(559e) Low Temperature Solution Processed Synthesis of Chalcogenide Perovskites Using Organometallic Precursors

Chalcogenide perovskites are a class of materials that have recently gained great interest for photovoltaic applications due to their high stabilities and excellent predicted optoelectronic properties, including a direct band gap, high near-band edge absorption coefficients, and good carrier transport.^1–3 This class of materials has the general formula of ABX₃, where A is a divalent cation such as Ca²⁺, Sr²⁺, or Ba²⁺, B is a tetravalent cation such as Ti⁴⁺, Zr⁴⁺, or Hf⁴⁺, and X is a divalent anion such as S^2- or Se^2-. ABX₃ chalcogenide materials can form a variety of crystal structures⁴, but only those with corner-sharing BX₆ octahedra have the distorted perovskite crystal structure and are expected to have the excellent optoelectronic properties that make them ideal candidates for absorber materials in thin film solar cells. In literature, only CaZrS₃, CaHfS₃, SrZrS₃, SrHfS₃, BaZrS₃, and BaHfS₃, have been experimentally made in the distorted perovskite phase with the most studied material being BaZrS₃ due to its high thermodynamic favorability and lower synthesis temperatures.⁵ BaZrS₃ has a bandgap of 1.8 eV, making it an excellent wide-bandgap partner for a silicon-based tandem solar cell.^3,5 One of the greatest challenges with using chalcogenide perovskites for applications in solar cells is that their high stability goes hand-in-hand with higher synthesis temperatures, and even the lowest temperature synthesis for BaZrS₃, reported in literature by Niu et. al., required a temperature of 600°C and a reaction time of 60 hours in the presence of an iodine catalyst.⁶In this conference paper, we present a novel solution-processed route to synthesize BaZrS₃ at temperatures of 575°C and sulfurization times as short as one hour.

Our synthesis procedure utilizes organometallic barium and zirconium precursors dissolved in a sulfur containing solvent to create a molecular precursor ink. This ink is blade coated onto a glass substrate and annealed in a sulfur containing atmosphere at 575°C for times ranging from 1 hour to 16 hours to produce BaZrS₃. The resulting material shows a PXRD diffraction pattern with no obvious secondary phases and a Raman spectrum that matches with previously reported standards. The synthesized BaZrS₃ has a photoluminescence peak centered at 1.77 eV with a 0.4 eV FWHM.

In conclusion, we have developed a solution-processed approach to produce BaZrS₃ in the distorted perovskite phase and the Ba₃Zr₂S₇ Ruddlesden-Popper phase at 575°C. Continuing work will focus on using this solution-processed approach to synthesize other chalcogenide perovskite materials including CaZrS₃, CaHfS₃, SrZrS₃, SrHfS₃, and BaHfS_3, and on further characterizing the properties of the synthesized chalcogenide perovskite films.

(1) Wei, X.; Hui, H.; Perera, S.; Sheng, A.; Watson, D. F.; Sun, Y.-Y.; Jia, Q.; Zhang, S.; Zeng, H. Ti-Alloying of BaZrS3 Chalcogenide Perovskite for Photovoltaics. ACS Omega 2020, 5 (30), 18579–18583. https://doi.org/10.1021/acsomega.0c00740.

(2) Meng, W.; Saparov, B.; Hong, F.; Wang, J.; Mitzi, D. B.; Yan, Y. Alloying and Defect Control within Chalcogenide Perovskites for Optimized Photovoltaic Application. Chemistry of Materials 2016, 28 (3), 821–829. https://doi.org/10.1021/acs.chemmater.5b04213.

(3) Sun, Y.-Y.; Agiorgousis, M. L.; Zhang, P.; Zhang, S. Chalcogenide Perovskites for Photovoltaics. Nano Letters 2015, 15 (1), 581–585. https://doi.org/10.1021/nl504046x.

(4) Brehm, J. A.; Bennett, J. W.; Schoenberg, M. R.; Grinberg, I.; Rappe, A. M. The Structural Diversity of AB S 3 Compounds with d 0 Electronic Configuration for the B -Cation. The Journal of Chemical Physics 2014, 140 (22), 224703. https://doi.org/10.1063/1.4879659.

(5) Sopiha, K. v; Comparotto, C.; Márquez, J. A.; Scragg, J. J. S. Chalcogenide Perovskites: Tantalizing Prospects, Challenging Materials. Advanced Optical Materials. December 13, 2021, p 2101704. https://doi.org/10.1002/adom.202101704.

(6) Niu, S.; Huyan, H.; Liu, Y.; Yeung, M.; Ye, K.; Blankemeier, L.; Orvis, T.; Sarkar, D.; Singh, D. J.; Kapadia, R.; Ravichandran, J. Bandgap Control via Structural and Chemical Tuning of Transition Metal Perovskite Chalcogenides. Advanced Materials 2017, 29 (9), 1604733. https://doi.org/10.1002/adma.201604733.