Periodic Reporting for period 1 - IRPV (Chalcogenide-perovskites for infrared photovoltaics)
Reporting period: 2020-05-04 to 2022-05-03
Currently, the energy generated from renewable sources is of critical importance to the carbon-neutral and sustainable future society. Wind and solar energies are the fastest-growing markets with deployment of over 100 GW every year worldwide. The main technology in capturing solar energy is based on the photovoltaic (PV) effect and a typical high-end solar cell has about 25% of energy conversion efficiency. Building solar parks on hundreds of GW scale, thus requires very large territories which leads to a more negative effect on the environment and competition with agriculture for land use. Therefore, it is essential to increase the efficiency and longevity of current solar cells to mitigate the impact of the solar energy sector.
The only working PV technology that can go beyond 30% efficiency is realised by stacking multiple solar cells together – a device known as a multijunction solar cell (MJSC). Immense resources are being dedicated to the development of tandem MJSC (crystalline Si + metal halide perovskite) which are designed to exploit the visible portion of the Sun’s spectrum more effectively, but the infrared part is completely neglected. Optimized solar cell technology working in the short-wavelength infrared region could significantly boost the overall efficiency of MJSC allowing it to approach 40%.
Established technologies and materials that can be employed in infrared solar cells are either composed of expensive and/or hazardous elements, or their fabrication costs are extremely high. Considering that the deployment level of solar energy has reached over 100 GW per year, technologies capable of supporting this demand should be pursued. Therefore, the IRPV project aims to explore novel materials for infrared solar cells. Researchers targeted a material class known as chalcogenides with a specific chemical structure – ABX3, where A and B are metals and X is sulphur or selenium. These materials were theoretically predicted to have suitable optoelectronic properties for PV application and the goal of the IRPV project was to synthesize and study them.
The only working PV technology that can go beyond 30% efficiency is realised by stacking multiple solar cells together – a device known as a multijunction solar cell (MJSC). Immense resources are being dedicated to the development of tandem MJSC (crystalline Si + metal halide perovskite) which are designed to exploit the visible portion of the Sun’s spectrum more effectively, but the infrared part is completely neglected. Optimized solar cell technology working in the short-wavelength infrared region could significantly boost the overall efficiency of MJSC allowing it to approach 40%.
Established technologies and materials that can be employed in infrared solar cells are either composed of expensive and/or hazardous elements, or their fabrication costs are extremely high. Considering that the deployment level of solar energy has reached over 100 GW per year, technologies capable of supporting this demand should be pursued. Therefore, the IRPV project aims to explore novel materials for infrared solar cells. Researchers targeted a material class known as chalcogenides with a specific chemical structure – ABX3, where A and B are metals and X is sulphur or selenium. These materials were theoretically predicted to have suitable optoelectronic properties for PV application and the goal of the IRPV project was to synthesize and study them.
The main activities in the first stage of the project were focused on synthesizing and studying ABX3 compounds. A method called solid-state reaction, where elements constituting the compound are inserted in the quartz tube, sealed and annealed, was employed to synthesize a series of ABX3 materials. Each compound because of its different thermodynamic properties required the optimisation of annealing temperature, time and composition separately. As a result, under optimised annealing conditions high purity samples were obtained for SrTiS3, (SnS)1.2TiS2 Sn(Ti,Zr)Se3, SrZrSe3 and SnZrS3. These materials were studied in terms of their structural and optical properties and it was found that in contrast to oxide or halide perovskites, the ABX3 chalcogenides studied in this project crystallised in hexagonal, needle-like or layered misfit structures. The measurements of the material’s optical properties revealed that compounds with a needle-like structure had a bandgap closer to the optimal value. In contrast, those with hexagonal or misfit phases were unsuitable for infrared solar cells. Considering material properties such as bandgap, phase stability, absorption coefficient, chemical composition, the selected material for further study was SnZrSe3.
To maximize the efficiency of the infrared solar cell, absorber material should be capable of absorbing in short-wavelength infrared region. To fine-tune the optical properties of SnZrSe3 for a targeted region, further optimisation in the composition and synthesis process was carried out. Ti was incorporated into the SnZrSe3 structure to create Sn(Zr,Ti)Se3 solid solution, and optoelectronic properties were studied with respect to the Zr/Ti ratio. It was found that with an increase in Ti concentration, the absorption edge of Sn(Zr,Ti)Se3 shifted towards the infrared region. Photodetector fabricated based on the alloy with the highest Ti concentration was sensitive in short-wavelength infrared region showing evident photo response. These results showcased that Sn(Zr,Ti)Se3 enjoys a wide range of spectral tunability and is an exciting material candidate for infrared solar cell application.
Further investigation in the IRPV project concentrated on producing SnZrSe3 thin films. Various deposition methods such as thermal evaporation, close-space sublimation and pulsed laser deposition were employed to achieve SnZrSe3 thin films. Different synthesis strategies were explored to understand the peculiarities of SnZrSe3 deposition mechanisms and to find the optimal approach. It was discovered that due to the different chemical nature of elements comprising SnZrSe3, it decomposed during the deposition process. Because evaporation temperatures of decomposition products were very distinct, the coherent deposition could not be realised for SnZrSe3 with methods explored in this project. However, it provided valuable knowledge and experience for the future development of SnZrSe3 films.
In summary, a novel material composed of abundant, inexpensive and low-toxicity elements was synthesized and studied in the IRPV project. It was demonstrated that Sn(Zr,Ti)Se3 featured PV-relevant characteristics suitable for infrared solar cell application.
Results generated in the IRPV project were presented at five international science conferences and reported in two peer-reviewed scientific publications.
To maximize the efficiency of the infrared solar cell, absorber material should be capable of absorbing in short-wavelength infrared region. To fine-tune the optical properties of SnZrSe3 for a targeted region, further optimisation in the composition and synthesis process was carried out. Ti was incorporated into the SnZrSe3 structure to create Sn(Zr,Ti)Se3 solid solution, and optoelectronic properties were studied with respect to the Zr/Ti ratio. It was found that with an increase in Ti concentration, the absorption edge of Sn(Zr,Ti)Se3 shifted towards the infrared region. Photodetector fabricated based on the alloy with the highest Ti concentration was sensitive in short-wavelength infrared region showing evident photo response. These results showcased that Sn(Zr,Ti)Se3 enjoys a wide range of spectral tunability and is an exciting material candidate for infrared solar cell application.
Further investigation in the IRPV project concentrated on producing SnZrSe3 thin films. Various deposition methods such as thermal evaporation, close-space sublimation and pulsed laser deposition were employed to achieve SnZrSe3 thin films. Different synthesis strategies were explored to understand the peculiarities of SnZrSe3 deposition mechanisms and to find the optimal approach. It was discovered that due to the different chemical nature of elements comprising SnZrSe3, it decomposed during the deposition process. Because evaporation temperatures of decomposition products were very distinct, the coherent deposition could not be realised for SnZrSe3 with methods explored in this project. However, it provided valuable knowledge and experience for the future development of SnZrSe3 films.
In summary, a novel material composed of abundant, inexpensive and low-toxicity elements was synthesized and studied in the IRPV project. It was demonstrated that Sn(Zr,Ti)Se3 featured PV-relevant characteristics suitable for infrared solar cell application.
Results generated in the IRPV project were presented at five international science conferences and reported in two peer-reviewed scientific publications.
Throughout the project, data about the synthesis and properties of ABX3 compounds were collected broadening the fundamental knowledge of chalcogenide materials, specifically with ABX3 chemical structure. Having identified the promising material candidate for infrared solar cells, increases the innovation capacity for the development of ultra-high efficiency solar cell technologies. As such, project outcomes have high technological relevance potentially strengthening the competitiveness of Si-based PV R&D companies and research centres. Increasing the solar cell efficiency would help to reduce the cost of renewable energy and mitigate the negative impact on the environment which is one of the priority directions in European Commission’s solar energy strategy.