Nitride semiconductors are a promising class of materials for solar energy conversion applications, such as photovoltaic and photoelectrochemical cells. Nitrides can have better solar absorption and ...electrical transport properties than the more widely studied oxides, as well as the potential for better scalability than other pnictides or chalcogenides. In addition, nitrides are also relatively unexplored compared to other chemistries, so they provide a great opportunity for new materials discovery. This paper reviews the recent advances in the design of novel semiconducting nitrides for solar energy conversion technologies. Both binary and multinary nitrides are discussed, with a range of metal chemistries (Cu
3
N, ZnSnN
2
, Sn
3
N
4
,
etc.
) and crystal structures (delafossite, perovskite, spinel,
etc.
), including a brief overview of wurtzite III-N materials and devices. The current scientific challenges and promising future directions in the field are also highlighted.
Nitride semiconductors have properties suitable for solar energy conversion and can be synthesized using high-energy precursors.
Triple ionic-electronic conductors (TIECs) are materials that can simultaneously transport electronic species alongside two ionic species. The recent emergence of TIECs provides intriguing ...opportunities to maximize performance in a variety of electrochemical devices, including fuel cells, membrane reactors and electrolysis cells. However, the potential application of these nascent materials is limited by lack of fundamental knowledge of their transport properties and electrocatalytic activity. The goal of this Review is to summarize and analyse the current understanding of TIEC transport and electrochemistry in single-phase materials, including defect formation and conduction mechanisms. We particularly focus on the discovery criteria (for example, crystal structure and ion electronegativity), design principles (for example, cation and anion substitution chemistry) and operating conditions (for example, atmosphere) of materials that enable deliberate tuning of the conductivity of each charge carrier. Lastly, we identify important areas for further advances, including higher chemical stability, lower operating temperatures and discovery of n-type TIEC materials.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Inorganic nitrides with wurtzite crystal structures are well-known semiconductors used in optical and electronic devices. In contrast, rocksalt-structured nitrides are known for their superconducting ...and refractory properties. Breaking this dichotomy, herewe report ternary nitride semiconductors with rocksalt crystal structures, remarkable electronic properties, and the general chemical formula MgₓTM
1−xN (TM = Ti, Zr, Hf, Nb). Our experiments show that these materials form over a broad metal composition range, and that Mg-rich compositions are nondegenerate semiconductors with visible-range optical absorption onsets (1.8 to 2.1 eV) and up to 100 cm² V−1·s−1 electron mobility for MgZrN₂ grown on MgO substrates. Complementary ab initio calculations reveal that these materials have disorder-tunable optical absorption, large dielectric constants, and electronic bandgaps that are relatively insensitive to disorder. These ternary MgₓTM
1−xN semiconductors are also structurally compatible both with binary TMN superconductors and main-group nitride semiconductors along certain crystallographic orientations. Overall, these results highlight MgₓTM
1−xN as a class of materials combining the semiconducting properties of main-group wurtzite nitrides and rocksalt structure of superconducting transition-metal nitrides.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Compared to oxides, the nitrides are relatively unexplored, making them a promising chemical space for novel materials discovery. Of particular interest are nitrogen-rich nitrides, which often ...possess useful semiconducting properties for electronic and optoelectronic applications. However, such nitrogen-rich compounds are generally metastable, and the lack of a guiding theory for their synthesis has limited their exploration. Here, we review the remarkable metastability of observed nitrides, and examine the thermodynamics of how reactive nitrogen precursors can stabilize metastable nitrogen-rich compositions during materials synthesis. We map these thermodynamic strategies onto a predictive computational search, training a data-mined ionic substitution algorithm specifically for nitride discovery, which we combine with grand-canonical DFT-SCAN phase stability calculations to compute stabilizing nitrogen chemical potentials. We identify several new nitrogen-rich binary nitrides for experimental investigation, notably the transition metal nitrides Mn3N4, Cr3N4, V3N4, and Nb3N5, the main group nitride SbN, and the pernitrides FeN2, CrN2, and Cu2N2. By formulating rational thermodynamic routes to metastable compounds, we expand the search space for functional technological materials beyond equilibrium phases and compositions.
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IJS, KILJ, NUK, PNG, UL, UM
Exploratory synthesis in new chemical spaces is the essence of solid-state chemistry. However, uncharted chemical spaces can be difficult to navigate, especially when materials synthesis is ...challenging. Nitrides represent one such space, where stringent synthesis constraints have limited the exploration of this important class of functional materials. Here, we employ a suite of computational materials discovery and informatics tools to construct a large stability map of the inorganic ternary metal nitrides. Our map clusters the ternary nitrides into chemical families with distinct stability and metastability, and highlights hundreds of promising new ternary nitride spaces for experimental investigation-from which we experimentally realized seven new Zn- and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity and covalency of solid-state bonding from the density functional theory (DFT)-computed electron density, we reveal the complex interplay between chemistry, composition and electronic structure in governing large-scale stability trends in ternary nitride materials.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Electronic structure theory has recently been used to propose hypothetical compounds in presumed crystal structures, seeking new useful functional materials. In some cases, such hypothetical ...materials are metastable, albeit with technologically useful long lifetimes. Yet, in other cases, suggested hypothetical compounds may be significantly higher in energy than their lowest‐energy crystal structures or competing phases, making their synthesis and eventual device‐stability questionable. By way of example, the focus here is on the family of 1:1:1 compounds ABX called “filled tetrahedral structure” (sometimes called Half‐Heusler) in the four groups with octet electron count: I‐I‐VI (e.g., CuAgSe), I‐II‐V (e.g., AgMgAs), I‐III‐IV (e.g., LiAlSi), and II‐II‐IV (e.g., CaZnSn). First‐principles thermodynamics is used to sort the lowest‐energy structure and the thermodynamic stability of the 488 unreported hypothetical ABX compounds, many of which were previously proposed to be useful technologically. It is found that as many as 235 of the 488 are unstable with respect to decomposition (hence, are unlikely to be viable technologically), whereas other 235 of the unreported compounds are predicted to be thermodynamically stable (hence, potentially interesting new materials). 18 additional materials are too close to determine. The electronic structures of these predicted stable compounds are evaluated, seeking potential new material functionalities.
First‐principles thermodynamics is used to determine the lowest‐energy structures and stability with respect to decomposition of 488 hypothetical ABX Half‐Heusler compounds from the groups I‐I‐VI, I‐II‐V, I‐III‐IV, II‐II‐IV and it is found that 235 are unstable against decomposition and 18 are too close to determine. 235 other unreported (UR) compounds are predicted to be new stable phases. The electronic structures of these predicted new compounds are evaluated, seeking potential new material functionalities.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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 1016–1017 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.
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IJS, KILJ, NUK, PNG, UL, UM
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