Periodic Reporting for period 2 - FENCES (Ferroelectric Nanocomposites for Enhanced Solar Energy Efficiency)
Periodo di rendicontazione: 2022-12-01 al 2024-05-31
Making use of solar energy efficiently is critical to achieve Net Zero goals while simultaneously meeting ever increasing global energy demands. The main current technology utilised are solar photovoltaics (PVs), mostly based on silicon, which can convert around 25% of incident sunlight into electrical power. There are new PV technologies and materials being developed, but all are based on semiconductor junctions, and are therefore limited to a maximum theoretical efficiency of around 34% for any single junction. At the same time, to address intermittency issues with solar energy, and also provide low-cost, renewable fuel replacements, exciting routes to produce hydrogen or hydrocarbons directly from sunlight and water or CO2 are being developed using photocatalytic solar fuel generation. However, large advances are needed to make this technology viable, and it is limited by similar maximum theoretical efficiencies.
At the same time, a class of materials known as ferroelectrics can also convert sunlight to electricity (or fuels in photocatalytic processes). They utilise a fundamentally different mechanism to do this, known as the bulk photovoltaic effect (BPVE). However, despite many efforts to improve their efficiency, it generally lies well below 1%. One challenge is that most ferroelectrics are not able to absorb most visible light. More fundamentally, the underlying mechanism of the BPVE is also limited, potentially to even lower maximum efficiencies than conventional junction-based PVs.
In this project we take an innovative approach to overcome these dual efficiency limits. We draw on the proven ability for ferroelectrics to interact strongly with the semiconductors used in PVs and photocatalysts. As this interaction only occurs at the very small scale (on the order of nanometers), we are producing ‘nanocomposites’ of ferroelectrics and semiconductors to maximise the interactions. In these nanocomposites, the semiconductors absorb the light, and the high voltages generated by the ferroelectrics are used to drive a resulting photocurrent in the semiconductor. In this way we will demonstrate a new mechanism to generate electricity and fuels from solar energy. This has previously unexplored efficiency limits, and we will study the underlying science behind the effects to understand these and optimise the materials and devices. Therefore, the overall objectives are to:
1. Design and synthesise optimal ferroelectric nanostructures and gain control over their properties, including the BPVE, through careful study and tuning of the material properties in both precision model systems and low-cost materials;
2. Develop detailed device models to accurately describe and predict the behaviour of these novel devices, incorporating progressive knowledge and understanding throughout the project using both empirical data and computational modelling;
3. Use these models to predict the optimum materials, structures and designs to demonstrate this novel technology and optimise device performance;
4. Fabricate and test proof-of-concept devices based on these optimised designs to validate the models and prove the hypothesis, establishing a new frontier in solar energy generation and wider science.
Through this, the project will set out a new route to solar energy conversion that could lead to technologies in future that can convert solar energy to electricity or fuels at much higher efficiencies, thus accelerating the deployment of solar energy technologies.
At the same time, a class of materials known as ferroelectrics can also convert sunlight to electricity (or fuels in photocatalytic processes). They utilise a fundamentally different mechanism to do this, known as the bulk photovoltaic effect (BPVE). However, despite many efforts to improve their efficiency, it generally lies well below 1%. One challenge is that most ferroelectrics are not able to absorb most visible light. More fundamentally, the underlying mechanism of the BPVE is also limited, potentially to even lower maximum efficiencies than conventional junction-based PVs.
In this project we take an innovative approach to overcome these dual efficiency limits. We draw on the proven ability for ferroelectrics to interact strongly with the semiconductors used in PVs and photocatalysts. As this interaction only occurs at the very small scale (on the order of nanometers), we are producing ‘nanocomposites’ of ferroelectrics and semiconductors to maximise the interactions. In these nanocomposites, the semiconductors absorb the light, and the high voltages generated by the ferroelectrics are used to drive a resulting photocurrent in the semiconductor. In this way we will demonstrate a new mechanism to generate electricity and fuels from solar energy. This has previously unexplored efficiency limits, and we will study the underlying science behind the effects to understand these and optimise the materials and devices. Therefore, the overall objectives are to:
1. Design and synthesise optimal ferroelectric nanostructures and gain control over their properties, including the BPVE, through careful study and tuning of the material properties in both precision model systems and low-cost materials;
2. Develop detailed device models to accurately describe and predict the behaviour of these novel devices, incorporating progressive knowledge and understanding throughout the project using both empirical data and computational modelling;
3. Use these models to predict the optimum materials, structures and designs to demonstrate this novel technology and optimise device performance;
4. Fabricate and test proof-of-concept devices based on these optimised designs to validate the models and prove the hypothesis, establishing a new frontier in solar energy generation and wider science.
Through this, the project will set out a new route to solar energy conversion that could lead to technologies in future that can convert solar energy to electricity or fuels at much higher efficiencies, thus accelerating the deployment of solar energy technologies.
The work so far can be broadly divided into three main areas of activity:
1. Developing the methods to produce the nanocomposite materials for use in the project, including predicting the materials that are optimum to use using computational methods.
2. Measuring the properties of the materials that have been produced, both the understand their behaviour and their underlying mechanisms, and to demonstrate the BPVE effect and photocatalytic properties have been achieved.
3. Produce computational models in order to add to the understanding of the behaviour of the materials when combined with the measurements outlined in 2.
For area 1, to predict materials that will be compatible to form the ferroelectric-semiconductor nanocomposites we have used computational methods that can predict which materials will form a structurally compatible interface. This has allowed us to identify groups of materials that we can then move on to synthesise experimentally. For this synthesis, we have taken two approaches: making ideal, high-quality films using a processed called pulsed-laser deposition. This makes films of materials that have very regular structures. We have taken an innovative approach here to simultaneously deposit two materials that spontaneously separate into a nanocomposite film. We have measured the photovoltaic properties of these films, and demonstrated that they can show a BPVE for the first time. The other approach that we have taken is to use low-cost, chemical solution-based techniques to make ferroelectric films with nanoscale pores, which we can then fill with the semiconductors. We have successfully produced such films of one ferroelectric material and shown that we can control its ferroelectric properties. We have also shown that these films work as photocatalysts, and that their photocatalytic performance depends on their ferroelectric properties, which we can control. We have also filled the pores of these materials with a range of semiconductor photocatalysts and shown much better photocatalytic performance in the nanocomposite than in either single material, and again, that we can control the performance by changing the ferroelectric properties.
For area 2, we are carrying out a wide range of detailed measurements to understand how the ferroelectricity contributes to the performance of the materials. We have measured how effectively current is produced in the materials on very short timescales as a function of their ferroelectric properties, and how this relates to the internal mechanisms in the materials. We have also perfected an approach to measure the nanoscale ferroelectric properties so that we can use this to understand how the ferroelectrics and semiconductors interact.
For area 3, we have built atomic-scale models of the interfaces of a wide range of materials and used these to predict the structural and electronic properties of the interfaces. In order to model some of the interfaces that are relevant to the project it became necessary to develop new computational approaches, since such a large number of atoms were required to model the interfaces accurately that current approaches would not have been possible. We used this to predict the electronic properties of the materials across the interface, which we are producing experimentally.
1. Developing the methods to produce the nanocomposite materials for use in the project, including predicting the materials that are optimum to use using computational methods.
2. Measuring the properties of the materials that have been produced, both the understand their behaviour and their underlying mechanisms, and to demonstrate the BPVE effect and photocatalytic properties have been achieved.
3. Produce computational models in order to add to the understanding of the behaviour of the materials when combined with the measurements outlined in 2.
For area 1, to predict materials that will be compatible to form the ferroelectric-semiconductor nanocomposites we have used computational methods that can predict which materials will form a structurally compatible interface. This has allowed us to identify groups of materials that we can then move on to synthesise experimentally. For this synthesis, we have taken two approaches: making ideal, high-quality films using a processed called pulsed-laser deposition. This makes films of materials that have very regular structures. We have taken an innovative approach here to simultaneously deposit two materials that spontaneously separate into a nanocomposite film. We have measured the photovoltaic properties of these films, and demonstrated that they can show a BPVE for the first time. The other approach that we have taken is to use low-cost, chemical solution-based techniques to make ferroelectric films with nanoscale pores, which we can then fill with the semiconductors. We have successfully produced such films of one ferroelectric material and shown that we can control its ferroelectric properties. We have also shown that these films work as photocatalysts, and that their photocatalytic performance depends on their ferroelectric properties, which we can control. We have also filled the pores of these materials with a range of semiconductor photocatalysts and shown much better photocatalytic performance in the nanocomposite than in either single material, and again, that we can control the performance by changing the ferroelectric properties.
For area 2, we are carrying out a wide range of detailed measurements to understand how the ferroelectricity contributes to the performance of the materials. We have measured how effectively current is produced in the materials on very short timescales as a function of their ferroelectric properties, and how this relates to the internal mechanisms in the materials. We have also perfected an approach to measure the nanoscale ferroelectric properties so that we can use this to understand how the ferroelectrics and semiconductors interact.
For area 3, we have built atomic-scale models of the interfaces of a wide range of materials and used these to predict the structural and electronic properties of the interfaces. In order to model some of the interfaces that are relevant to the project it became necessary to develop new computational approaches, since such a large number of atoms were required to model the interfaces accurately that current approaches would not have been possible. We used this to predict the electronic properties of the materials across the interface, which we are producing experimentally.
We have made substantial progress beyond the state of the art. We have developed new ways to produce ferroelectric-semiconductor films for solar energy applications using both solution-based and PLD techniques. For the solution-based films, this has opened up new ways to configure these materials combinations at the nanoscale, which is leading to new understanding of how the light response of the ferroelectric materials can enhance the semiconductor photocatalytic performance. For the PLD films, we have demonstrated the BPVE in a nanostructured ferroelectric thin film for the first time, which is both critical for the project and will open up new opportunity for innovative device design. The new computational approaches will also allow more complex materials interfaces to be modelled in the future, which will have impact on many areas.
In the future, we will continue to predict more material combinations that could work well for the project’s target applications. These will then be produced and studied in detail to expand the understanding of the interactions. Now that the experimental methods are established in the project, we will study the materials’ properties in much more detail and combine with more complex computational models to build further understanding of how the ferroelectric and semiconductor materials interact. We will also expand the focus more on applications – producing more optimised material combinations for photocatalysis, and combining the nanostructured materials with optimal PV materials to make new types of nanocomposite PV devices. Through this combined work we will both enhance the performance of this new type of device, and build an in-depth understanding of their underlying mechanisms.
In the future, we will continue to predict more material combinations that could work well for the project’s target applications. These will then be produced and studied in detail to expand the understanding of the interactions. Now that the experimental methods are established in the project, we will study the materials’ properties in much more detail and combine with more complex computational models to build further understanding of how the ferroelectric and semiconductor materials interact. We will also expand the focus more on applications – producing more optimised material combinations for photocatalysis, and combining the nanostructured materials with optimal PV materials to make new types of nanocomposite PV devices. Through this combined work we will both enhance the performance of this new type of device, and build an in-depth understanding of their underlying mechanisms.