Thermodynamic Stability Trend of Cubic Perovskites

Stability is of central importance in current perovskite solar cell research and applications. Goldschmidt tolerance factor (<i>t</i>) recently provided qualitative guidance for experimentalists to engineer stable ABX₃ perovskite by tuning effective ionic size with mixing cations or anions and for theorists to search emerging perovskites. Through first-principles calculations, we have calculated decomposition energies of 138 perovskite compounds of potential solar cell applications. Instead of <i>t</i>, we have found that (μ + <i>t</i>)^η, where μ and η are the octahedral factor and the atomic packing fraction, respectively, demonstrates a remarkably linear correlation with thermodynamic stability. As a stability descriptor, (μ + <i>t</i>)^η is able to predict the relative stability among any two perovskites with an accuracy of ∼90%. This trend is then used to predict decomposition energies of another 69 perovskites, and the results are in excellent agreement with first-principles calculations, indicating the generalization of the trend. This thermodynamic stability trend may help the efficient high-throughput search for emerging stable perovskites and precise control of chemical compositions for stabilizing current perovskites

Direct Observation of Group‑V Dopant Substitutional Defects in CdTe Single Crystals

Point defect chemistry strongly affects the fundamental properties of materials and has a decisive impact on device performance. The Group-V dopant is prominent acceptor species with high hole concentration in CdTe; however, its local atomic structure is still not clear owing to difficulties in definitive measurements and discrepancies between experimental observations and theoretical models. Herein, we report on direct observation of the local structure for the As dopant in CdTe single crystals by the X-ray fluorescence holography (XFH) technique, which is a powerful tool to visualize three-dimensional atomic configurations around a specific element. The XFH result shows the As substituting on both Cd (AsCd) and Te (AsTe) sites. Although AsTe has been well known as a shallow acceptor, AsCd has not attracted much attention and been discussed so far. Our results provide new insights into point defects by expanding the experimental XFH study in combination with theoretical first-principles studies in II–VI semiconductors