Liquid‐Tin‐Assisted Molten Salt Electrodeposition of Photoresponsive n‐Type Silicon Films

Abstract

Production of silicon film directly by electrodeposition from molten salt would have utility in the manufacturing of photovoltaic and optoelectronic devices owing to the simplicity of the process and the attendant low capital and operating costs. Here, dense and uniform polycrystalline silicon films (thickness up to 60 µm) are electrodeposited on graphite sheet substrates at 650 °C from molten KCl-KF-1 mol% K 2 SiF 6 salt containing 0.020-0.035 wt% tin. The growth of such high-quality tin-doped silicon films is attributable to the mediation effect of tin in the molten salt electrolyte. A four-step mechanism is proposed for the generation of the films: nucleation, island formation, island aggregation, and film formation. The electrodeposited tindoped silicon film exhibits n-type semiconductor behavior. In liquid junction photoelectrochemi cal measurement, this material generates a photocurrent about 38-44% that of a commercial n-type Si wafer.

Template‐Free Electrochemical Formation of Silicon Nanotubes from Silica

“…[43] Constant-voltage electrolysis is conducted, with the cell voltage between the solid cathodes and graphite anode being at 2.2-2.6 V to avoid the formation of Ca-based alloys. [31][32][33][34][35][36][37][38][39][40][41] The cathode potential (versus Ag/AgCl) was monitored in one case during constant-voltage electrolysis at a cell voltage of 2.2 V ( Figure S1, Supporting Information), which shows that the cathode potential (versus Ag/AgCl) during the two-electrode-electrolysis process is consistent with that in the CV curves in Figure 2a, further verifying the preferential reduction of AgCl and formation of Ag-Si.…”

“…[31][32][33][34][35][36][37][38][39][40][41] However, the solid-solid conversion from SiO 2 to Si makes the nucleation-growth process of Si hardly tunable, therefore construction of hollow Si nanostructure by molten salt electrolysis of silica is an insurmountable challenge. [31][32][33][34][35][36][37][38][39][40][41] As for coating a conductive buffer layer on the surface of Si nanostructures, carbon is commonly used as the candidate. [12][13][14][15][16] However, the unpleasant SiC is readily generated during molten salt electrolysis, therefore making the in situ coating strategy far from expectations.…”

“…The electrode kinetics for molten salt electrolysis of solid silica for Si extraction is governed by ohmic polarization and mass transfer of/through the solid cathode. [31][32][33][34][35][36][37][38][39][40][41] Electrolysis of SiO 2 -AgCl for Si formation ranks among the highest performance in terms of current efficiency (74%, Figure 4m) and energy consumption (12.1 kW h kg Si −1 , Figure 4m). This energyconsumption value is even lower than that of industrial production of metallurgical-grade silicon (>20 kW h kg Si −1 ), [41] promising future industrial production of Si nanotubes.…”

“…Of note, molten salt electrolysis, which is widely adopted for production of metals in industry, has been verified to be adaptable for large-scale production of silicon nanomaterials. [31][32][33][34][35][36][37][38][39][40][41] Compared with the conventional CVD method which uses toxic SiH 4 /SiCl 4 as raw materials and suffers from low production yield, [12,[17][18][19][20][21][22][23][24][25][26][27][28] the molten salt electrolysis strategy with a high production yield herein uses affordable SiO 2 as the starting material and shows a promise for practical production of Si nanotubes.…”

Electrodeposition of crystalline silicon films from silicon dioxide for low-cost photovoltaic applications

“…10–12). The film thickness can be controlled in a range of about 5 µm to more than 60 µm, on various substrates, including graphite, silicon wafers and others 27–30 . The X-ray diffraction patterns, as shown in Fig.…”