Bandgap tuning in Sn(Ti,Zr)Se 3 chalcogenide perovskite by cationic substitution Rokas Kondrotas 1 , Vidas Pakštas 1 , Remigijus Juškėnas 1 ,Arūnas Krotkus 1 , Artūras Suchodolskis 1 , Marius Franckevičius 1 , Katri Muska 2 , Xiaofeng Li 2 , Marit Kauk-Kuusik 2 , Algirdas Mekys 3 1 State Research Institute, Lithuania, 2 Tallinn University of Technology, Estonia, 3 Institute of Photonics and Nanotechnology, Lithuania Multi-junction solar cell design is currently the most viable strategy to surpass 30% power conversion efficiency (PCE). Combining wide bandgap perovskite solar cell with c-Si forming a tandem device allowed to achieve over 29% PCE 1 . However, the infrared part of solar spectrum (<1.1 eV) is not absorbed by such tandem device, that could otherwise add 5% in absolute PCE. Taking into account three-junction device architecture with c-Si as the middle sub-cell, the optimal bandgap for bottom sub-cell is 0.7 eV 2 . There are few materials with close to 0.7 eV bandgap much lest studied for low-cost high-efficiency photovoltaic application. In this work, we examined bandgap tuning possibilities in chalcogenide perovskite with an aim to obtain 0.7 eV bandgap. Inorganic chalcogenide perovskites with a general formula ABX 3 (X=S, Se) where A=Ca, Sr, Ba, B=Ti, Zr, Hf and X=Se, have been predicted to have bandgaps in 0.0 – 2.3 eV range 3 . However, low bandgap chalcogenide perovskites are rarely studied, and little is known about their optical properties from experimental perspective. In this work, we focus on synthesizing critical raw materials free and earth-abundant composition chalcogenide perovskite - Sn(Ti,Zr)Se 3 . Solid solutions of Sn(Ti,Zr)Se 3 were synthesized by solid state reaction. Crystalline phase composition and purity was confirmed using X-ray diffraction method and energy dispersive spectroscopy. Bandgap was estimated from diffuse reflectance measurements of powder. We found that within 0 to 0.25 Ti/(Ti+Zr) ratio range, Sn(Ti,Zr)Se 3 crystallized in a needle-like crystal structure (space group Pnma ) – the same as pure SnZrSe 3 . Estimated bandgap varied from 0.6 to 1.1 eV depending on the content of Ti. This showed that bandgap in Sn(Ti,Zr)Se 3 solid solution can be effectively tuned by cationic substitution and fined tuned to achieve 0.7 eV. References 1. Al-Ashouri A, Köhnen E, Li B, Magomedov A, Hempel H, Caprioglio P, et al. Monolithic perovskite/silicon tandem solar cell with> 29% efficiency by enhanced hole extraction. Science. 2020;370(6522):1300-9. 2. Guter W, Schöne J, Philipps SP, Steiner M, Siefer G, Wekkeli A, et al. Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight. Applied Physics Letters. 2009;94(22):223504. 3. Sun Y-Y, Agiorgousis ML, Zhang P, Zhang S. Chalcogenide perovskites for photovoltaics. Nano letters. 2015;15(1):581-5.
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