In this paper, a dual-band tunable perfect plasmon absorber based on graphene split-ring-resonator is proposed. The device is composed of resonant ring graphene with an open top layer, a thick PMMA spacer layer and a Cu substrate mirror layer, which has simple structural characteristics. By FDTD simulation method, the numerical results show that perfect absorption is achieved at resonance wavelengths lambda(A) = 39.30 mu m and lambda(B) = 62.00 mu m, and the absorption rates are 99.55% and 99.64%, respectively. By adjusting the geometric parameters of graphene array, changing the structural period P and PMMA dielectric thickness, the absorber can achieve perfect absorption. In addition, the resonance wavelength and absorption peak of the absorber can be effectively tuned by controlling the chemical potential, relaxation time and dielectric constant inside the absorber. At last, we exposed the structure to different environmental refractive indices, and calculated the corresponding maximum sensitivities of the two resonant modes as SA = 13.82 mu m/RIU and S-B = 21.47 mu m/RIU. The maximum figure of merit are FOM1 = 4.4870 RIU-1 and FOM2 = 3.5148 RIU-1 respectively. Therefore, the design of graphenebased tunable perfect metamaterial absorber proposed in this study can be applied to photodetectors, sensors and other fields.

In this work, we develop a radio-frequency plasma-enhanced horizontal tube furnace deposition system to directly grow graphene nanowalls (GNWs) on inverted pyramid (IP) silicon without using catalysts and fabricate GNWs/IP silicon Schottky junction solar cells. The morphology, microstructure, and optical and electrical properties of the synthesized GNWs and IP silicon are investigated. It is shown that GNWs are distributed on the whole surface of the IP silicon and feature an outstanding electrode network. Moreover, in situ optical emission spectroscopy measurement is carried out to investigate the growth process and chemical reaction mechanism of GNWs under the plasma-based process. Due to the excellent light-trapping structure of IP silicon and outstanding electrode network of GNWs, the photovoltaic conversion efficiency (PCE) of the pristine GNWs/IP Si solar cells can reach up to 4.05% via controlling the growth time of GNWs. A PCE of 7.2% can be achieved for the GNWs/IP Si solar cells by combining HNO3 p-doping treatment and spin-coating TiO2 as an antireflective layer. This work plays a vital role in the development of a simple and advanced process for the realization of high-efficiency graphene-based solar cells.

In this paper, using the surface plasmon and Fabry–Pérot (FP) cavity, the design of a symmetric silicon grating absorber is proposed. The time-domain finite difference method is used for simulation calculations. The basic unit structure is a dielectric grating composed of silicon dioxide, metal and silicon. Through the adjustment of geometric parameters, we have achieved the best of the symmetric silicon grating absorber. A narrowband absorption peak with an absorption rate greater than 99% is generated in the 3000–5000 nm optical band, and the wavelength of the absorption peak is λ = 3750 nm. The physical absorption mechanism is that silicon light generates surface plasmon waves under the interaction with incident light, and the electromagnetic field coupling of surface plasmon waves and light causes surface plasmon resonance, thereby exciting strong light response modulation. We also explore the influence of geometric parameters and polarization angle on the performance of silicon grating absorbers. Finally, we systematically study the refractive index sensitivity of these structures. These structures can be widely used in optical filtering, spectral sensing, gas detection and other fields.

This paper proposes a square ring-shaped triple-band perfect absorber based on graphene with silicon as the substrate, gold as the reflector and a thin dielectric layer of silicon dioxide. After simulation by the FDTD method, the numerical results show that the absorption spectrum based on the periodic array structure of graphene exhibits three perfect absorption peaks in the terahertz band, corresponding to 25.53 μm, 36.44 μm and 53.44 μm, respectively, and they all reach 99% absorption rate. By changing the gate voltage, the material parameters of graphene can be easily adjusted, so as to achieve dynamic control of the absorption characteristics of the absorber. Due to the high symmetry of the structure, it has a good angular polarization tolerance in the far infrared band. In addition, the obvious spectral shift caused by the change of surrounding environment refractive index and the values of sensitivity (S) and figure of merit (FOM) are all indicates that our absorber has certain application prospects in the field of sensing. Furthermore, our absorber has shown great application potential in light detection in infrared and terahertz band as a consequence of the strong tunability.

To date, almost all reported graphene nanowalls (GNWs)/Si solar cells are fabricated through the direct deposition of GNWs on the silicon wafer. In this work, we report a polymer-free transfer method of GNWs grown on the copper foil for the fabrication of GNWs/Si solar cells. This allows us to further improve the photovoltaic performance of the solar cells by means of interface engineering. An optimized photovoltaic conversion efficiency (PCE) of the as-fabricated GNWs/Si solar cell can reach up to 4.99%. Furthermore, the PCE of the device is further improved by introducing the spiro-OMeTAD thin film as an interface layer, which serves as an electron-blocking and hole-transporting layer through tuning the band structure of the solar cells. Without any chemical doping and anti-reflecting coating, the maximum PCE of 8.27% has been achieved for the GNWs/spiro-OMeTAD/Si solar cell through optimizing the dopant content and the thickness of the spiro-OMeTAD thin film. We believe that our study indicates a new route for the fabrication of high-efficiency, low-cost GNWs/Si Schottky heterojunction solar cells without the need for chemical doping of the GNWs.

For a thorough understanding of graphene/GaAs heterojunction solar cells, the effect of the graphene work function, absorption loss, density of interface states, as well as the incorporation of an AlxGa1-xAs (0 <= x <= 1) buffer layer on the performance of graphene/GaAs heterojunction solar cells was investigated via AFORS-HET simulation software. It is demonstrated that graphene with a work function of approximately 5 eV favors the efficiency improvement. The absorption loss is also an unnegligible factor for the optimization of the graphene work function. The density of interface states can significantly affect the carrier recombination at the heterojunction interface between graphene and GaAs and the corresponding photovoltaic performance. In addition, the work function of a back electrode should also be taken into account for selecting a back electrode material due to its significant influence on the carrier transportation and collection. Furthermore, when an AlxGa1-xAs (x = 0.2) buffer layer was introduced to this heterojunction interface, an enhanced photovoltaic conversion efficiency of 24.78% can be achieved. Finally, a comparison among simulation and experimental data for the graphene/GaAs heterojunction solar cells is presented. This study indicates the great potential of graphene/GaAs heterojunction for the application in high-efficiency solar cells.

A conversion efficiency of 20.23% of heterojunction with intrinsic thin layer (HIT) solar cell on 156 mm × 156 mm metallurgical Si wafer has been obtained. Applying AFORS-HET software simulation, HIT solar cell with metallurgical Si was investigated with regard to impurity concentration, compensation level, and their impacts on cell performance. It is known that a small amount of impurity in metallurgical Si materials is not harmful to solar cell properties.

In this work, we develop a simple customized radio-frequency plasma-enhanced horizontal tube furnace deposition system to directly grow high-quality ZnO nanorod arrays on zinc films and investigate their application as an antireflective layer in n + pp + monocrystalline silicon (c-Si) solar cells. Field emission scanning electron microscope, X-ray diffractometer, and transmission electron microscope studies reveal that ZnO nanorod arrays feature a perfect crystalline wurtzite structure and grow preferentially along [0001] direction. The antireflective performance of ZnO nanorod arrays is confirmed by Fresnel coefficient matrix method and MATLAB software calculation. Furthermore, PC1D simulation demonstrates that the photovoltaic property for c-Si solar cells of the pyramid-textured front surface using ZnO nanorod arrays as an antireflective layer is much better than that for the other three types of c-Si solar cells (i.e., c-Si solar cells of the pyramid-textured front surface without using any antireflective layer, c-Si solar cells of the planar front surface using ZnO nanorod arrays as an antireflective layer, as well as c-Si solar cells of the planar front surface without using any antireflective layer). In particular, the photovoltaic conversion efficiency of 20.23% has been achieved for c-Si solar cells of the pyramid-textured front surface using ZnO nanorod arrays as an antireflective layer. This work is highly relevant to the development of an advanced process for the realization of high-efficiency, low-cost, and stable solar cells.

Aluminum-alloyed back-junction is a novel concept for low-cost and industrially feasible n-type silicon solar cells. In this paper, we fabricated industrially high-efficiency solar cells based on both uncompensated and compensated n-type silicon. Moreover, we measured the impact of temperature on the photovoltaic performance of aluminum-alloyed back-junction n-type silicon solar cells. Compared with conventional front-junction solar cells, the back-junction silicon solar cells have a lower absolute temperature coefficient especially for moderate carrier diffusion lengths which is attributed to distinctive spectral response, stronger dependence on carrier diffusion lengths, and incomplete ionization of aluminum. In addition, the lowest absolute temperature coefficient is obtained on this type of aluminum-alloyed back-junction solar cell when the compensated silicon is used as the base layer. These results suggest that aluminum-alloyed back-junction solar cells especially based on the compensated silicon can generate more electricity at a high temperature, and therefore, as a cost-effective production of silicon solar cells, this type of solar cells have a very good potential for actual outdoor application. This work is highly relevant to the development of an advanced process for the achievement of low-cost, high-efficiency, commercially viable silicon-based solar cells.

Vertically-oriented graphene nanowalls (VGNWs) have been successfully synthesized under different experimental conditions (such as flow rate of argon, growth temperature, plasma power as well as deposition time) on copper foils in the reactive methane and argon environment using a capacitively coupled plasma-enhanced horizontal tube furnace deposition system. It is shown that the morphology and structure of VGNWs can be effectively tailored by experimental conditions. Furthermore, the growth mechanism of VGNWs produced in the plasma-based approach has been investigated. The synthesized VGNWs are used as anode materials in Li-ion batteries and the batteries show outstanding cycle efficiency (similar to 99%). The specific capacity of coin-type cells can be improved by adjusting the experimental parameters and reaches 400 mAh g(-1) in the first charge-discharge cycle. This work is particularly important for the development of an advanced process for the synthesis and application of carbon-based nanomaterials.

A novel green phosphor, Sr2MgB2O6:Tb3+,Li+ for white light-emitting diodes was prepared by solid-state reactions, and its structure and luminescence properties were investigated. The excitation and emission spectra indicated that this as-prepared phosphor could be effectively excited by ultraviolet 368 nm, and exhibited bright green emission centered at 545 nm corresponding to the 5D4→7F5 transition. 9 mol.% of Tb3+ was shown to be optimal. Good green emissions with the CIE chromaticity coordinates (0.262, 0.583) could be achieved. Furthermore, the integrated emission intensity of Sr2MgB2O6:0.09Tb3+,0.09Li+ phosphor decreased continuously to 72.1% at 300 °C with increasing temperature, and the activation energy of thermal quenching (Ea) was calculated to be 0.175 eV, moreover, the quantum yield excited by 368 nm was measured as 11.1%. A green emission LED was made by coating Sr2MgB2O6:0.09Tb3+,0.09Li+ phosphor on a NUV (365-370 nm) chip. Our results showed that Sr2MgB2O6:Tb3+,Li+ is a kind of potential green-emitting phosphor and features good thermal stability.

N-type compensated silicon shows unusual distribution of resistivity as crystal grows compared to the n-type uncompensated silicon. In this paper, evolutions of resistivities with varied concentrations of boron and varied starting resistivities of the n-type silicon are intensively calculated. Moreover, reduction of carrier mobility is taken into account by Schindler's modified model of carrier mobility for the calculation of resistivity of the compensated silicon. As for substrates of solar cells, optimized starting resistivity and corresponding concentration of boron are suggested for better uniformity of resistivity and higher yield (fraction with rho > 0.5 Omega center dot cm) of the n-type compensated Cz crystal rod. A two-step growth method is investigated to obtain better uniformity of resistivity of crystal rod, and this method is very practical especially for the n-type compensated silicon. Regarding the carrier lifetime, the recombination by shallow energy-level dopants is taken into account for the compensated silicon, and evolution of carrier lifetime is simulated by considering all main recombination centers which agrees well with our measured carrier lifetimes as crystal grows. The n-type compensated silicon shows a larger reduction of carrier lifetime compared to the uncompensated silicon at the beginning of crystal growth, and recombination with a oxygen-related deep defect is sufficient to describe the reduction of degraded lifetime. Finally, standard heterojunction with intrinsic thin-layer ( HIT) solar cells are made with substrates from the n-type compensated silicon rod, and a high efficiency of 22.1% is obtained with a high concentration (0.8 x 10(16) cm(-3)) of boron in the n-type compensated silicon feedstock. However, experimental efficiencies of HIT solar cells based on the n-type compensated silicon show an average reduction of 4% along with the crystal length compared to the uncompensated silicon. The obtained results enrich our knowledge on the n-type compensated silicon and contribute to the development of n-type compensated silicon-based solar cells for commercial application.

Research on electrical properties of the compensated silicon is very crucial for understanding the doping layer and compensated substrates of solar cells. Regarding the fact that there are still inadequate experimental data of carrier mobility on the n-type compensated silicon, hence in this paper, both majority electron and minority hole mobilities measured on the n-type compensated solar-grade silicon substrates are presented. Prediction models of carrier mobility are essential for material characterization and device (e.g. solar cells) simulation. However, as prediction models of carrier mobility are commonly established based on the uncompensated silicon, large deviations of carrier mobility have been observed on the compensated silicon. In this work, the standard Klaassen’s model and optimized model for the compensated silicon by Schindler et al. are reviewed and compared to measured carrier mobilities. Moreover, the factors that lead to deviations of Klaassen’s model on the n-type compensated silicon are critically discussed, and then we propose an optimized model for prediction of carrier mobility in the compensated silicon. This model can also be extended to both majority and minority carrier mobilities in p- and n-type compensated silicon and fits well with previous published data as well as carrier mobility data presented here. In addition, evolutions of majority electron and minority hole mobilities as crystal grows are also simulated for n-type compensated Czochralski silicon which agrees well with our measured results.

A YAG continue-wave laser has been used to refine the surface of silicon wafers in this study. During laser scanning, the irradiated region of the surface of the wafer experienced melting and subsequent recrystallization, which results in a redistribution of metal impurities in the molten pool along the depth direction. Cross-sectional micrographs of irradiated wafers have a clear boundary, which confirms the process of recrystallization, and the depth of molten region depends on the scanning parameters and the size of wafer. Secondary ion mass spectrometry measurements have been carried out to characterize the concentration of metal impurities. After redistribution of metal impurities, a final relative purity region was formed close to the surface. SIMS measurements demonstrate that the metal impurity concentration of the purity region has significantly reduced. The mechanism of the redistribution process of metal impurities in the molten pool has been qualitatively analyzed. All of the experimental results support that the CW laser scanning technology can effectively refine the specific surfaces of silicon wafers, and this technology has a great potential in the field of solar cells.

Ribbon silicon material is specially designed for solar cell wafers. In this paper, a novel ribbon silicon material “dipping method” has been designed in order to lower the cost of solar cell. The principle and procedure of dipping method were described. In addition, the diffusion of impurities in the silicon wafer and its influence on the efficiency of solar cells were investigated. The photovoltaic performance of polycrystalline silicon solar cells which were based on the metallurgical grade silicon substrate with the thickness of 600μm, was simulated by AMPS1-D software. And some import parameters were obtained including I-V characteristic, 17.004% conversion efficiency. This artic is provided theoretical support to the industrial production of solar cells by dipping method, and it will open a new road to production low cost solar cell.

In this paper, we investigated the characterization of a gallium co-doping multicrystalline silicon ingot made of solar-grade silicon purified by metallurgical route. It is shown that the addition of gallium yields a fully p-type ingot and resistivity distribution in the range from 1.2 Ω.cm to1.7 Ω.cm along the full ingot height. Minority carrier lifetime measurements indicate that this material is suitable for the production of solar cells with comparable efficiencies to standard material. In addition, gallium addition in compensated silicon during ingot casting is proved to be very prospective for controlling the resistivity and increasing material yield of ingot.

Solar cell is one of most important renewable energy. But now it is not be widely used because of its high cost compared with traditional resource. Ribbon silicon is one new low cost solar cell material avoiding ingot casting and slicing. It is a promising silicon wafer fabrication technology alternative to traditional ingot casting and slicing. Using ribbon silicon can make solar cell production cost greatly reduced. In this paper EFG, String Ribbon and a novel silicon wafer are discussed.

With mc-silicon (multi-crystalline silicon) being the most favorable feedstock for solar cell, germanium was reported to be a promising dopant to improve the quality of silicon crystal growth. In this paper, we investigated the feasibility of germanium doping for industrial scale production. A homogeneously distribution of germanium across usable section is presented, and subsequently we optimized our recipe for better controlling it. Sopori etched pits were utilized to reveal dislocations in silicon wafers, and we found a reduced dislocations density in germanium doped samples. Carbon and oxygen are two inevitable significant impurities during silicon ingot casting. In this paper, experimental results showed the impact of carbon on minority charge carrier lifetime and on interstitial oxygen. In addition, Isostatic pressing method is proved to be very prospective for recycling quartz crucibles.