Machine Learning Aided Exploration of Chalcohalide-Based Solid Solutions for Photovoltaic Applications

Ternary chalcohalides, of general formula ABC (A = {Bi, Sb}, B = {S, Se}, C = {I, Br}), conform a new family of promising photovoltaic solar cell absorbers [1], with band-gaps lying between 1.5-1.9 eV and high absorption coefficients (∼10⁵ cm^-1).<br/><br/>Chalcohalide-based tandem solar cells have revolutioned the landscape of photovoltaic energy conversion in the past years as a promising alternative to single-junction silicon-based panels (e.g., tandem solar cells). Given the great stability of this novel family, solid solutions of chalcohalides [2], of general expression Bi_xSb_1-xS_ySe_1-yI_zBr_1-z, present extraordinary possibilities in terms of device tunability and efficiency, something that has not been explored so far to the best of our knowledge.<br/><br/>We present a comprehensive study of the energetic stability and optoelectronis properties of chalcohalide-based solid solutions covering all possible compositions that is based on a combination of first-principles calculations and novel deep learning techniques. Experimental validation is as well obtained from the synthesis and characterization of a solid-solution in the laboratory. Finally, a realistic BiSBr-BiSeI tandem device is optically simulated and optimized, showing a very competitive short-circuit current of 18.65 mA/cm².<br/><br/>[1] I. Caño-Prades, A. Navarro-Güell, E. Maggi et al., SbSeI and SbSeBr micro-columnar solar cells by a novel high pressure-based synthesis process, J. Mater. Chem. A, 2023, doi: 10.1039/D3TA03179A<br/>[2] I. Caño-Prades, P. Vidal-Fuentes, A. Gon-Medaille et al., Challenges and improvement pathways to develop quasi-1D (Sb1-xBix)2Se3-based materials for optically tuneable photovoltaic applications. Towards chalcogenide narrow-bandgap devices, Sol. Energy Mater. Sol. Cells., 2023, doi: 10.1016/j.solmat.2022.112150