Periodic Reporting for period 1 - SpinSC (Spin-mediated spectral conversion for efficient photovoltaics)
Reporting period: 2023-03-01 to 2025-02-28
To tackle the global energy crisis and achieve carbon neutrality, we must change the way we produce and use energy. Solar energy and battery technologies are at the heart of this transformation. Solar energy is projected to become Europe's on of the main sources of electricity by 2050. Improving the performance of solar technologies is essential to meet this demand sustainably and cost-effectively. However, even the most advanced commercial solar cells are rapidly approaching their theoretical efficiency limits. To go further, we need technologies that can harvest sunlight more effectively by overcoming the physical limitations of today’s photovoltaic devices.
One promising solution is to make better use of sunlight by using the energy of the photons that are typically lost via transmission and heat in single junction solar cells. Spectral conversion (SC) is one of the approaches to achieve this solution. Through SC, light that would otherwise be wasted is transformed into energy the solar cell can use, via a spectral conversion layer typically placed at the bottom or at the top of the cell. This project, SpinSC, focused on understanding and optimising the underlying electronic processes that make spectral conversion possible, aiming to increase solar cell efficiency in a way that complements existing technologies.
Two advanced light conversion mechanisms—singlet fission and triplet–triplet annihilation—are central to this approach. These processes are governed by the behaviour of electrons and their spin, a fundamental quantum property. Unfortunately, the spin interactions involved in these conversions are complex and short-lived, making them difficult to control and study with traditional methods. SpinSC tackled this challenge by combining state-of-the-art simulation techniques with experimental insight to explore and control the spin dynamics driving spectral conversion.
The project was hosted at the University of Padua and in collaboration with the University of New South Wales in Sydney, leveraging their interdisciplinary expertise that bridges quantum physics, materials science, and photovoltaics. SpinSc aimed to answer fundamental questions: How do molecular structure and movement influence spin-based energy conversion? What role do interactions with atomic nuclei play in these processes? And how can we use light itself to induced molecular reorganisation and spin states conversion in ways that boost efficiency?
The ultimate objective if this project was not just to explain how spin-mediated spectral conversion works, but to create practical design rules that can be used to build more efficient solar devices. If successful, these findings could lead to new materials for organic solar cells, potentially exceeding 45% efficiency when combined with existing technologies.
One promising solution is to make better use of sunlight by using the energy of the photons that are typically lost via transmission and heat in single junction solar cells. Spectral conversion (SC) is one of the approaches to achieve this solution. Through SC, light that would otherwise be wasted is transformed into energy the solar cell can use, via a spectral conversion layer typically placed at the bottom or at the top of the cell. This project, SpinSC, focused on understanding and optimising the underlying electronic processes that make spectral conversion possible, aiming to increase solar cell efficiency in a way that complements existing technologies.
Two advanced light conversion mechanisms—singlet fission and triplet–triplet annihilation—are central to this approach. These processes are governed by the behaviour of electrons and their spin, a fundamental quantum property. Unfortunately, the spin interactions involved in these conversions are complex and short-lived, making them difficult to control and study with traditional methods. SpinSC tackled this challenge by combining state-of-the-art simulation techniques with experimental insight to explore and control the spin dynamics driving spectral conversion.
The project was hosted at the University of Padua and in collaboration with the University of New South Wales in Sydney, leveraging their interdisciplinary expertise that bridges quantum physics, materials science, and photovoltaics. SpinSc aimed to answer fundamental questions: How do molecular structure and movement influence spin-based energy conversion? What role do interactions with atomic nuclei play in these processes? And how can we use light itself to induced molecular reorganisation and spin states conversion in ways that boost efficiency?
The ultimate objective if this project was not just to explain how spin-mediated spectral conversion works, but to create practical design rules that can be used to build more efficient solar devices. If successful, these findings could lead to new materials for organic solar cells, potentially exceeding 45% efficiency when combined with existing technologies.
SpinSC set out to investigate how to optimise spectral conversion in organic molecules. Over the course of the project, a comprehensive theoretical and computational framework was developed to study two key spectral conversion processes: singlet fission (SF) and triplet–triplet annihilation (TTA). To this end, we have used state-of-the-art quantum simulation methods. The first phase focused on modelling how molecular reorganisation—essentially how molecules bend and move—affect the spin states that drive SF and TTA. This study revealed how the flexibility of a material influences its ability perform spectral conversion efficiently, showing how "floppy" molecules open to better conversion. These insights lay the groundwork for selecting and designing materials with optimal structural properties.
The second phase of the project explored the efficiency of spectral conversion in large aggregates of molecules, such as rings of molecules or polymers. To carry out this work, we used advanced tensor network methods, a technique that is opens to the efficient simulation of the dynamics of large systems even at the level of their fundamental interactions. Thanks to these innovative tools, the project achieved the optimisation of singlet fission in large rings with more than 100 molecules. We now understand the conditons to promote the formation of triplet pair states, which can be used to produce two charge carriers for each absorbed photon.
The second phase of the project explored the efficiency of spectral conversion in large aggregates of molecules, such as rings of molecules or polymers. To carry out this work, we used advanced tensor network methods, a technique that is opens to the efficient simulation of the dynamics of large systems even at the level of their fundamental interactions. Thanks to these innovative tools, the project achieved the optimisation of singlet fission in large rings with more than 100 molecules. We now understand the conditons to promote the formation of triplet pair states, which can be used to produce two charge carriers for each absorbed photon.
SpinSC delivered several key breakthroughs in our understanding and control of spin-mediated spectral conversion—an emerging approach to boosting solar energy efficiency. The project pushed the frontiers of quantum modelling, identifying new strategies to guide the development of materials capable of turning sunlight into electricity more effectively than current technologies allow.
One of the major results was the creation of a theoretical framework linking molecular motion to spin conversion efficiency. SpinSC demonstrated how the conformational dynamics of molecules—how they bend, twist, and shift—play a crucial role in determining whether energy-carrying excitons can be split or merged efficiently through singlet fission or triplet–triplet annihilation. This insight enables material scientists to tune molecular structures with greater precision to favour desired conversion pathways.
SpinSC also introduced a versatile model and power simulation method to optimise the design of molecular aggregates for spectral conversion in organic materials. This approach is based on the simulation of excited state dynamics using tensor network methods, and was used to obtain the first spectral conversion guidelines using non-perturbative methods for up to 128 molecules.
All software developed during the project was designed to be modular, scalable, and openly shared with the research community. These tools can now be used to screen new candidate materials, simulate experimental conditions, and design photonics structures tailored to specific spin behaviours.
One of the major results was the creation of a theoretical framework linking molecular motion to spin conversion efficiency. SpinSC demonstrated how the conformational dynamics of molecules—how they bend, twist, and shift—play a crucial role in determining whether energy-carrying excitons can be split or merged efficiently through singlet fission or triplet–triplet annihilation. This insight enables material scientists to tune molecular structures with greater precision to favour desired conversion pathways.
SpinSC also introduced a versatile model and power simulation method to optimise the design of molecular aggregates for spectral conversion in organic materials. This approach is based on the simulation of excited state dynamics using tensor network methods, and was used to obtain the first spectral conversion guidelines using non-perturbative methods for up to 128 molecules.
All software developed during the project was designed to be modular, scalable, and openly shared with the research community. These tools can now be used to screen new candidate materials, simulate experimental conditions, and design photonics structures tailored to specific spin behaviours.