Periodic Reporting for period 4 - ANHARMONIC (Anharmonic Semiconductors)
Berichtszeitraum: 2024-05-01 bis 2024-10-31
The research funded by the ERC Starting Grant addresses a fundamental problem in materials science: how strongly anharmonic lattice dynamics influence the electronic, optical, and transport properties of functional materials. Traditionally, the behavior of semiconductors, ion conductors, and optoelectronic materials has been understood within the harmonic approximation, where atomic vibrations are treated as independent oscillators. However, many technologically relevant materials, such as halide perovskites, solid-state ion conductors, and organic molecular crystals, exhibit significant anharmonicity that cannot be captured by conventional models. This research aims to understand how anharmonic lattice fluctuations modify material properties, enabling new mechanisms for charge transport, defect passivation, and phase stability.
The importance of this research extends far beyond fundamental science, as it directly impacts key technologies in energy, electronics, and sustainability. In optoelectronics, for example, halide perovskites have revolutionized solar cells and light-emitting devices, yet their remarkable performance remains poorly understood due to their highly anharmonic nature. Understanding the role of dynamic disorder and local polar fluctuations in these materials can lead to more efficient, stable, and scalable perovskite-based technologies. Similarly, in energy storage, solid-state ion conductors are essential for next-generation batteries, where fast ionic transport is critical for high-performance electrolytes. This research provides insights into how lattice dynamics facilitate or hinder ion mobility, guiding the design of better solid-state battery materials. Furthermore, in organic molecular crystals, understanding vibrational couplings can improve material stability and electronic properties, influencing applications from flexible electronics to pharmaceutical formulations.
The overall objectives of the project are threefold. First, it aims to develop advanced experimental techniques, particularly time-resolved Raman spectroscopy, to probe anharmonic lattice dynamics with unprecedented precision. This approach allows direct observation of non-equilibrium lattice effects, polaron formation, and self-trapped excitons in real time. Second, the research seeks to establish a theoretical framework that links anharmonic lattice behavior to macroscopic material properties, integrating experimental findings with first-principles calculations and molecular dynamics simulations. Finally, the project aims to apply these insights to improve the performance and stability of real-world materials, guiding the rational design of new semiconductors, solid electrolytes, and molecular crystals with enhanced functionalities. By bridging fundamental physics with technological applications, this research contributes to the broader goal of designing materials for a sustainable and energy-efficient future.
The importance of this research extends far beyond fundamental science, as it directly impacts key technologies in energy, electronics, and sustainability. In optoelectronics, for example, halide perovskites have revolutionized solar cells and light-emitting devices, yet their remarkable performance remains poorly understood due to their highly anharmonic nature. Understanding the role of dynamic disorder and local polar fluctuations in these materials can lead to more efficient, stable, and scalable perovskite-based technologies. Similarly, in energy storage, solid-state ion conductors are essential for next-generation batteries, where fast ionic transport is critical for high-performance electrolytes. This research provides insights into how lattice dynamics facilitate or hinder ion mobility, guiding the design of better solid-state battery materials. Furthermore, in organic molecular crystals, understanding vibrational couplings can improve material stability and electronic properties, influencing applications from flexible electronics to pharmaceutical formulations.
The overall objectives of the project are threefold. First, it aims to develop advanced experimental techniques, particularly time-resolved Raman spectroscopy, to probe anharmonic lattice dynamics with unprecedented precision. This approach allows direct observation of non-equilibrium lattice effects, polaron formation, and self-trapped excitons in real time. Second, the research seeks to establish a theoretical framework that links anharmonic lattice behavior to macroscopic material properties, integrating experimental findings with first-principles calculations and molecular dynamics simulations. Finally, the project aims to apply these insights to improve the performance and stability of real-world materials, guiding the rational design of new semiconductors, solid electrolytes, and molecular crystals with enhanced functionalities. By bridging fundamental physics with technological applications, this research contributes to the broader goal of designing materials for a sustainable and energy-efficient future.
From the beginning of the project, the research has focused on understanding the role of anharmonic lattice dynamics in determining the properties of functional materials, with a particular emphasis on halide perovskites, solid-state ion conductors, and organic molecular crystals. The work has been structured around three key objectives: developing advanced experimental techniques to probe anharmonic lattice dynamics, establishing theoretical models linking anharmonic behavior to macroscopic material properties, and applying these insights to improve the stability and performance of technologically relevant materials.
One of the major accomplishments has been the development and implementation of time-resolved spontaneous Raman spectroscopy using time-correlated single-photon counting (TCSPC). This technique enabled direct observation of non-equilibrium lattice dynamics with picosecond precision, allowing us to track polaron formation, self-trapped excitons, and lattice relaxation processes in real time.
For organic molecular crystals, the work uncovered a previously unrecognized form of vibrational coupling that affects phase stability and charge transport. Our results showed that anharmonic fluctuations contribute to polymorphism and may influence non-monotonic relaxation dynamics, affecting the thermodynamic stability of different crystal phases. These insights have broad implications for applications ranging from flexible electronics to pharmaceuticals.
The dissemination and exploitation of these results have been a key priority. The research has led to multiple high-impact publications, including studies in Physical Review Materials, Advanced Materials, and ACS Nano. These findings have been presented at international conferences, including the Materials Research Society (MRS), European Materials Research Society (E-MRS), and the American Physical Society (APS) March Meeting, fostering discussions on how anharmonicity impacts material functionality. The methodologies developed in this project are now being adopted by other research groups, particularly in the study of next-generation semiconductors and solid-state batteries.
From an application perspective, these insights provide guidelines for designing more stable and efficient optoelectronic materials, better solid electrolytes for batteries, and improved molecular crystals for organic electronics. Collaborations with industry partners and experimental groups have begun to explore how these findings can be translated into practical material design strategies.
One of the major accomplishments has been the development and implementation of time-resolved spontaneous Raman spectroscopy using time-correlated single-photon counting (TCSPC). This technique enabled direct observation of non-equilibrium lattice dynamics with picosecond precision, allowing us to track polaron formation, self-trapped excitons, and lattice relaxation processes in real time.
For organic molecular crystals, the work uncovered a previously unrecognized form of vibrational coupling that affects phase stability and charge transport. Our results showed that anharmonic fluctuations contribute to polymorphism and may influence non-monotonic relaxation dynamics, affecting the thermodynamic stability of different crystal phases. These insights have broad implications for applications ranging from flexible electronics to pharmaceuticals.
The dissemination and exploitation of these results have been a key priority. The research has led to multiple high-impact publications, including studies in Physical Review Materials, Advanced Materials, and ACS Nano. These findings have been presented at international conferences, including the Materials Research Society (MRS), European Materials Research Society (E-MRS), and the American Physical Society (APS) March Meeting, fostering discussions on how anharmonicity impacts material functionality. The methodologies developed in this project are now being adopted by other research groups, particularly in the study of next-generation semiconductors and solid-state batteries.
From an application perspective, these insights provide guidelines for designing more stable and efficient optoelectronic materials, better solid electrolytes for batteries, and improved molecular crystals for organic electronics. Collaborations with industry partners and experimental groups have begun to explore how these findings can be translated into practical material design strategies.
The Anharmonic project has significantly advanced the understanding of anharmonic lattice dynamics in functional materials, surpassing the current state of the art in several key areas. By developing innovative experimental techniques and theoretical models, the project has provided new insights into how anharmonicity influences material properties, leading to potential applications in energy, electronics, and materials science.
Progress beyond the state of the art includes several major advancements. The project introduced time-resolved spontaneous Raman spectroscopy using time-correlated single-photon counting (TCSPC), enabling direct observation of non-equilibrium lattice dynamics with picosecond precision. This advancement allows for real-time tracking of phenomena such as polaron formation and lattice relaxation processes, which were previously challenging to monitor.
A coarse-grained theoretical model was developed to unify existing theories of light scattering in perovskites, addressing discrepancies between classical phonon-based models and observed liquid-like Raman responses. This model provides a comprehensive framework for understanding the impact of anharmonic lattice vibrations on material properties.
The project also uncovered previously unrecognized vibrational couplings in organic molecular crystals, showing that anharmonic fluctuations contribute to polymorphism and influence the thermodynamic stability of different crystal phases. These insights have implications for the development of flexible electronics and pharmaceuticals.
Progress beyond the state of the art includes several major advancements. The project introduced time-resolved spontaneous Raman spectroscopy using time-correlated single-photon counting (TCSPC), enabling direct observation of non-equilibrium lattice dynamics with picosecond precision. This advancement allows for real-time tracking of phenomena such as polaron formation and lattice relaxation processes, which were previously challenging to monitor.
A coarse-grained theoretical model was developed to unify existing theories of light scattering in perovskites, addressing discrepancies between classical phonon-based models and observed liquid-like Raman responses. This model provides a comprehensive framework for understanding the impact of anharmonic lattice vibrations on material properties.
The project also uncovered previously unrecognized vibrational couplings in organic molecular crystals, showing that anharmonic fluctuations contribute to polymorphism and influence the thermodynamic stability of different crystal phases. These insights have implications for the development of flexible electronics and pharmaceuticals.