Silicon materials play a key role in many technologically relevant fields, ranging from the electronic to the photovoltaic industry. A systematic search for silicon allotropes was performed by employing a modified ab initio minima hopping crystal structure prediction method. The algorithm was optimized to specifically investigate the hitherto barely explored low-density regime of the silicon phase diagram by imitating the guest-host concept of clathrate compounds. In total 44 metastable phases are presented, of which 11 exhibit direct or quasi-direct band-gaps in the range of $\approx$1.0-1.8 eV, close to the optimal Shockley-Queisser limit of $\approx$1.4 eV, with a stronger overlap of the absorption spectra with the solar spectrum compared to conventional diamond silicon. Due to the structural resemblance to known clathrate compounds it is expected that the predicted phases can be synthesized.
We report the prediction of metallic quasione-dimensional $sp^{3}$-hybridized silicon allotropes in the form of prismanes. Silicon prismanes or polysilaprismanes are the silicon nanotubes of a special type constructed from the dehydrogenated molecules of cyclosilanes (silicon rings). By means of density functional theory the electronic, geometry, energy, and some mechanical properties of these tubes were investigated. Our results show that silicon polyprismanes are thermodynamically stable compounds, and the character of the energy spectrum, as well as the behavior of transmission function nea…
Novel extended networks of C8, Si8 and silicon carbide Si4C4 are proposed based on crystal chemistry rationale and optimized structures to ground state energies and derived physical properties within the density functional theory (DFT). The two carbon and silicon allotropes and the silicon carbide belong to primitive tetragonal space group P-4m2 Number 115. C8 allotrope structure made of corner sharing C4 and Si4 tetrahedra is illustrated by charge density projections exhibiting sp3 like carbon hybridization. From careful symmetry analysis, Symmetry analysis of C8 indicated that it is another …
Silicon and germanium are the well-known materials used to manufacture electronic devices for the integrated circuits but they themselves are not considered as promising options for interconnecting the devices due to their semiconducting nature. We have discovered that both Si and Ge atoms can form unexpected metallic monolayer structures which are more stable than the extensively studied semimetallic silicene and germanene, respectively. More importantly, the newly discovered two-dimensional allotropes of Si and Ge have Fermi velocities superior to the Dirac fermions in graphene, indicating t…
Silicon in a cubic diamond structure currently plays a significant role in the photovoltaic industry. However, the intrinsic band structures of crystalline silicon restrict its sunlight conversion efficiency. Recently, a clathrate-like Si-24 has been successfully synthesized, which has a quasi-direct bandgap and sheds light on silicon-based photovoltaics. Here, we proposed a two-step crystal structure search method based on first-principles calculations and explored silicon clathrate structures extensively. First, the guest-host compounds were searched at high pressure, and then, the porous gu…
Computational searching and screening of new functional materials exploiting earth abundant elements can accelerate developments of their energy applications. Based on a state-of-the-art materials search algorithm and ab initio calculations, we demonstrate a recently suggested stable silicon oxide with a layered structure (Si$_{3}$O) as an ideal photovoltaic material. With many-body first-principles approaches, the monolayer and layered bulk of Si$_{3}$O show direct quasiparticle gaps of 1.85 eV and 1.25 eV, respectively, while an optical gap of about 1.2 eV is nearly independent of the number…
The Effect of Hybrid Photovoltaic Thermal Device Operating Conditions on Intrinsic Layer Thickness Optimization of Hydrogenated Amorphous Silicon Solar Cells
Confined microexplosions induced in silicon by powerful ultrashort laser pulses can lead to new Si phases. Some of these have not previously been observed via near-equilibrium compression of silicon. In this study, confocal Raman micro-spectroscopy and Raman imaging of arrays of microexplosions have been conducted to search for Raman signatures of these novel allotropes of silicon. A microexplosion is generated at the interface between a thick silicon dioxide confinement layer and underlying silicon. It is characterised by a void at the interface above a region of compressed silicon. Raman dat…
A series of carbon allotropes with novel optoelectronic and rich topological properties is predicted by systematic first-principles calculations. These fascinating carbon allotropes can be derived by inserting acetylenic linkages (-C$\equiv$C-) into graphite, hence they are termed as grapheaynes. Grapheaynes possess two different space groups, $P$2/$m$ or $C$2/$m$, and contain simultaneously the $sp$, $sp^2$, and $sp^3$ chemical bonds. They have formation energies lower than the already experimentally synthesized graphdiyne and other theoretically predicted carbon allotropes with acetylenic li…
Graphene-silicon Schottky junction (GSJ) which has the potential for large-scale manufacturing and integration can bring new opportunities to Schottky solar cells for photovoltaic (PV) power conversion. However, the essential power conversion limitation for these devices lies in the small open-circuit voltage ($V_{oc}$), which depends on the Schottky barrier height (SBH). In this study, we introduce an electromechanical method based on the flexoelectric effect to enhance the PV efficiency in GSJ. By atomic force microscope (AFM) tip-based indentation and in situ current measurement, the curren…
Owing to the natural compatibility with current semiconductor industry, silicon allotropes with diverse structural and electronic properties provide promising platforms for the next-generation Si-based devices. After screening 230 all-silicon crystals in the zeolite frameworks by first-principles calculations, we disclose two structurally stable Si allotropes (AHT-Si24 and VFI-Si36) containing open channels as topological node-line semimetals with Dirac nodal points forming a nodal loop in the kz=0 plane of Brillouin zone. Interestingly, their nodal loops protected by inversion and time-revers…
Amorphous hydrogenated silicon (a-Si:H) is an important material for surface defect passivation of photovoltaic silicon (Si) wafers in order to reduce their recombination losses. The material is however unstable with regards to hydrogen (H) desorption at elevated temperatures, which can be an issue during processing and device manufacturing. In this work we determine the temperature stability of a-Si:H by structural characterization of a-Si:H/Si bilayers with neutron- (NR) and X-ray reflectometry (XRR) combined with photoconductance measurements yielding the minority carrer lifetime. The neutr…
Here we report the development of high-efficiency microscale GaAs laser power converters, and their successful transfer printing onto silicon substrates, presenting a unique, high power, low-cost and integrated power supply solution for implantable electronics, autonomous systems and internet of things applications. We present 300 μm diameter single-junction GaAs laser power converters and successfully demonstrate the transfer printing of these devices to silicon using a PDMS stamp, achieving optical power conversion efficiencies of 48% and 49% under 35 and 71 W/cm2 808 nm laser illumination r…
Since the discovery of graphene, intensive efforts have been made in search of novel two-dimensional (2D) materials. Decreasing the materials dimensionality to their ultimate thinness is a promising route to unveil new physical phenomena, and potentially improve the performance of devices. Among recent 2D materials, analogs of graphene, the group IV elements have attracted much attention for their unexpected and tunable physical properties. Depending on the growth conditions and substrates, several structures of silicene, germanene, and stanene can be formed. Here, we report the synthesis of a…
Upconversion of sub-band-gap photons constitutes a promising way for improving the efficiency of silicon-based solar cells beyond the Shockley-Queisser limit. 1500 to 980 nm upconversion by trivalent erbium ions is well-suited for this purpose, but the small absorption cross section hinders real-world applications. We employ tailored gold nanostructures to vastly improve the upconversion efficiency in erbium-doped TiO$_2$ thin films. The nanostructures are found using topology optimization and parameter optimization and fabricated by electron beam lithography. In qualitative agreement with a t…
Moisture in the form of humidity has a significant impact on the operation of photovoltaic (PV) cells and panels. Moisture is often diffuse through the encapsulant film (Ethylene Vynil Acetate (EVA), PVB, PVF, PMMA) or the breathable back-sheet. Moisture is known to accelerate the degradation and reduce the performance of a PV while operating in a wet environment. SCAPS 1 D is widely used to simulate and estimate the operation of PV. In this work, we showed the effect of moisture on the operation and performance of a PV, made from monocrystalline silicon. Namely, the influence of defects and i…
Silicene, the two-dimensional allotrope of silicon, is predicted to exist in a low-buckled honeycomb lattice, characterized by semimetallic electronic bands with graphenelike energy-momentum dispersions around the Fermi level (represented by touching Dirac cones). Single layers of silicene are mostly synthesized by depositing silicon on top of silver, where, however, the different phases observed to date are so strongly hybridized with the substrate that not only the Dirac cones, but also the whole valence and conduction states of ideal silicene appear to be lost. Here, we provide evidence tha…
Circularity in Perovskite-Based Tandem Photovoltaics for Terawatt-Scale Deployment
University of Toulouse, Toulouse INP, CNRS, LGC（图卢兹大学）；Inorganic Chemistry Laboratory, University of Oxford（牛津大学无机化学实验室）；Department of Mechanical Engineering, University of Bath（巴斯大学机械工程系）；Environment and Sustainability Institute, University of Exeter（埃克塞特大学环境与可持续发展研究所）；Department of Mechanical and Energy Engineering, College of Engineering, Imam Abdulrahman Bin Faisal University（伊玛姆阿卜杜勒拉赫曼·本·费萨尔大学工程学院机械与能源工程系）；Department of Materials, University of Oxford（牛津大学材料系）
Molecular dynamics simulations play an important role in studying heat transport in complex materials. The lattice thermal conductivity can be computed either using the Green-Kubo formula in equilibrium MD (EMD) simulations or using Fourier's law in nonequilibrium MD (NEMD) simulations. These two methods have not been systematically compared for materials with different dimensions and inconsistencies between them have been occasionally reported in the literature. Here we give an in-depth comparison of them in terms of heat transport in three allotropes of Si: three dimensional bulk silicon, tw…
Harnessing low energy photons is of paramount importance for multi-junction high efficiency solar cells as well as for thermo-photovoltaic applications. However, semiconductor absorbers with bandgap lower than 0.8 eV have been limited to III-V (InGaAs) or IV (Ge) semiconductors that are characterized by high manufacturing costs and complicated lattice matching requirements in their growth and integration with the higher bandgap cells. Here, we have developed solution processed low bandgap photovoltaic devices based on PbS colloidal quantum dots (CQDs) with a bandgap of 0.7 eV suited for both t…
Lead-halide perovskites have demonstrated astonishing increases in power conversion efficiency in photovoltaics over the last decade. The most efficient perovskite devices now outperform industry-standard multi-crystalline silicon solar cells, despite the fact that perovskites are typically grown at low temperature using simple solution-based methods. However, the toxicity of lead and its ready solubility in water are concerns for widespread implementation. These challenges, alongside the many successes of the perovskites, have motivated significant efforts across multiple disciplines to find …
Hybrid organic-inorganic halide perovskites have emerged as a disruptive new class of materials, exhibiting optimum properties for a broad range of optoelectronic applications, most notably for photovoltaics. The first report of highly efficient organic-inorganic perovskite solar cells in 2012 marked a new era for photovoltaics research, reporting a power conversion efficiency of over 10%. Only five years after this discovery, perovskite photovoltaic devices have reached a certified efficiency of 22.7%, making them the first solution processable technology to surpass thin film and multi-crysta…
Using machine learning (ML) approach, we unearthed a new III-V semiconducting material having an optimal bandgap for high efficient photovoltaics with the chemical composition of Gallium-Boron-Phosphide(GaBP$_2$, space group: Pna2$_1$). ML predictions are further validated by state of the art ab-initio density functional theory (DFT) simulations. The stoichiometric Heyd-Scuseria-Ernzerhof (HSE) bandgap of GaBP$_2$ is noted to 1.65 eV, a close ideal value (1.4-1.5 eV) to reach the theoretical Queisser-Shockley limit. The calculated electron mobility is similar to that of silicon. Unlike perovsk…
