locking of the MA cations can be indirectly observed through a drastic reduction of the phonon linewidths in Raman experiments. We have shown, in this way, that it is possible to alter the vibrational properties of the material by applying a controlled hydrostatic pressure. Finally, the tuning of the bandgap and the variation of the band structure of the mixed-system FAxMA1-xPbI3 is evaluated as a function of FA composition with ellipsometry and photoluminescence.

碩士
國立臺北科技大學
光電工程系
106
In this study, MAPbBr3 perovskite quantum dots (QD-MAPbBr3) were prepared by as simple and rapid method.Octylammonium bromide (OABr) makes MAPbBr3 with better exciton binding energy, surface morphology and stability.Moreover,the color of the MAPbBr3 film is dark orange,but it becomes light yellow after OABr used.Therefore MAPbBr3 added with OABr have a better light transmittance.To form a nanocrystalline thin film,QD-MAPbBr3 was coated on NiO or PEDOT:PSS thin films grown on patterned ITO substrates by a spin-coating method in a nitrogen-filled glove box for devices.Subsequently, C60 and Ag were deposited on QD-MAPbBr3 films using a thermal evaporation to fabricate Glass/ITO/NiO/QD-MAPbBr3/C60/Ag perovskite solar cells,where NiO, QD-MAPbBr3, C60 were used as a hole transport layer,active layer and electron transport layer,respectively.To realize material characteristics,x-ray diffraction (XRD),scanning electron microscope (SEM),UV/VIS/NIR spectrometer,and photoluminescence spectrometers (PL) were used to analysis crystallinity,surface morphology,transmittance,and optical behavior of the QD-MAPbBr3 films.The J-V characteristics of devices were evaluated by a solar simulator system.

碩士
國立臺北科技大學
光電工程系
107
This thesis is on metal-semiconductor-metal MAPbBr3 perovskite crystal photodetector. Perovskite crystals are produced by constant temperature growth. To explore the effect of different crystal growth temperature on crystal structure, we analyzed the crystal structure, crystal uniformity, and defects by XRD and PL. We found the best temperature for crystal growth and subsequently fabricated the perovskite crystal into photodetector. The current-to-voltage characteristic curve（IV curve）, optical responsivity, and carrier mobility of the light detector were measured. The electrode of the photodetector is an interdigitated structure in which MAPbBr3 perovskite crystal semiconductor materials are used as a light absorbing layer. On the electrode, C60 is used as an electron transport layer, resulting in a light response exhibited at an incident light wavelength of 400 nm. When the photodetector was biased to 15V, 16V, 17V, 18V, 19V and 20V, the optimal optical responsivity is 13.13 A/W, 14.97 A/W, 17.13 A/W, 19.98 A/W, 22.48 A/W and 24.50 A/W; the carrier mobility was 14.4 cm2V-1s-1.

Abstract Hybrid metal halide perovskite is a promising material for efficient photovoltaic cells and potential thermoelectric energy conversion. This paper investigates phonon thermal transport in iodine-vacancy-defect methylammonium lead iodide (MAPbI3) perovskite using molecular dynamics simulations. The results show that the iodine vacancy defects suppress the thermal conductivity of defective MAPbI3. This effect is enhanced with increasing the defect concentration. The reduction of thermal conductivity of MAPbI3 with iodine vacancy defects compared with the pristine counterpart is mainly attributed to the enhanced phonon anharmonicity and shorter phonon relaxation time due to the phonon-defect scattering. Although iodine diffusion is observed in MAPbI3 with iodine vacancy defects, defect migration has a limited impact on mass-transfer induced convective phonon transport, while it is a source of phonon anharmonicity. This study may provide guidance for theoretical research and industrial application of as-synthesized metal halide perovskites with intrinsic defects.