Periodic Reporting for period 4 - FREENERGY (Lead-free halide perovskites for the highest efficient solar energy conversion)
Période du rapport: 2022-11-01 au 2024-01-31
The main objective of FREENERGY is to demonstrate the use of tin-based halide perovskites for solar energy conversion with the highest efficiency. The shift from fossil fuels to sustainable energy sources is a significant challenge that society needs to tackle as soon as possible. Solar energy is one of the most promising sustainable energy sources, as it is abundant and available worldwide every day. Photovoltaic solar cells can directly convert sunlight into electricity using the photovoltaic effect in semiconducting materials. Silicon has been the dominant material for photovoltaic cells for many years. However, its high price initially limited large-scale energy production. Over time, the price of photovoltaic materials has decreased due to the use of new materials and fabrication procedures.
The development of novel materials and device concepts, drawing from and stimulating multiple disciplines, may lead to new opportunities for future photovoltaics. The design and fabrication of such materials and their integration into working devices are the guiding principles of the FREENERGY project.
The ultimate challenge for photovoltaics is to achieve the highest solar energy conversion efficiency, such as the 28.8% efficiency reached by GaAs solar cells, using inexpensive and environmentally friendly materials. The project leader believes that tin-based halide perovskites are the key to addressing this challenge. While tin-based halide perovskites have the potential to achieve this ambitious goal, their main drawback is the oxidative instability of tin. Therefore, FREENERGY proposes a groundbreaking approach to overcome this issue by developing new stable tin-based halide perovskites and demonstrating their use in high-efficiency solar cells.
The research strategy is twofold:
(i) The synthesis of new perovskite materials with a focus on engineering the perovskite lattice towards intrinsically more stable formulations.
(ii) The use of specific supramolecular interactions to control the microstructure of the material deposited in thin film and its interaction at the interface with other device components.
FREENERGY aims to demonstrate the potential of tin halide perovskites as photovoltaic materials by integrating materials, chemistry, and physics science. It ultimately targets the highest solar energy conversion efficiency with inexpensive and environmentally friendly solar cells.
The development of novel materials and device concepts, drawing from and stimulating multiple disciplines, may lead to new opportunities for future photovoltaics. The design and fabrication of such materials and their integration into working devices are the guiding principles of the FREENERGY project.
The ultimate challenge for photovoltaics is to achieve the highest solar energy conversion efficiency, such as the 28.8% efficiency reached by GaAs solar cells, using inexpensive and environmentally friendly materials. The project leader believes that tin-based halide perovskites are the key to addressing this challenge. While tin-based halide perovskites have the potential to achieve this ambitious goal, their main drawback is the oxidative instability of tin. Therefore, FREENERGY proposes a groundbreaking approach to overcome this issue by developing new stable tin-based halide perovskites and demonstrating their use in high-efficiency solar cells.
The research strategy is twofold:
(i) The synthesis of new perovskite materials with a focus on engineering the perovskite lattice towards intrinsically more stable formulations.
(ii) The use of specific supramolecular interactions to control the microstructure of the material deposited in thin film and its interaction at the interface with other device components.
FREENERGY aims to demonstrate the potential of tin halide perovskites as photovoltaic materials by integrating materials, chemistry, and physics science. It ultimately targets the highest solar energy conversion efficiency with inexpensive and environmentally friendly solar cells.
The fundamental scientific challenge addressed in FREENERGY is the oxidative stability of Sn2+ in halide perovskites under solar cell operation. State-of-the-art approaches aim to identify the best antioxidants to preserve the perovskite from external sources of degradation, such as oxygen and water, or reduce the interaction with them. While these approaches enabled longer material lifetimes, they did not directly face the intrinsic oxidative instability of Sn2+, resulting in the photovoltaic efficiency still being far from the real potential of this material.
The principal investigator pursued a strategy that tackles the challenge of tin oxidation from different angles, enabling the following main results:
1. Tuning the lattice parameters by engineering the perovskite composition. The oxidative stability of Sn2+ within the bulk of the perovskite crystals hinges on the formation energy of lattice defects. Enhancing the formation energy of the lattice defects enabled the reduction of defect concentration and thus the stabilization of the perovskite in solar cells' working condition. FREENERGY demonstrated that tin-based perovskite is intrinsically stable in solar cell working conditions.
2. Controlling the perovskite film microstructure by using small organic molecules as additives into the processing from solution. The defect concentrates at the surface of the crystalline grains forming the film of the perovskite into solar cells. Making a more uniform grain distribution reduces the amount of surfaces and, consequently, the concentration of defects, including the oxidized tin. This result and the resulting improved performance of tin-based perovskite solar cells were achieved by using small molecules to control the crystallization of the perovskite film.
3. The solar cells are made by interfacing the perovskite film with the other material components within the device. The chemical interaction of the perovskite with the other material comprising the device is critical for the functioning of the solar cells. The project made a critical contribution to the field, demonstrating a strategy to passivate and engineer the interface using specific supramolecular chemical interactions.
The main results described above have been reported in more than 20 peer-reviewed scientific publications addressing specific aspects of interest of FREENERGY. The principal investigator wrote a perspective peer-reviewed paper that provides an overall understanding of the results produced ("Stable Tin-Based Perovskite Solar Cells; ACS Energy Lett. 2023, 8, 4, 1896–1899"). In parallel to publications, the main advances of the project have been systematically presented at international conferences, disseminating the most advanced results and collecting the feedback of colleagues.
The principal investigator pursued a strategy that tackles the challenge of tin oxidation from different angles, enabling the following main results:
1. Tuning the lattice parameters by engineering the perovskite composition. The oxidative stability of Sn2+ within the bulk of the perovskite crystals hinges on the formation energy of lattice defects. Enhancing the formation energy of the lattice defects enabled the reduction of defect concentration and thus the stabilization of the perovskite in solar cells' working condition. FREENERGY demonstrated that tin-based perovskite is intrinsically stable in solar cell working conditions.
2. Controlling the perovskite film microstructure by using small organic molecules as additives into the processing from solution. The defect concentrates at the surface of the crystalline grains forming the film of the perovskite into solar cells. Making a more uniform grain distribution reduces the amount of surfaces and, consequently, the concentration of defects, including the oxidized tin. This result and the resulting improved performance of tin-based perovskite solar cells were achieved by using small molecules to control the crystallization of the perovskite film.
3. The solar cells are made by interfacing the perovskite film with the other material components within the device. The chemical interaction of the perovskite with the other material comprising the device is critical for the functioning of the solar cells. The project made a critical contribution to the field, demonstrating a strategy to passivate and engineer the interface using specific supramolecular chemical interactions.
The main results described above have been reported in more than 20 peer-reviewed scientific publications addressing specific aspects of interest of FREENERGY. The principal investigator wrote a perspective peer-reviewed paper that provides an overall understanding of the results produced ("Stable Tin-Based Perovskite Solar Cells; ACS Energy Lett. 2023, 8, 4, 1896–1899"). In parallel to publications, the main advances of the project have been systematically presented at international conferences, disseminating the most advanced results and collecting the feedback of colleagues.
Perovskite solar cells (PSCs) are approaching the power conversion efficiency of established technologies such as silicon, cadmium telluride (CdTe), and copper indium gallium selenide (CIGS). The next big challenge for PSCs is to create stable and efficient lead-free devices with more than 20% power conversion efficiency and 25 years of outdoor usage stability.
Several scientific works have proposed alternative lead-free compositions since the first demonstrations of lead halide perovskite as photovoltaic materials. Sn-based halide perovskites are among the most promising lead-free options. However, the oxidative stability of Sn2+ under solar cell operation needs to be addressed. State-of-the-art approaches to this challenge aim to identify the best antioxidants to preserve the perovskite from external sources of degradation, such as oxygen and water, or reduce the interaction with them. While these approaches have enabled longer material lifetimes, they have not directly addressed the intrinsic oxidative instability of Sn2+. As a result, the photovoltaic efficiency is still far from the real potential of this material.
By implementing the strategies described in the previous section, we achieved the following results beyond the state of the art:
1. Developed lead-free perovskite solar cells with a power conversion efficiency of over 15%. Higher efficiency is achieved only with the use of lead, which is not allowed by EU regulations on hazardous substances in electronics.
2. Replaced state-of-the-art solvents with green solvents for processing perovskite.
3. Achieved stable power output in solar cells' real working conditions. State-of-the-art devices suffer from early performance losses linked to the use of lead, which are solved by replacing lead entirely with tin.
Several scientific works have proposed alternative lead-free compositions since the first demonstrations of lead halide perovskite as photovoltaic materials. Sn-based halide perovskites are among the most promising lead-free options. However, the oxidative stability of Sn2+ under solar cell operation needs to be addressed. State-of-the-art approaches to this challenge aim to identify the best antioxidants to preserve the perovskite from external sources of degradation, such as oxygen and water, or reduce the interaction with them. While these approaches have enabled longer material lifetimes, they have not directly addressed the intrinsic oxidative instability of Sn2+. As a result, the photovoltaic efficiency is still far from the real potential of this material.
By implementing the strategies described in the previous section, we achieved the following results beyond the state of the art:
1. Developed lead-free perovskite solar cells with a power conversion efficiency of over 15%. Higher efficiency is achieved only with the use of lead, which is not allowed by EU regulations on hazardous substances in electronics.
2. Replaced state-of-the-art solvents with green solvents for processing perovskite.
3. Achieved stable power output in solar cells' real working conditions. State-of-the-art devices suffer from early performance losses linked to the use of lead, which are solved by replacing lead entirely with tin.