Unexpectedly Strong Auger Recombination in Halide Perovskites

The emergence of halide perovskites for photovoltaic applications has triggered great interest in these materials for solidâ state light emission. Higher order electronâ hole recombination processes can critically affect the efficiency of such devices. In the present work, the Auger recombination coefficients are computed in the prototypical halide perovskite, CH3NH3PbI3 (MAPbI3), using firstâ principles calculations. It is demonstrated that Auger recombination is responsible for the exceptionally high thirdâ order recombination coefficient observed in experiment. The large Auger coefficient is attributed to a coincidental resonance between the bandgap and interband transitions to a complex of higherâ lying conduction bands. Additionally, it is found that the distortions of PbI6 octahedra contribute significantly to the high Auger coefficient, offering potential avenues for materials design.The unexpectedly high thirdâ order recombination coefficient in halide perovskites is identified to stem from Auger recombination. Firstâ principles calculations show that the large Auger coefficient originates from a coincidental resonance as well as from distortions in the metalâ halide lattice. These insights point to avenues for improved materials design.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146455/1/aenm201801027_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146455/2/aenm201801027.pd

A representation-independent electronic charge density database for crystalline materials

In addition to being the core quantity in density functional theory, the charge density can be used in many tertiary analyses in materials sciences from bonding to assigning charge to specific atoms. The charge density is data-rich since it contains information about all the electrons in the system. With increasing utilization of machine-learning tools in materials sciences, a data-rich object like the charge density can be utilized in a wide range of applications. The database presented here provides a modern and user-friendly interface for a large and continuously updated collection of charge densities as part of the Materials Project. In addition to the charge density data, we provide the theory and code for changing the representation of the charge density which should enable more advanced machine-learning studies for the broader community

Designing transparent conductors using forbidden optical transitions

Many semiconductors present weak or forbidden transitions at their fundamental band gaps, inducing a widened region of transparency. This occurs in high-performing n-type transparent conductors (TCs) such as Sn-doped In2O3 (ITO), however thus far the presence of forbidden transitions has been neglected in searches for new p-type TCs. To address this, we first compute high-throughput absorption spectra across ~18,000 semiconductors, showing that over half exhibit forbidden or weak optical transitions at their band edges. Next, we demonstrate that compounds with highly localized band edge states are more likely to present forbidden transitions. Lastly, we search this set for p-type and n-type TCs with forbidden or weak transitions. Defect calculations yield unexplored TC candidates such as ambipolar BeSiP2, Zr2SN2 and KSe, p-type BAs, Au2S, and AuCl, and n-type Ba2InGaO5, GaSbO4, and KSbO3, among others. We share our data set via the MPContribs platform, and we recommend that future screenings for optical properties use metrics representative of absorption features rather than band gap alone