Defect Tolerant Semiconductors for Solar Energy Conversion

Abstract

Defect tolerance is the tendency of a semiconductor to keep its properties despite the presence of crystallographic defects. Scientific understanding of the origin of defect tolerance is currently missing. Here we show that semiconductors with antibonding states at the top of the valence band are likely to be tolerant to defects. Theoretical calculations demonstrate that Cu3N with antibonding valence band maximum has shallow intrinsic defects and no surface states, in contrast to GaN with bonding valence band maximum. Experimental measurements indicate shallow native donors and acceptors in Cu3N thin films, leading to 10(16)-10(17) cm(-3) doping with either electrons or holes depending on the growth conditions. The experimentally measured bipolar doping and the solar-matched optical absorption onset (1.4 eV) make Cu3N a promising candidate absorber for photovoltaic and photoelectrochemical solar cells, despite the calculated indirect fundamental band gap (1.0 eV). These conclusions can be extended to other materials with antibonding character of the valence band, defining a class of defect-tolerant semiconductors for solar energy conversion applications.

Octahedral and trigonal-prismatic coordination preferences in Nb-, Mo-, Ta-, and W-based ABX2 layered oxides, oxynitrides, and nitrides

“…The 3d metals can be considered to be divalent cations considering their ionic radii, and, if so, the electron count of the d orbitals of Mo and W would be close to d 2 and these could follow the structural rule found in this work, i.e., the relationship between the d electron count of the 4d/5d metal and octahedral/trigonal coordination. Their octahedral sites might be somewhat flexible with respect to the vacancies, and substitution in the octahedral sites has been reported in FexWN2 [55,56] Additionally, some nitrides with monovalent transition metals (i.e., Cu/Ag) can be understood similarly, e.g., CuNbN2 [61,62], CuTaN2 [63], and AgTaN2 [64,65]. We could treat these as d 0 compounds, and they have octahedral (Nb/Ta)-N planes, as expected.…”

“…The d 0 nitrides show semiconductive behavior, and their visible or infrared absorption properties show the potential for solar energy conversion [61,62]. SrZrN2 and SrHfN2, which are isostructural with NaNbN2, have been computationally predicted to be thermoelectronic materials [67].…”

Defect-Tolerant Monolayer Transition Metal Dichalcogenides

“…This picture also agrees with previous works on defect tolerance in semiconductors. [46] The correspondence between the orbital character of the bands and the defect tolerance can states in a given energy window from E 1 to E 2 we introduce the orbital fingerprint vector,…”

Research Update: Bismuth-based perovskite-inspired photovoltaic materials

“…With this electronic structure, intrinsic defects (e.g., I vacancies) are likely to form close to the band edge or to be resonant within the valence band. [17][18][19] The energetic distance of defects from the band edge is further reduced by spin-orbit coupling due to the heavy Pb 2+ cation, which results in greater band-dispersion. This contrasts with the electronic structure of traditional semiconductors, in which the bonding-antibonding orbital pair is formed across the bandgap [ Fig.…”

“…Dangling bonds from defects in these traditional semiconductors (e.g., GaAs) are then likely to form transition levels close to mid-gap, which lead to high rates of Shockley-Read-Hall recombination. 17,18 It has been hypothesized that the defect-tolerant perovskite electronic structure could be replicated in materials consisting of a heavy metal cation with a stable pair of valence s electrons. 18 Searches through the Materials Genome database for materials with a significant fraction of s orbitals in the density of states at the valence band maximum identified bismuth-based compounds as promising.…”