Identification of Potential Optoelectronic Applications for Metal Thiophosphates

Noncentrosymmetric Na6Pb3P4S16 and Centrosymmetric K2MIIP2S6 (MII = Mg and Zn) Displaying Multiple Membered-Ring Configurations and Strong Optical Anisotropy

Three thiophosphates including noncentrosymmetric Na6Pb3P4S16 and centrosymmetric K2MIIP2S6 (MII = Mg and Zn) were successfully synthesized in vacuum-sealed silica tubes. Note that interesting multiple six membered-rings (6-MRs) including 6-NaS6-MRs and 6-KSn-MRs (n = 6 and 7) formed by A+-centered polyhedra were discovered in the structures of title thiophosphates and these MR-composed three-dimensional (3D) tunnels show great possibility to facilitate the filling of various structural blocks (such as zero-dimensional (0D) Pb3S10 trimers or one-dimensional (1D) (MIISn)n chains). Na6Pb3P4S16 exhibits the strongest nonlinear optical (NLO) response (5.4 × AgGaS2) with phase-matching (PM) behavior among the known Pb-based PM NLO sulfides, which is much larger than that of Pb3P2S8 (3.5 × AgGaS2); it was verified that such large second harmonic generation (SHG) response in Na6Pb3P4S16 can be attributed to the huge contribution of stereochemically active PbS4 units based on the SHG-density and dipole-moment calculations. Moreover, title thiophosphates show large birefringences (Δn = 0.102-0.21), which indicates that incorporation of [P2S6] dimers or polarized PbS4 units into structures provides positive benefits for the onset of strong optical anisotropy.

2D Ultrawide Bandgap Semiconductors: Odyssey and Challenges

2D ultrawide bandgap (UWBG) semiconductors have aroused increasing interest in the field of high-power transparent electronic devices, deep-ultraviolet photodetectors, flexible electronic skins, and energy-efficient displays, owing to their intriguing physical properties. Compared with dominant narrow bandgap semiconductor material families, 2D UWBG semiconductors are less investigated but stand out because of their propensity for high optical transparency, tunable electrical conductivity, high mobility, and ultrahigh gate dielectrics. At the current stage of research, the most intensively investigated 2D UWBG semiconductors are metal oxides, metal chalcogenides, metal halides, and metal nitrides. This paper provides an up-to-date review of recent research progress on new 2D UWBG semiconductor materials and novel physical properties. The widespread applications, i.e., transistors, photodetector, touch screen, and inverter are summarized, which employ 2D UWBG semiconductors as either a passive or active layer. Finally, the existing challenges and opportunities of the enticing class of 2D UWBG semiconductors are highlighted.

M6PS5X (M = Ag, Cu; X = Cl, Br) chalcohalides exhibiting strong nonlinear optical responses and high laser damage resistances

A series of M₆PS₅X (M = Ag, Cu; X = Cl, Br) nonlinear optical (NLO) chalcohalides with special MS₃X ligands have been synthesized in this work. Their critical optical performances were systematically measured and the research results show that all of them exhibit strong NLO responses (2.0-2.7 × commercial AgGaS₂) and high laser-damage thresholds (1.7-2.3 × AgGaS₂), indicating their potential application as good NLO candidates. Furthermore, first-principles calculations were used to study their inherent structure-property relationships and chalcohalides can be expected to be optimal systems for the exploration of new promising IR NLO crystals.

Design of High-Performance Lead-Free Quaternary Antiperovskites for Photovoltaics via Ion Type Inversion and Anion Ordering

The emergence of halide double perovskites significantly increases the compositional space for lead-free and air-stable photovoltaic absorbers compared to halide perovskites. Nevertheless, most halide double perovskites exhibit oversized band gaps (>1.9 eV) or dipole-forbidden optical transition, which are unfavorable for efficient single-junction solar cell applications. The current device performance of halide double perovskite is still inferior to that of lead-based halide perovskites, such as CH₃NH₃PbI₃ (MAPbI₃). Here, by ion type inversion and anion ordering on perovskite lattice sites, two new classes of pnictogen-based quaternary antiperovskites with the formula of X₆B₂AA' and X₆BB'A₂ are designed. Phase stability and tunable band gaps in these quaternary antiperovskites are demonstrated based on first-principles calculations. Further photovoltaic-functionality-directed screening of these materials leads to the discovery of 5 stable compounds (Ca₆N₂AsSb, Ca₆N₂PSb, Sr₆N₂AsSb, Sr₆N₂PSb, and Ca₆NPSb₂) with suitable direct band gaps, small carrier effective masses and low exciton binding energies, and dipole-allowed strong optical absorption, which are favorable properties for a photovoltaic absorber material. The calculated theoretical maximum solar cell efficiencies based on these five compounds are all larger than 29%, comparable to or even higher than that of the MAPbI₃ based solar cell. Our work reveals the huge potential of quaternary antiperovskites in the optoelectronic field and provides a new strategy to design lead-free and air-stable perovskite-based photovoltaic absorber materials.

From thiophosphate to chalcohalide: mixed-anion AgSxCly ligands concurrently enhancing nonlinear optical effects and laser-damage threshold

In this study, we propose a new design strategy that introduces unique mixed-anion AgS_xCl_y ligands into thiophosphate to afford a successful synthesis of a promising Ag₅PS₄Cl₂ IR NLO chalcohalide. Compared with chlorine-free Ag₃PS₄, Ag₅PS₄Cl₂ undergoes overall performance enhancement and achieves a good balance between large NLO effect (2.0 × Ag₃PS₄) and high laser damage threshold (3.8 × Ag₃PS₄). Theoretical analysis further indicates that AgS_xCl_y groups are the new superior NLO-active units since they can maintain the wide bandgap while concurrently making a great contribution to the origin of NLO effects. Therefore, the incorporation of AgS_xCl_y groups into the crystal structure can be expected to be one feasible way to design new IR NLO candidates with excellent performance.

A series of M3PS4 (M = Ag, Cu and Ag/Cu) thiophosphates with diamond-like structures exhibiting large second harmonic generation responses and moderate ion conductivities

Diamond-like thiophosphates exhibiting large second harmonic generation responses and moderate ion conductivities were systematically studied.