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.
