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Laser doping (LD) of born‐doped Si paste (Si paste) is a potential boron‐doping approach for advanced solar cells. It is aimed to develop a top‐hat LD instead of a Gaussian LD and a rear‐side polishing process to fabricate P++ local contacts for improved passivated emitter and rear contact (i‐PERC) cells. With the help of vision alignment, LD is conducted on a dashed line pattern of printed Si paste, which decreases the consumption of paste. The variations of boron content in Si paste and the laser pulse energy density can help customize the doping profile. The predicted result of the boron LD profile is a peak dopant density of 2 × 1019 atoms cm−3 and a dopant depth of over 4.0 μm. When higher firing temperature, it can obtain thicker localized back surface field of over 7 μm, since the gradient of the residual Si concentration at the Al/Si interface can suppress the formation of voids. The overall increment in fill factor, short‐circuit current, and open‐circuit voltage enhances the average efficiency by 0.11% for i‐PERC cells and 0.09% for i‐bifacial PERC cells, respectively, due to the improved local contacts. [ABSTRACT FROM AUTHOR]

Self‐generation power devices based on the radiative cooling effect have intense potential applications in the energy conversion field. A selective solar absorber is introduced into thermoelectric generator (TEG) devices based on radiative cooling emitters (RCEs). The self‐generation device can work continuously for 24 h, and the output power is greatly enhanced. The RCE is prepared as a polydimethylsiloxane–Al structure by a simple squeegee method. The solar selective absorber (SSA) of the W–Si–O laminated film is prepared by the magnetron sputtering method. Its working temperature can reach as high as 85 °C under AM1.5 sunlight. The calculation results prove that the selective solar absorber can achieve 1.55 times the net heating power of an ideal blackbody at the same working temperature of 85 °C. The assembled self‐generation power device achieves output powers of 695.1 and 5.23 mW m−2 on clear days and nights, respectively, as well as an output power of 7.64 mW m−2 even in the cloudy daytime. The result of theoretical calculation proves that the addition of SSA can greatly increase the temperature difference and the average working temperature, which improves the efficiency of the TEG and the output power of the device. [ABSTRACT FROM AUTHOR]

An industrially proven method for increasing cell efficiency of monocrystalline P‐type PERC cells is reported, whereby a layer of silicon oxide or silicon oxynitride (SiOx/SiOxNy) is sandwiched between aluminum oxide (AlOx) and silicon nitride (SiNx) in the rear passivation stack, forming an AlOx + SiOx/SiOxNy + SiNx structure. This additional layer will theoretically improve the rear side optical and electrical properties for the cell. By adjusting the flow ratio of N2O:NH3, SiOx/SiOxNy with different refractive indices were fabricated. Optimization of the SiOx film thickness showed a 0.11% efficiency gain in monofacial P‐type PERC cells because of higher short‐circuit current (Isc) and fill factor (FF), whereas optimization of the SiOxNy film refractive index showed a 0.05% efficiency gain in bifacial P‐type PERC cells due to the improvement of Isc and FF too. The current gain is believed to be benefited from the optimized light‐absorbing performance of the composite passivation layer structure. Furthermore, it is demonstrated that the refractive index of the SiNx capping layer had to be tuned after the incorporation of SiOx/SiOxNy to improve the cell efficiency. [ABSTRACT FROM AUTHOR]

A stress‐induced failure study on a high‐temperature air‐stable ceramic composite solar selective absorber (SSA) based on a W–SiO2 system is reported. The as‐prepared SSA exhibits excellent spectral and structural stability after annealing in air at 500 °C for 36 h, proving its thermal stability against air corrosion. However, once the temperature is elevated to 600 °C, optical performance degradation and coating cracking happens. The X‐ray diffraction (XRD) patterns reveal that an O‐induced phase transition process from α‐W to β‐W occurs at the interface between the W IR reflector and W–SiO2 layer during deposition. The phase transition induces immense internal stress, which becomes the incentive of crack generation. Further increasing the annealing temperature, drastic structural changes of oxidized W become the driving force for crack propagation and hole expansion, leading to a failure analogous to a volcanic eruption. To improve the temperature limit of coating, a Ni–SiO2 stress buffer layer is introduced and successfully reduces the internal stress through Ni atom substitution for W atoms. Therefore, the optimized SSA keeps stable at 600 °C and the cracking temperature increases to 650 °C. These results suggest that the W–SiO2‐based SSA is a good candidate for air‐stable high‐temperature solar thermal conversion. [ABSTRACT FROM AUTHOR]

Metal-assisted chemical etching (MACE) method is an efficient way to improve the power conversion efficiency of solar cell by developing nanostructures. Normally, hydrogen peroxide is widely used as an oxidizing agent, through which anisotropic etching of nanostructures could be achieved. Here, nanoscale textured multi-crystalline silicon (mc-Si) solar cell with an efficiency of 18.13% was fabricated by MACE method with potassium permanganate (KMnO4) as an oxidizing agent. The isotropic etching by KMnO4 showed the great uniformity of surface reflectance, corresponding to the isotropic oval pits. The solar cell presented an increase of 0.72mA · cm−2 in the short-circuit current density comparing with the mc-Si solar cell fabricated by the traditional process. Though the efficiency still needed optimizing, isotropic etching for mc-Si would lead a new tendency for MACE technique. [ABSTRACT FROM AUTHOR]

Metal-assisted chemical etching (MACE) method is an efficient way to improve the power conversion efficiency of solar cell by developing nanostructures. Normally, hydrogen peroxide is widely used as an oxidizing agent, through which anisotropic etching of nanostructures could be achieved. Here, nanoscale textured multi-crystalline silicon (mc-Si) solar cell with an efficiency of 18.13% was fabricated by MACE method with potassium permanganate (KMnO4) as an oxidizing agent. The isotropic etching by KMnO4 showed the great uniformity of surface reflectance, corresponding to the isotropic oval pits. The solar cell presented an increase of 0.72mA · cm−2 in the short-circuit current density comparing with the mc-Si solar cell fabricated by the traditional process. Though the efficiency still needed optimizing, isotropic etching for mc-Si would lead a new tendency for MACE technique. [ABSTRACT FROM AUTHOR]

Acid texture is difficult for diamond wire sawn (DWS) multicrystalline silicon (mc-Si) wafer owing to the inhomogeneous distribution of damage layer on the surface. In this article, metal-assisted chemical etching (MACE) has been selected for introducing a porous seeding layer to induce acid texturing etching. SEM results show that the oval pit structures coverage get obvious improvement even on the smooth areas. Owing to the further improved light absorption ability by second MACE and nanostructure rebuilding (NSR) process, nanostructured DWS mc-Si solar cell has exhibited a conversion efficiency of 17.96%, which is 0.45% higher than that of DWS wafer with simple acid texture process. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Microcrystalline silicon thin films were deposited on glass and stainless steel (SS) substrates by hot-wire chemical vapor deposition with negative substrate bias varying from 0 to −600 V. The structural properties of these films were characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectra, and scanning electron microscopy. The results show that the crystallinity and compactness of the films deposited on glass first improved by increasing the substrate bias from 0 to −300 V, and then deteriorated by further elevating the substrate bias from −300 to −600 V. However, the crystallinity of films deposited on SS with negative substrate bias deteriorated on increasing the applied substrate bias. Moreover, temperature-dependent conductivity measurements were performed to investigate the electrical properties of the boron-doped films on glass. The conductivity activation energy of the boron-doped films deposited on glass first decreased from 0.049 to 0.039 eV by varying the substrate bias from 0 to −300 V, and then increased to 0.05 eV on increasing the substrate bias to −600 V. [ABSTRACT FROM AUTHOR]

A simple but efficient strategy to synthesize millimeter-sized graphene single crystal grains by regulating the supply of reactants in the chemical vapor deposition (CVD) process is demonstrated. Polystyrene is used as a carbon source. Pulse heating on the carbon source is utilized to minimize the nucleation density of graphene on copper foil, while a gradual increase in the temperature of the carbon source and the flow rate of hydrogen is adapted to drive the continuous growth of the graphene grains. As a result, the nucleation density of graphene grain can be controlled to as low as ≈100 nuclei/cm2, and a single crystal grain can grow up to dimensions of ≈1.2 mm. Raman spectroscopy, transmission electron microscopy (TEM), and electrical-transport measurements show that the graphene grains obtained are of high quality. The strategy presented provides very good controllability and enables the possibility of large graphene single crystals, which is of vital importance for practical applications. [ABSTRACT FROM AUTHOR]

H2O2 is predominantly used as an oxidizer in traditional metal assisted chemical etching (MACE), showing a high consumption rate due to its instability at room temperature. In this work, low concentration HNO3 instead of H2O2 is investigated in Ag‐assisted chemical etching process for multicrystalline silicon (mc‐Si) wafer. In comparative experiments, black silicon wafers with a surface reflection of 6.46% are obtained using HNO3 with only 5% molar concentration quantity of H2O2. After a post nanostructure rebuilding treatment, nano‐scale inverted pyramid‐like structures are obtained. SEM images reveal that increase in HNO3 concentration lead to an increase in surface roughness with enlarged structure size. Furthermore, a linear increase in etching rate is observed when AgNO3 concentration raised from 0 to 0.8 × 10−3m. The activation energy of 95.4 eV for the HNO3/HF‐Si reaction catalyzed by Ag is obtained by Arrhenius equation. The outcomes demonstrate HNO3 as a potential alternative to conventional oxidizer H2O2 in traditional MACE process. In this article, the feasibility of replacing traditional H2O2 by low concentration HNO3 in MACE process is proved. B‐Si surface with a reflectance of 6.462% is fabricated. The increase of C(HNO3) or C(AgNO3) both leads to the raise of inverted pyramid structure size. The activation energy of Ag assisted etching reaction, 95.4 eV, is obtained using Arrhenius equation. [ABSTRACT FROM AUTHOR]