Shaoyuan Li

An Innovative Metal Ions Sensitive “Test Paper” Based on Virgin Nanoporous Silicon Wafer: Highly Selective to Copper(II)

Developing an innovative “Test Paper” based on virgin nanoporous silicon (NPSi) which shows intense visible emission and excellent fluorescence stability. The visual fluorescence quenching “Test Paper” was highly selective and sensitive recognizing Cu2+ at μmol/L level. Within the concentration range of 5 × 10−7 ~50 × 10−7mol/L, the linear regression equation of IPL = 1226.3-13.6[CCu2+] (R = 0.99) was established for Cu2+ quantitative detection. And finally, Cu2+ fluorescence quenching mechanism of NPSi prober was proposed by studying the surface chemistry change of NPSi and metal ions immersed-NPSi using XPS characterization. The results indicate that SiHx species obviously contribute to the PL emission of NPSi, and the introduce of oxidization state and the nonradiative recombination center are responsible for the PL quenching. These results demonstrate how virgin NPSi wafer can serve as Cu2+ sensor. This work is of great significant to promote the development of simple instruments that could realize rapid, visible and real-time detection of various toxic metal ions.

Research on surface nano-texturation and wet-chemical passivation of multi-crystalline silicon wafer

Surfaces nano-texturing has triggered off much attention for trapping sunlight to improve the efficiency of solar cells. Silicon nanowire (SiNWs) arrays, with excellent antireflection performance, will hopefully improve photoelectric conversion of solar cells, however, the deteriorated effective carrier lifetime seriously limits efficiency enhancement of solar devices. Until now, the effect of SiNWs structure on effective carrier lifetime remains unexplored. Herein, the effects of fabrication parameters on the morphology structure and effective carrier lifetime of textured mc-Si were studied in detail. We also firstly discover that the relationship of SiNWs arrays length and effective carrier lifetime shows the negative exponential relation. Moreover, the effects of ethanolic iodine (I–E) concentration, immersion time, and surface pre-conditioning (with and without native oxide) on surface passivation of SiNWs arrays were investigated. It is found that more effective surface passivation could be achieved for the SiNWs arrays with shorter length. Meanwhile, the HF dipping pretreatment is conducive for SiNWs passivation, and which is attributed to Si–Hx termination with lower dissociation energy.

Effect of Rapid Heat Treatment on the Crystal Defect Evolution and Electrical Properties of Highly Efficient Polycrystalline Silicon

The existence of a large number of crystal defects in polycrystalline Si(poly-Si) has a significant impact on its electrical property. In order to solve this problem, this study adopts the industrially produced native efficient poly-Si wafers, with 120 s rapid heat treatment experimental conditions under different temperatures. The evolution of the poly-Si crystal defects such as the grain boundary and dislocation as well as the changes in the electrical properties of the samples before and after annealing have been analyzed.. The results show that the annealing process causes a significant reduction in the defects in the samples significantly and improvement in the electrical performance. After annealing at 1200 ∘C, the dislocation density of ploy-Si decreases to 710 cm−2 from 1120 cm−2, revealing a drop of 36.61%. Furthermore, a 1.62% reduction in the high Σ value (Σ27) grain boundary and 3.19% increase in the Σ3 grain boundaries. After the heat treatment, the minority carrier lifetime of the sample increases by up to 0.6 μs. In addition, the size of the grains increases and the dislocation density reduces while the grain orientation is not changed during the heat treatment. The results show that the performance of poly-Si does not linearly improve with temperature, but is related to the crystal structure of Si.

Boron Removal from Silicon Using Secondary Refining Techniques by Metallurgical Method

Impurity removal, the purification process from metallurgical grade silicon (MG-Si) required to obtain solar grade silicon (SoG-Si), is crucial to the preparation of silicon-based solar cells. Some processes for boron removal by metallurgical method were reviewed. Secondary refining techniques, including gas blowing, slag treatment, plasma refining, solvent refining and other refining silicon techniques were summarized. The effects of gas species and slag systems on boron removal efficiency were emphatically discussed. Experimental and theoretical investigations show that a united technique of combining water vapor and oxygen gases blowing with slag treatment containing chloride or fluoride has achieved an amazing improvement for boron removal from molten silicon. Plasma refining and solvent refining also display high efficiency but acid leaching treatments, vacuum volatilization, electron beam and directional solidifications are hardly effective to boron removal. As for the potential industrial application of this united technique, the authors propose that some experimental and theoretical studies in dynamics should be further explored.

Research on controllable preparation and antireflection properties of zigzag SiNWs arrays

ABSTRACT In this work, an alternative metal-assisted chemical etching method is proposed to fabricate large-area uniform zigzag silicon nanowires. The effects of deposition time, etching time, HF concentration and H2O2 concentration on the nanostructure of nanowires were systematically investigated. The results demonstrate the suitable preparation concentrations in the alternating etching process are HF([SI]/[SII] = 9.2 M/2.3 M) and H2O2{[SI]/[SII] = (0.04 M∼0.26 M)/(0.4 M∼0.65 M)}. Moreover, the anti-reflec-tion properties of the resulting zigzag SiNWs arrays have been studied, the average reflectance is almost lower than 10% at wavelength range of 200∼1200 nm. The superior anti-reflection performance of zigzag SiNWs shows a huge potential application in high-efficiency silicon solar cells.

Influence of fabrication parameters on the nanostructure of Si-NWs under HF/Fe(NO3)3 etching system

Abstract Large-area and oriented silicon nanowire arrays have been successfully fabricated through a two-step metal-assisted chemical etching process at room temperature. The effects of key fabrication parameters (AgNO3 concentration, Fe(NO3)3 concentration, and etching time) on the silicon nanowire nanostructure were carefully investigated. The Raman spectra of silicon nanowires prepared under different etching times have been recorded and analyzed. The porosity and length of the nanowire increases with the increase in AgNO3 concentration from 0.002 mol L−1 to 0.1 mol L−1, which indicates that the re-dissolved Ag+ ions would work as the main oxidative species and catalyze the vertical and lateral etching of nanowires, leading to silicon nanowire growth and porous structure formation.