Hybrid solar cells based on perovskite

Orientador: Ana Flávia NogueiraDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de QuímicaResumo: As células solares baseadas em perovskita alcançaram eficiência de 20 % em menos de uma década de estudos, tornando-se atraentes à utilização comercial, devido ao seu baixo custo e métodos simples de preparação. Entretanto, muitos fatores que influenciam na formação e propriedades da perovskita ainda precisam de melhor entendimento, sendo essenciais para aumentar ainda mais sua eficiência e estabilidade. Desta forma, a formação da perovskita MAPbI3 pelo método de troca intramolecular foi estudado na primeira parte deste trabalho. Foi demonstrado que a formação da perovskita por este método ocorre através da formação de um intermediário, MA2Pb3I8.2DMSO, quando a amostra não tem contato com o ar do ambiente durante a preparação, que é convertido a perovskita por tratamento térmico. Porém, quando este contato acontece, ocorre a formação direta da perovskita. Assim, foi possível propor um mecanismo de formação com a participação da H2O do ambiente. Na segunda parte foi estudado o efeito do tempo de tratamento térmico dos filmes de perovskita. Com menor tempo de tratamento térmico, o excesso de iodeto de metilamônio não é totalmente eliminado, levando à formação de defeitos que prejudicam a eficiência das células solares. Aumentando o tempo de tratamento térmico este efeito é reduzido e evidenciado pela diminuição da histerese e aumento da eficiência das células solares. Com tratamento térmico de 90 minutos foi possível preparar células solares com eficiência média de 11,00 % na medida inversa, e 10,25 % na medida direta. Após a estabilização a eficiência atingiu 12,89 %. Assim, foi possível demonstrar que a H2O do ambiente e que o tempo de tratamento térmico são fatores que influenciam de maneira decisiva na formação de perovskita sem fase secundária de PbI2 e, consequentemente, na obtenção de células solares com boa eficiênciaAbstract: Perovskite-based solar cells efficiency have reached 20 % in less than a decade of research, becoming commercially attractive due to their low-costs and simple preparation methods. However, many factors that influence perovskite formation and properties are yet to be better understood, and controlling these factors is fundamental to its continuing improvement and stability. Thus, MAPbI3 perovskite formation by intramolecular exchange method was studied as the first part of this work. It was demonstrated that the perovskite formation by this method happened through the formation one intermediate, MA2Pb3I8.2DMSO, when the sample was not exposed to atmosphere during the preparation, which is converted to perovskite by annealing process. Nonetheless, when atmosphere contact occurs, perovskite formation undergoes straightforward. In this way, it was possible to propose a mechanism of formation with the participation of ambient H2O. In the second part, a study of the effect of annealing time of the perovskite films was performed. With short annealing time, the excess of methylammonium iodide is not completely eliminated, leading to the formation of defects that decreases the efficiency of the solar cells. With increasing annealing time, this effect is minimized and evidenced by reduction of the hysteresis and improvement efficiency of solar cells. With 90 minutes of annealing time, it was possible prepare solar cells with average efficiency of 11,00 % in inverse, and 10,25 % in forward measurement. After stabilization, the efficiency reached 12,89 %. Thereby, it was possible to demonstrate that the ambient H2O and annealing time are factors that influence decisively in the perovskite formation without secondary PbI2 phase and, consequently, in obtaining solar cells with good efficiencyMestradoQuimica InorganicaMestre em Química131030/2014-02014/13666-0CNPQFAPES

CÉLULAS SOLARES DE PEROVSKITAS: UMA NOVA TECNOLOGIA EMERGENTE

Solar energy has been considered as an important source of clean and safe energy to overcome the problems associate to the burn of fossil fuels (e.g. climate changes, pollution, health problems, etc.). In the area of photovoltaics, devices that convert solar energy into electricity, perovskites solar cells (PSC) have attracted great attention due to their rapid development, high energy conversion efficiency, diversification of the processing methods and different materials. The fantastic properties of the hybrid perovskite materials, such as high absorption coefficient, direct and tunable bandgap, ambipolar charge carrier, simple preparation, etc., have quoted this technology as one the most important in this century. The rapid development of PSC has provided a significant increase in energy conversion efficiency, which was first reported, in 2009, as 3.8% and now reaches up to 22.10%, according to the National Laboratory of Renewable Energy (NREL). Many studies have been carried out to further increase the efficiency of devices and solve problems as the instability of the material, and the presence of lead, so that the PSC can be applied commercially. This paper presents a review on PSC and the major advances reported in device’s architecture, preparation methods, novel materials and interface engineering

PEROVSKITES SOLAR CELLS: A NEW EMERGING TECHNOLOGY

<p></p><p>Solar energy has been considered as an important source of clean and safe energy to overcome the problems associate to the burn of fossil fuels (e.g. climate changes, pollution, health problems, etc.). In the area of photovoltaics, devices that convert solar energy into electricity, perovskites solar cells (PSC) have attracted great attention due to their rapid development, high energy conversion efficiency, diversification of the processing methods and different materials. The fantastic properties of the hybrid perovskite materials, such as high absorption coefficient, direct and tunable bandgap, ambipolar charge carrier, simple preparation, etc., have quoted this technology as one the most important in this century. The rapid development of PSC has provided a significant increase in energy conversion efficiency, which was first reported, in 2009, as 3.8% and now reaches up to 22.10%, according to the National Laboratory of Renewable Energy (NREL). Many studies have been carried out to further increase the efficiency of devices and solve problems as the instability of the material, and the presence of lead, so that the PSC can be applied commercially. This paper presents a review on PSC and the major advances reported in device’s architecture, preparation methods, novel materials and interface engineering.</p><p></p

X-ray dose effects and strategies to mitigate beam damage in metal halide perovskites under high brilliance X-ray photon source

Metal halide perovskites are versatile photovoltaic and optoelectronic materials. However, they suffer from photo-structural-chemical instabilities whose intricacy requires state-of-the-art tools to investigate their properties and behavior under various conditions. In most cases, those tools strongly interact with the materials leading to undesirable transformations. This study addresses the damage caused by highly intense focused X-ray beams on hybrid organic-inorganic metal halide perovskites through a correlative multi-technique approach. Our results reveal that the damage after irradiation in the ((Cs, FAMA)Pb(Br, I)3) compound is prominent on iodine and organic components at the film surface, reducing their relative quantity. The sample morphology modifies with the formation of an excavated area, whose altered local optical properties indicate the formation of an optically inactive metal layer covering the surface. Interestingly, the bulk remains unaltered with the initial ion proportion demonstrated by the stable photoluminescence emission energy. Controlling the X-ray beam dose and environment - air, nitrogen, and cryogenic conditions - serves as a strategy to mitigate the dose harm. Hence, we combined a controlled X-ray dose with an inert N2 atmosphere to certify the conditions to probe metal halide perovskite properties while mitigating damage efficiently. Finally, we applied optimized conditions to investigate a perovskite compound using X-ray ptychography, reaching a 14-nm spatial resolution, an outcome that has never been attained so far

Revealing the Perovskite Film Formation Using the Gas Quenching Method by In Situ GIWAXS: Morphology, Properties, and Device Performance

The optoelectronic properties, morphology, and consequently the performance of metal halide perovskite solar cells are directly related to the crystalline phases and intermediates formed during film preparation. The gas quenching method is compatible with large-area deposition, but an understanding of how this method influences these properties and performance is scarce in the literature. Here, in situ grazing incidence wide angle X-ray scattering is employed during spin coating deposition to gain insights on the formation of MAPbI(3)and Cs(x)FA(1-)(x)Pb(I0.83Br0.17)(3)perovskites, comparing the use of dimethyl sulfoxide (DMSO) and 2-methyl-n-pyrrolidone (NMP) as coordinative solvents. Intermediates formed using DMSO depend on the perovskite composition (e.g., Cs content), while for NMP the same intermediate [PbI2(NMP)] is formed independently on the composition. For MAPbI(3)and Cs(x)FA(1-)(x)Pb(I0.83Br0.17)(3)with a small amount of Cs (10% and 20%), the best efficiencies are achieved using NMP, while the use of DMSO is preferred for higher (30% and 40%) amount of Cs. The inhibition of the 2H/4H hexagonal phase when using NMP is crucial for the final performance. These findings provide a deep understanding about the formation mechanism in multication perovskites and assist the community to choose the best solvent for the desired perovskite composition aiming to perovskite-on-silicon tandem solar cells

Exploring the formation of formamidinium-based hybrid perovskites by antisolvent methods : in situ GIWAXS measurements during spin coating

Antisolvent methods – solvent engineering and a Lewis base adduct approach – are the most used methods to prepare highly efficient perovskite solar cells (PSCs). These two methods differ only by the ratio between the perovskite (PVSK) and dimethyl sulfoxide (DMSO). In this study, the difference between these two methods and the effect of relative humidity (rH) on the crystallization process were evaluated by in situ Grazing-Incidence Wide Angle X-ray Scattering (in situ GIWAXS) using synchrotron radiation. The technique was applied to the first stages of formation of formamidinium-based perovskite films, under real preparation conditions of spin coating, and at different humidity conditions and time windows to inject the antisolvent. The higher amount of DMSO in the solvent engineering method prolongs the duration of the colloidal gel, which extends the time window for antisolvent injection and, as a consequence, facilitates obtaining films with a homogeneous morphology. Our results confirm that the formation of a cesium/formamidinium-based perovskite takes place through the conversion of 2H–4H hexagonal polytypes directly to a black perovskite without thermal annealing, independent of the rH or method employed. In contrast, a cesium-free, methylammonium/formamidinium-based perovskite follows the 2H–4H–6H polytype sequence. Interestingly, at higher amounts of DMSO and rH (40%), a pure iodide intermediate (MA2Pb3I8·2DMSO) is formed in the cesium-free perovskite, which is undesirable in mixed halide perovskites. Our findings shed new light on the complexity of PVSK film formation, by identifying all crystalline phases in the process, and give clues to manage the composition and environment during film processing, and thus have an impact on efficiency optimization and solar cell manufacturing3922872297CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão tem2017/12582-5; 2017/11986-5The authors thank the LNLS for providing beamtime at the XRD2. R. S. thanks the São Paulo Research Foundation (FAPESP, Grant 2017/12582-5). A. F. N. gratefully acknowledges the support from the FAPESP (Grant 2017/11986-5) and Shell and the strategic importance of the support given by ANP (Brazil's National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation. A. F. N. also acknowledges the CNPq and INE

In situ 2D perovskite formation and the impact of the 2D/3D structures on performance and stability of perovskite solar cells

Hybrid organic and inorganic perovskite solar cells lack long‐term stability, and this negatively impacts the widespread application of this emerging and promising photovoltaic technology. Herein, aiming to increase the stability of perovskite films based on CH3NH3PbI3 and to deeply understand the formation of 2D structures, solutions of alkylammonium chlorides containing 8, 10, and 12 carbons are introduced during the spin‐coating on the surface of 3D perovskite films leading to the in situ formation of 2D structures. It is possible to identify the chemical formulae of some 2D structures formed by X‐ray diffraction and UV–vis analysis of the modified films. Interestingly, the increase in the stability of the CH3NH3PbI3 films due to the formation of a 2D + 3D perovskite network is only possible in planar TiO2 substrates. The increase in stability of the CH3NH3PbI3 films follows the surfactant molecule order: octylammonium (8C) > decylammonium (1 °C) > dodecylammonium (12C) chlorides > standard. An increase of 17.6% in the lifetime of the devices assembled with octylammonium‐modified perovskite film is observed compared with that of the standard device, which is directly linked to the improvement of the charge carrier lifetimes obtained from time‐correlated single photon counting measurements39Perovskite solar cells and optoelectronics. Part 1CAPES - Coordenação de Aperfeiçoamento de Pessoal e Nível SuperiorCNPQ - Conselho Nacional de Desenvolvimento Científico e TecnológicoFAPESP – Fundação de Amparo à Pesquisa Do Estado De São PauloNão temNão tem2017/12582-5; 2013/16245-2; 2017/11986-

Tuning Phase Purity in Chiral 2D Perovskites

Abstract: The introduction of chiral organic spacers in low‐dimensional metal‐halide perovskites triggers chiroptical activity, which is appealing for spintronic applications. However, a comprehensive understanding of structure formation and the ability to control phase purity in such materials have yet to be developed. Herein, the impact of processing conditions on the phase purity, microstructure, and chiroptical properties of chiral 2D perovskites is explored. The anisotropic emergence of a 1D perovskite inside the 2D matrix and its dependence on the organic cation chirality, solvent, and thermal annealing conditions are shown. By controlling these parameters, the in‐plane conductivity of the films is nearly doubled. Furthermore, it is demonstrated, for the first time, that solvent choice and the spatial configuration of the organic cation can have an impact on the residual lattice strain and the energetic disorder of the system. The fundamentals presented here can help to improve the film deposition methods for low‐dimensional chiral perovskites, offering strategies to control phase purity

Postpassivation of multication perovskite with rubidium butyrate

Many multication perovskites for highly stable and efficient solar cells benefit from rubidium iodide introduced in the precursor solution. It is well-known that Rb+ influences positively the optoelectronic and mobility properties and has a direct effect upon crystallization and halide homogenization. As Rb+ is often incorporated by adding RbI in the precursor solution, it can be difficult to distinguish the influence of Rb+ and I– separately. Herein, we report a postpassivation of methylammonium-free (CsFA) perovskite films with rubidium butyrate (RbBu). The passivation with RbBu increases the hydrophobicity of the perovskite surface and passivates shallow and deep traps, leading to an increase of charge-carrier lifetimes and diffusion lengths. Consequently, a better photovoltaic performance is also observed. These superior properties are attributed to both surface (halide-vacancy) and grain-boundary passivation by the carboxylate group and Rb+, respectively. We found that Rb+ itself acts as a direct and powerful passivating agent for multication perovskites, and this is proven by decoupling its contribution and halide’s contribution to other important performance parameters (e.g., crystallization, halide vacancies filling, etc.).</p

Postpassivation of Multication Perovskite with Rubidium Butyrate

Many multication perovskites for highly stable and efficient solar cells benefit from rubidium iodide introduced in the precursor solution. It is well-known that Rb+ influences positively the optoelectronic and mobility properties and has a direct effect upon crystallization and halide homogenization. As Rb+ is often incorporated by adding Rb+ in the precursor solution, it can be difficult to distinguish the influence of Rb+ and I- separately. Herein, we report a postpassivation of methylammonium-free (CsFA) perovskite films with rubidium butyrate (RbBu). The passivation with RbBu increases the hydrophobicity of the perovskite surface and passivates shallow and deep traps, leading to an increase of charge-carrier lifetimes and diffusion lengths. Consequently, a better photovoltaic performance is also observed. These superior properties are attributed to both surface (halide-vacancy) and grain-boundary passivation by the carboxylate group and Rb+, respectively. We found that Rb+ itself acts as a direct and powerful passivating agent for multication perovskites, and this is proven by decoupling its contribution and halide's contribution to other important performance parameters (e.g., crystallization, halide vacancies filling, etc.)