Multifunctional double perovskites Cs2BI6 (B = Ti, Ge, Se, Sn, and Te) for solar energy harvesting: photovoltaic, photocatalytic, and thermoelectric pathways

The following work utilizes density functional theory (DFT) to examine the photovoltaic, photocatalytic, and thermoelectric performance of five multifunctional vacancy-ordered double perovskites: Cs2TiI6, Cs2GeI6, Cs2SeI6, Cs2SnI6, and Cs2TeI6. The study analyzes the structural, elastic, electronic, optical, photovoltaic, photocatalytic, and thermoelectric characteristics. This investigation was conducted using the WIEN2k software with the GGA-mBJ approximation. The photovoltaic performance of the materials was assessed by calculating the power conversion efficiency (PCE) based on the Shockley-Queisser (S-Q) and the Spectroscopic Limited Maximum Efficiency (SLME) models. The water splitting potential was evaluated by computing the solar-to-hydrogen efficiency (STH). At the same time, the thermoelectric performance was quantified by calculating various parameters, focusing on the Figure of Merit (ZT). The findings indicate that Cs2TiI6 is a good choice as a solar cell absorber with a PCE of 29.84 according to the SLME approximation. Cs2SeI6, Cs2SnI6, and Cs2TeI6 are highly suitable for water splitting. Cs2TiI6 is the best candidate for CO2 photoreduction at pH = 0. Finally, Cs2SnI6 and Cs2TiI6 are the best for thermoelectric conversion with a ZT value of 0.768. This investigation highlights the potential of multifunctional double perovskites for photovoltaic, photocatalytic, and thermoelectric applications, offering promising prospects for next-generation energy solutions.