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Despite the conventional view of liquid aluminum (l-Al) as a simple metal governed by the free-electron model, it exhibits unique bonding characteristics. This study uncovers a gradual transition from free electron to electride behavior in l-Al at high pressure and temperature, forming a type of two-component liquid where atomic and electride states coexist. The proportion of electride increases with pressure and temperature until reaching saturation, leading to notable changes in the pair-correlation function and coordination number of l-Al at saturation pressure. Furthermore, this electride transition was found to profoundly impact the thermodynamic and dynamic properties, as evidenced by anomalous crossovers in the isothermal bulk modulus, thermal expansivity, heat capacity, sound speed, and self-diffusion coefficient correlated with varying pressure and temperature. The finding of the anomalous behavior of l-Al described in this work will deepen our understanding of the electronic structure and also lay ground work for interpreting and predicting new physical and chemical behavior under extreme conditions. [ABSTRACT FROM AUTHOR]

Perovskite‐inspired materials (PIMs) are potential alternatives to lead halide perovskites, as they not only inherit the benign optoelectronic properties but also diminish the stability and toxicity issues of lead halide perovskites. As a newly discovered PIM, Cu2AgBiI6 has exhibited promising potential for photovoltaic applications. However, studies on its fundamental properties related to photovoltaic performance are scarce, particularly from a theoretical perspective. Herein, the effective lifetime of nonequilibrium carriers (photo‐excited charge carriers) is systematically investigated, a critical property affecting the photovoltaic performance of Cu2AgBiI6, based on the nonadiabatic molecular dynamics simulations. It is found that under the standard solar spectrum illumination, the dominant recombination mechanism affecting the effective lifetime can be band‐to‐band nonradiative decay, band‐to‐band radiative decay, or Shockey–Read–Hall defect‐assisted decay. The specific mechanism is highly dependent on the radiative recombination coefficient and the density of defect recombination levels. The effective lifetime can vary from 0.1 ms to 10 ns. When considering different illumination conditions (generation rates), Auger decay can also become the dominant recombination mechanism, with the effective lifetime varying from 0.1 s to 0.1 ns. These findings can be vital for further experimental researches aimed at enhancing the power conversion efficiency of Cu2AgBiI6‐based solar devices. [ABSTRACT FROM AUTHOR]

In lead–halide perovskites, antibonding states at the valence band maximum (VBM)—the result of Pb 6s-I 5p coupling—enable defect-tolerant properties; however, questions surrounding stability, and a reliance on lead, remain challenges for perovskite solar cells. Here, we report that binary GeSe has a perovskite-like antibonding VBM arising from Ge 4s-Se 4p coupling; and that it exhibits similarly shallow bulk defects combined with high stability. We find that the deep defect density in bulk GeSe is ~1012 cm−3. We devise therefore a surface passivation strategy, and find that the resulting GeSe solar cells achieve a certified power conversion efficiency of 5.2%, 3.7 times higher than the best previously-reported GeSe photovoltaics. Unencapsulated devices show no efficiency loss after 12 months of storage in ambient conditions; 1100 hours under maximum power point tracking; a total ultraviolet irradiation dosage of 15 kWh m−2; and 60 thermal cycles from −40 to 85 °C. Perovskite-like antibonding VBM electronic structure is predicted to result in defect-tolerant materials. Here, the authors investigate GeSe with antibonding VBM from Ge 4s-Se 4p coupling, and a certified 5.2% PCE is obtained with high stability due to its strong covalent bonding. [ABSTRACT FROM AUTHOR]

Through first‐principles calculations, it is found that two lattice‐matched halide double‐perovskites, Cs2NaBiBr6 and Cs2AgBiBr6, have a type‐I band alignment and can form highly miscible alloys in which the disordering makes the bandgaps become direct and activates the direct transition from the valence to conduction band edge, leading to a strong optical absorption and high radiative recombination rate. The bandgaps of the alloys are tunable in a wide range of 1.93–3.24 eV, while the lattice constants remain unchanged. This advantage inspires the design of a coherent crystalline matrix based on Cs2(Na,Ag)BiBr6 alloys, in which the Ag‐rich and narrower‐bandgap regions are embedded in the Na‐rich and wide‐bandgap region with lattice‐matched and coherent interfaces. The type‐I band alignment drives the photogenerated excitons into the narrower‐bandgap Ag‐rich regions, so the regions become light‐emitting centers with a high photoluminescence quantum yield (PLQY). The bandgaps of the Ag‐rich regions are tunable, so the color of emitted light can be adjusted, making a broadband emission possible. Such kind of coherent crystalline matrix with high‐PLQY and broadband emission can also be fabricated based on the alloys of other lattice‐matched halide double‐perovskites, demonstrating the flexibility of band structure engineering in the coherent heterostructures of various halide double‐perovskites. [ABSTRACT FROM AUTHOR]

The photovoltaic efficiency increase in Sb2S3‐based solar cells has stagnated for 5 years since the highest efficiency of 7.5% was achieved in 2014. One important bottleneck is the high electrical resistivity of Sb2S3. The first‐principle calculations reveal that the high‐resistivity results from the compensation between the intrinsic donor VS and acceptors VSb, SbS, and SSb which have comparably high concentration (low formation energy). The compensation also limits the improvement of conductivity through direct extrinsic doping. Further calculations of O dopants show that OS has low formation energy, so the dominant intrinsic donor VS can be passivated by O and thus the p‐type doping limit imposed by VS can be overcome. Meanwhile, other p‐type limiting and recombination‐center donor defects can be suppressed under the S‐rich condition, which explains why the highest efficiency is achieved in O‐doped Sb2S3 after sulfurization. Given the unexpected beneficial effects of O doping and sulfurization, a two‐step doping strategy is proposed for overcoming the efficiency bottleneck: 1) use O to passivate the VS and S‐rich condition to suppress other detrimental defects, making p‐type doping feasible and minority carrier lifetime long; 2) introduce other p‐type dopants to increase hole carrier concentration. [ABSTRACT FROM AUTHOR]

NaSbSe2 has recently shown great potential to be a light-absorber semiconductor in thin-film solar cells. Our first-principles calculations show that NaSbSe2 has a quasi-direct bandgap (1.11 eV indirect vs 1.18 eV direct gap), which is beneficial for increasing the lifetime of minority carriers. The optical absorption coefficient is high (exceeding 10−4 cm−1 for visible light) because of the direct band-edge transition from the (Sb-5s/5p + Se-4p) valence band to (Sb-5p + Se-4p) conduction band. The formation of the dominant acceptor defects such as NaSb, VNa, and VSb makes it difficult to dope NaSbSe2 to n-type, and thus, only the intrinsic p-type conductivity has been observed. Se-rich conditions are found to produce high concentration of hole carriers and low concentration of recombination-center defects, so we propose that the Se-rich conditions should be adopted for fabricating high efficiency NaSbSe2 solar cells. Furthermore, the mixed-anion NaSb(S,Se)2 alloys are predicted to be highly miscible with a low formation enthalpy and a low miscibility temperature (below room temperature), and their bandgaps can be tuned almost linearly from 1.1 to 1.6 eV, covering the optimal bandgap range for single-junction solar cells. Therefore, we propose that alloying provides a promising method for optimizing the performance of NaSbSe2-based solar cells. [ABSTRACT FROM AUTHOR]

Bi2S3 has attracted extensive attention recently as a light-absorber, sensitizer or electron acceptor material in various solar cells. Using first-principles calculations, we find that the photovoltaic efficiency of Bi2S3 solar cells is limited by its intrinsic point defects, i.e., both S vacancy and S interstitial can have high concentration and produce deep defect levels in the bandgap, leading to non-radiative recombination of electron–hole carriers and reduced minority carrier lifetime. Unexpectedly most of the intrinsic defects in Bi2S3, including even the S interstitial, act as donor defects, explaining the observed n-type conductivity and also causing the high p-type conductivity impossible thermodynamically. Doping in Bi2S3 by a series of extrinsic elements is studied, showing that most of the dopant elements such as Cu, Br and Cl make the material even more n-type and only Pb doping makes it weakly p-type. Based on this, we propose that the surface region of n-type Bi2S3 nanocrystals in p-PbS/n-Bi2S3 nano-heterojunction solar cells may be type-inverted into p-type due to Pb doping, with a buried p–n junction formed in the Bi2S3 nanocrystals, which provides a new explanation to the longer carrier lifetime and higher efficiency [Nat. Photonics, 6, 529 (2012)]. Considering the relatively low conduction band and high n-type conductivity, we predict that Cu, Br and Cl doped Bi2S3 may be an ideal n-type electron acceptor or counter electrode material, while the performance of Bi2S3 as a light-absorber or sensitizer material is intrinsically limited. [ABSTRACT FROM AUTHOR]

As a new member of 2D materials, GeSe has attracted considerable attention recently due to its fascinating in‐plane anisotropic vibrational, electrical, and optical properties originating from the low‐symmetry crystal structure. Among these anisotropic properties, the anisotropic optical property, as a new degree of freedom to manipulate optoelectronic properties in 2D materials, is of great importance for practical applications. However, the fundamental understanding of the optical anisotropy of GeSe is still under exploration, severely restricting its utility in polarization‐sensitive optical systems. Here, a systematic study about the in‐plane optical anisotropy of GeSe is reported, including its anisotropic optical absorption, reflection, extinction, and refraction. The anisotropic band structure of GeSe is experimentally observed for the first time through angle‐resolved photoemission spectroscopy, explaining the origin of the optical anisotropy. The anisotropic reflection and refraction of GeSe are further directly visualized through the angle‐dependent optical contrast of GeSe flakes by azimuth‐dependent reflectance difference microscopy and polarization‐resolved optical microscopy, respectively. Finally, GeSe‐based photodetectors exhibit a polarization‐sensitive photoresponsivity due to the intrinsic linear dichroism. This study provides fundamental information for the optical anisotropy of GeSe, forcefully stimulating the exploration of novel GeSe‐based optical and optoelectronic applications. In‐plane optical anisotropy of GeSe is systematically studied by angle‐resolved photoemission spectroscopy, azimuth‐dependent reflectance difference microscopy, and polarization‐resolved optical microscopy, thus providing fundamental information for the optical anisotropy of GeSe and stimulating the exploration of novel GeSe‐based optical and optoelectronic applications. [ABSTRACT FROM AUTHOR]