2, Washington University in St. Louis, St. Louis, Missouri, United States
3, Washington University in St. Louis, St. Louis, Missouri, United States
4, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Lead-organohalide perovskites have been the subject of extensive research since the turn of the decade due to their promising electronic properties and affordable synthesis process. However, thermodynamic instability and lead toxicity issues have stifled their path to commercialization. Recently, Bismuth-based halide double perovskites have emerged as promising candidates for solar cell absorber materials. With Bi3+ being isoelectronic to Pb2+, these Bi-halide double perovskites, such as Cs2AgBiBr6, show comparable electronic properties to the lead-organohalide perovskites alleviating issues related to lead-toxicity. However, these halide double perovskites have indirect band gaps that are larger than the ideal 1.6 – 2.0 eV range required to efficiently use the solar spectrum. They are also observed to degrade over a period of weeks on exposure to ambient air and light.
In this work, we use the vast composition-space of all-inorganic double perovskite oxides containing bismuth to identify promising solar cell absorber materials. By screening through 100’s of hypothetical A'A"BBiO6 double perovskites using regression analysis and high-throughput density-functional theory (DFT) calculations, we predict a stable family of compounds with a general formula of A'A"TeBiO6, where A' is an alkali metal cation, such as Na, K, Rb and Cs, and A" is an alkaline-earth metal cation such as Mg, Ca, Sr and Ba. We predict an indirect band gap of 1.94 eV and 1.99 eV for KBaTeBiO6 and RbBaTeBiO6, respectively, which is comparable to the best performing Bi-halide double perovskite Cs2AgBiBr6 (2.06 eV). The effective mass of holes and electrons in case of KBaTeBiO6 is 0.25me and 0.28me, respectively, which is comparable to the mass of holes and electrons (0.14me and 0.37me, respectively) in Cs2AgBiBr6. We have successfully synthesized KBaTeBiO6 using wet-chemistry synthesis confirming its stability. Preliminary UV-vis measurements show an indirect band gap of 1.7 eV for the synthesized compound. In addition to these results, we will discuss the effect of composition on the electronic structure of these oxide double perovskites, including the role of defects. Our work demonstrates that inorganic Bi-based double perovskite oxides are promising benign alternatives to lead-halide perovskites for photovoltaic applications. It also highlights the combination of data-analytics and DFT calculations as a powerful approach to accelerate the discovery of promising materials.
This work was supported by a Ralph E. Powe Junior Faculty Enhancement Award from Oak Ridge Associated Universities to R.M. This work used computational resources of the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the National Science Foundation grant number ACI-1053575.