(353c) Advances in the Synthesis and Application of Solution-Processed Chalcogenide Perovskites

To unlock the potential of halide perovskites for solar power applications, it is essential to make them stable. Halide perovskites are cost-effective, easy to synthesize at low temperatures, and possess advantageous properties such as tunable light absorption and efficient charge transport. However, their instability in the presence of oxygen and moisture, coupled with the inclusion of toxic lead, raises environmental and durability concerns. Although recent advancements have improved their stability and reduced toxicity, further progress is needed to enable their widespread adoption in solar cell technologies.

The exceptional properties of halide perovskites stem from their unique crystal structure, inspiring researchers to explore alternative materials with similar characteristics. Chalcogenide perovskites, which share the same crystal structure but are composed of more abundant elements, have emerged as a promising alternative. These materials exhibit superior light absorption—often surpassing that of halide perovskites—and demonstrate remarkable stability in air, moisture, and high temperatures, making them highly suitable for solar cell applications, particularly in tandem systems.

Despite their potential, chalcogenide perovskites have historically been synthesized at high temperatures, rendering them incompatible with solar cell integration. Most studies have focused on evaluating their properties using powdered forms, and thin-film fabrication methods have also relied on high-temperature processes. A key challenge is their strong affinity for oxygen, which leads to the formation of unwanted oxide phases and alters the film’s composition. Additionally, existing synthesis methods have produced materials with a wide range of bandgaps, whereas the ideal bandgap for tandem solar applications is around 1.8 eV. Limited research has been conducted on low-temperature, cost-effective synthesis techniques, such as solution processing, as the chemical approaches used for many other chalcogenide materials, such as Cu(In,Ga)S₂, Cu₂ZnSnS₄, etc., are not well-suited to chalcogenide perovskites. This lack of understanding regarding low-temperature synthesis has significantly impeded progress in the field.

In our research, we investigated the factors influencing the high-temperature growth of these materials and identified several critical elements: precursor reactivity, the use of a liquid flux or transport agent, and the incorporation of an oxygen sink. By enhancing precursor reactivity and ensuring complete conversion, we developed methods to synthesize these materials at lower temperatures. The liquid flux facilitated growth at reduced temperatures by overcoming mass-transfer barriers, while the oxygen sink effectively removed oxide impurities. As a result, we successfully synthesized BaZrS₃ at temperatures below 600 °C, achieving uniform films with an ideal bandgap of 1.82 eV.

Additionally, we developed techniques for producing nanoparticles of various chalcogenide perovskites, broadening their potential for use in optoelectronic devices. Solution-processed BaZrS₃ demonstrated exceptional performance, exhibiting the fastest response times for photodetectors among comparable materials, as well as notable photoluminescence and carrier lifetime. We also successfully addressed the challenge of depositing thin films of these emerging compounds onto conductive substrates and are actively exploring their potential for optoelectronic applications. Furthermore, by alloying different elements with BaZrS₃ and BaHfS₃, we were able to tune their bandgaps, making them suitable for both single-junction and tandem solar cells. Our work represents a significant advancement in the application of these materials for optoelectronic technologies.