Publication

Magnetic Resonance and Hyperpolarization Methods for Perovskite Photovoltaics

Aditya Mishra
2022
EPFL thesis
Abstract

Solid-state NMR can provide information about the atomic-level microstructure and dynamics in materials as it directly probes the local nuclear environment. In the last decade, halide perovskites have drawn intense interest because of their intriguing optoelectronic properties making them suitable for solar cells, LEDs, and photodetectors. Meanwhile, perovskite solar cells already achieve power conversion efficiencies over 25%, but they are also unstable and degrade under operating conditions. The community has developed various strategies to minimize these detrimental effects, however, it is challenging to determine the atomic level structure using conventional techniques. In contrast, solid-state NMR can provide information about structure at the atomic level. NMR applications are often limited by the inherently low sensitivity arising from low concentration, low gyromagnetic ratio, and/or low natural abundance of the NMR active nuclei. In particular, the low mass of thin films limits the usage of NMR for technologically relevant samples. Dynamic nuclear polarization (DNP) is a method to acquire NMR spectra with higher sensitivity, however, it has had limited success for halide perovskites. The objective of this thesis is to develop and apply solid-state NMR and DNP methods to investigate perovskite materials. This thesis contains three sections: In the first section, a few examples of the application of solid-state NMR to halide perovskite systems are presented. Firstly, an NMR crystallography-based approach was developed to determine the supramolecular structure of layered hybrid perovskites with a mixture of two spacer cations. The observed nano-scale phase segregation was proposed to be responsible for providing high efficiency and operational stability. Secondly, using conventional solid-state NMR, the incorporation of the dimethylammonium ion was examined under various conditions. Unusually, solution processed samples were found to have a different metastable structure than mechanosynthesised samples. Finally, the NMR-derived atomic-level structure in current state-of-the-art hybrid and inorganic perovskites is presented. Notably, structural hypotheses were thoroughly investigated using mechanosynthesised perovskites and solution-processed thin films. These structural insights have guided the studies to achieve unprecedented solar cell performance. In the second section, a protocol is developed to investigate cation dynamics in single and multi-cation perovskite systems. This protocol employs quadrupolar relaxometry at high field under magic angle spinning, combined with a rotational diffusion model, to provide the rate of rotation about each principal axis of the cation. The dynamics were found to depend upon the symmetry of the inorganic lattice, but were insensitive to cation alloying. In the third section, a DNP based method is developed enabling the structure to be determined for the surface layer of a single perovskite thin-film. Fast relaxation was found to be the major impediment in DNP performance, but can be partially mitigated by optimal deuteration, resulting in enhancement factors approaching 100. Applying this DNP strategy at 21 T with a 0.7 mm outer diameter rotor, the surface layer structure of a single thin-film was identified. The work presented in this thesis will further open doors to develop and apply NMR methods to this family of optoelectronic materials.

About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Related concepts (32)
Nuclear magnetic resonance
Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field (in the near field) and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance, when the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on the strength of the static magnetic field, the chemical environment, and the magnetic properties of the isotope involved; in practical applications with static magnetic fields up to ca.
Perovskite solar cell
A perovskite solar cell (PSC) is a type of solar cell that includes a perovskite-structured compound, most commonly a hybrid organic–inorganic lead or tin halide-based material as the light-harvesting active layer. Perovskite materials, such as methylammonium lead halides and all-inorganic cesium lead halide, are cheap to produce and simple to manufacture. Solar-cell efficiencies of laboratory-scale devices using these materials have increased from 3.8% in 2009 to 25.
Nuclear magnetic resonance spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. This spectroscopy is based on the measurement of absorption of electromagnetic radiations in the radio frequency region from roughly 4 to 900 MHz. Absorption of radio waves in the presence of magnetic field is accompanied by a special type of nuclear transition, and for this reason, such type of spectroscopy is known as Nuclear Magnetic Resonance Spectroscopy.
Show more
Related publications (75)

Vapor Deposition of Perovskite Solar Cells

Quentin Jean-Marie Armand Guesnay

Thanks to the continuous improvement of crystalline silicon (c-Si) solar cells, largely dominating the market, photovoltaic electricity is nowadays the cheapest source of energy on the market. Yet, solar energy is far from being completely harvested, as t ...
EPFL2023

NMR Crystallography in the Big Data Era: New Methods and Applications Powered by Machine Learning

Manuel Cordova

Structure determination of materials is key to understanding their physical properties. While single-crystal X-ray diffraction is the gold standard for structures displaying long-range order, many materials of interest are polycrystalline and/or disordered ...
EPFL2023

Dynamic Nuclear Polarization of Inorganic Halide Perovskites

David Lyndon Emsley, Michael Allan Hope, Dominik Józef Kubicki, Gabriele Stevanato, Aditya Mishra

The intrinsic low sensitivity of nuclear magnetic resonance (NMR) experiments limits their utility for structure determination of materials. Dynamic nuclear polarization (DNP) under magic angle spinning (MAS) has shown tremendous potential to overcome this ...
2023
Show more
Related MOOCs (9)
Basic Steps in Magnetic Resonance
A MOOC to discover basic concepts and a wide range of intriguing applications of magnetic resonance to physics, chemistry, and biology
Fundamentals of Biomedical Imaging: Magnetic Resonance Imaging (MRI)
Learn about magnetic resonance, from the physical principles of Nuclear Magnetic Resonance (NMR) to the basic concepts of image reconstruction (MRI).
Fundamentals of Biomedical Imaging: Magnetic Resonance Imaging (MRI)
Learn about magnetic resonance, from the physical principles of Nuclear Magnetic Resonance (NMR) to the basic concepts of image reconstruction (MRI).
Show more