Recently, we and
others have proposed screening criteria for “defect-tolerant”
photovoltaic (PV) absorbers, identifying several classes of semiconducting
compounds with electronic structures similar to those of hybrid lead–halide
perovskites. In this work, we reflect on the accuracy and prospects
of these new design criteria through a combined experimental and theoretical
approach. We construct a model to extract photoluminescence lifetimes
of six of these candidate PV absorbers, including four (InI, SbSI,
SbSeI, and BiOI) for which time-resolved photoluminescence has not
been previously reported. The lifetimes of all six candidate materials
exceed 1 ns, a threshold for promising early stage PV device performance.
However, there are variations between these materials, and none achieve
lifetimes as high as those of the hybrid lead–halide perovskites,
suggesting that the heuristics for defect-tolerant semiconductors
are incomplete. We explore this through first-principles point defect
calculations and Shockley–Read–Hall recombination models
to describe the variation between the measured materials. In light
of these insights, we discuss the evolution of screening criteria
for defect tolerance and high-performance PV materials.
A superstructure can elicit versatile new properties of materials by breaking their original geometrical symmetries. It is an important topic in the layered graphene-like two-dimensional transition-metal dichalcogenides (TMDs), but its origin remains unclear. Using diamond-anvil cell techniques, synchrotron x-ray diffraction, x-ray absorption, and the first-principles calculations, we show that the evolution from the weak Van der Waals bonding to the Heisenberg covalent bonding between layers induces an isostructural transition in quasi-twodimensional 1T-type VSe 2 at high pressure. Furthermore, our results show that high-pressure induce a novel superstructure at 15.5 GPa, rather than suppress as it would normally, which is unexpected. It is driven by the Fermi surface nesting, enhanced by the pressure-induced distortion. The results suggest that the superstructure not only appears in the two-dimensional structure but also can emerge in the pressure-tuned three-dimensional structure with new symmetry and develop superconductivity.
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