Voltammetric Study of Selenium and Two-Stage Electrodeposition of Photoelectrochemically Active Zinc Selenide Semiconductor Films in Ionic Liquid Zinc Chloride-1-Ethyl-3-Methylimidazolium Chloride

Abstract

Ionic liquid zinc chloride-1-ethyl-3-methylimidazolium chloride (IL ZnCl 2 -EMICl) with a ZnCl 2 /EMICl ratio of 40/60 mol% was used as the electrolyte to study the voltammetric behavior of Se(IV) introduced into the IL as selenium chloride (SeCl 4 ) or selenium oxide (SeO 2 ). The electrodeposition of ZnSe was performed using constant-potential electrolysis at tungsten electrodes via a two-stage approach from the IL with and without SeO 2 . The nucleation mechanism of Se at the tungsten electrodes agrees better with the three-dimensional instantaneous nucleation than the progressive nucleation based on Sharifker's model. Crystalline Se and approximately stoichiometric crystalline ZnSe electrodeposits could be obtained from this system. The ZnSe films showed photoelectrochemical activity with a bandgap energy of ∼2.5 eV. According to the experiments of the dependence of the photocurrent on the applied potential, the ZnSe film was determined to be a p-type semiconductor with the flatband potential V FB of −0. Zinc selenide (ZnSe) is a II-VI semiconductor that belongs to the chalcogenide family. ZnSe is usually obtained as a n-type semiconductor with a wide bandgap (2.67-2.7 eV). p-type ZnSe, which is very likely due to excess Se in the deposits, has been prepared using electrodeposition.1 ZnSe has been reported to be a useful material for various optoelectronic devices, such as lightemitting devices, window layers for solar cells, photovoltaic cells, laser screens, film transistors, photoelectrochemical cells, and optical components for infrared lasers. 19,25 Compared with these approaches, electrodeposition is more attractive [26][27][28][29] in terms of convenience, cost, and suitability for the large-scale production of thin films. Moreover, the surface morphology, composition, and properties of semiconductors can be flexibly controlled by adjusting the operating parameters such as electrodeposition potential or current, potential waveforms (constant potential or pulse potential), concentration of precursors, temperature, and additives. Therefore, ZnSe has been widely prepared using electrodeposition, with mostly successful results. Most electrodepositions of ZnSe were carried out cathodically in acidic aqueous baths containing Zn(II) and SeO 2 . [30][31][32][33][34][35][36][37] In acidic solutions, SeO 2 dissolves to form H 2 SeO 3 . ZnSe has also been electrodeposited from alkaline aqueous baths. [38][39][40] In alkaline solutions, Zn(II) and SeSO 3 2− are most frequently used as the precursors, and complexing agents, such as EDTA, are usually needed for forming strong complex ions with Zn 2+ to prevent the chemical precipitation of ZnSe, which is produced from the reaction between Zn(II) and SeSO 3 2− . Few studies have electrodeposited ZnSe from nonaqueous baths such as dimethylsulfoxide [41][42][43] and molten salts (CaCl 2 -NaCl at 550• C). 44,45 In almost all recent studies and applications of ZnSe semiconductors, ZnSe has been prepared using electrodeposition from aqueous baths. [46][47][48] 28,29,[50]...

Electrodeposition of Selenium in a Hydrophobic Room-Temperature Ionic Liquid

“…On the other hand, it was difficult to identify the reaction for the cathodic current peak C2 at about −1.6 V, which may be related to reduction of some oxychloro species of Se because of the high reactivity of SeCl 4 with moisture. 8 The similar cathodic current peak was also observed in 1-ethyl-3-methylimidazolium trifluoromethylsulfonate containing SeCl 4 .…”

“…8 Recently, selenium electrodeposition has been studied in 1-butyl-1-methylpyrrolidinium and 1-ethyl-3-methylimdazolium trifluoromethylsulfonate containing H 2 SeO 3 with H 2 O as a co-solvent (5 vol%) in open air conditions at various temperatures. 25,26 In situ UV-vis spectroelectrochemistry of diethyl selenite in 1-propyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)amide revealed deposition of amorphous selenium consisting of Se 8 rings and polymeric Se chains.…”

“…Especially, Se is an essential constituent of the materials for photovoltaic cells 5,6 because of photovoltaic and photoconductive properties of Se. Furthermore, such compound semiconductors containing selenium, as CdSe, ZnSe or CuInSe 2 (CIS), [7][8][9] have also been studied widely for various optoelectric applications. Various approaches including photodeposition, 10 chemical bath deposition, 11 and chemical vapor deposition 12,13 have been developed for preparation of selenium thin film.…”

“…5 Electrodeposition of the polycrystalline Se film was successfully performed in 1ethyl-3-methylimidazolium chloride-tetrafluoroborate at 30 • C. 23 The electrochemical behavior, morphology and structure of Se deposits have been reported to be influenced by Se(IV) species in 1-ethyl-3-methylimdazolium tetrafluoroborate/chloride 24 and zinc chlorid-1ethyl-3-methylimdazolium chloride ionic liquid. 8 Recently, selenium electrodeposition has been studied in 1-butyl-1-methylpyrrolidinium and 1-ethyl-3-methylimdazolium trifluoromethylsulfonate containing H 2 SeO 3 with H 2 O as a co-solvent (5 vol%) in open air conditions at various temperatures. 25,26 In situ UV-vis spectroelectrochemistry of diethyl selenite in 1-propyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)amide revealed deposition of amorphous selenium consisting of Se 8 rings and polymeric Se chains.…”

Effects of Illumination on the Electrochemical Behavior of Selenium Electrodeposition on ITO Substrates

“…As a p-type semiconductor with bandgap of 1.9 eV at room temperature, 1 the trigonal selenium thin film have received considerable attentions due to the excellent opto-electrical properties. [2][3][4] In addition, the selenium-based semiconductor compounds, including Sb 2 Se 3 , 5 CuInSe 2 6 and ZnSe, 7 have also been widely applied in solar cell owning to their direct optical transition and high absorption coefficient. Many fabrication techniques have been developed to obtain these semiconductor thin films such as vacuum deposition, 8 chemical bath deposition, 9 chemical vapor deposition 10 and electrodeposition.…”