Indian Journal of Chemical Technology Vol. 3, March 1996, pp. 112-116 Electrosynthesis and characterisation of (ZnCd)Se films on the basis of photoelectrocheinical and impedance spectral studies Kehar Singh, A K Shukla & Md Rashid Tanveer Department of Chemistry, University of Gorakhpur, Gorakhpur 273 009, India Received 20 March 1995; accepted 20 July 1995 (ZnCd)Sefilmsof variablecompositionhavebeen prepared by electrochemicalcodeposition.The electrodepositshave been tested for their photoresponsiveness;and characterisedby photoaction spectralstudies and impedancemeasurements.These results are used for the estimationof capacit- anceandcorrosionbehaviourof thepreparations. ments were carried out using Electrochemical Measurement System (Model 378 EG & G Prin- ceton, Applied Research, USA) consisting of pot- entiostat (Model 273) and a lock-in amplifier (Model 5208) in conjuction with ffiM Personal Computer. 2.38 3.10 3.55 20.4 24.3 23.6 Film thickness, x 1O-5cm 0.00 0.01 0.02 0.03 0.04 0.05 TabJe I-Deposition conditions and film thickness values Deposition Potential = -0.70 V vs SCE Deposition time = 3h Electroplating solution 0.05 MZnS04, 0.01 M Se02 & variable concentration of CdSO 4 CdS04, Initial Steady M current, current, mA mA 0.587 0.032 0.755 0.012 1.096 0.010 1.20 0.076 1.18 0.058 1.59 0.110 Results and Discqssion Current voltage behaviour of the electro~hemi- cal system SCEITiIO.05 M znS04 +"0.01 M Se02 + 0.01 to 0.05 M CdSo41pt was used to de- termine the potential domain within which elec- trochemical codeposition is possible. Conditions under which different preparations were carried out are summarized in Table 1.·Films thickness values included in this table were estimated using procedure described elsewherelo. During deposi- tion the current initially declines somewhat rapid- ly till a time invariant value is reached. Variation of current· with time during electrosynthesis is consistent with Cottrell relationshipll. Mixed metal chalcogenides are of considerable in- terest because they are tunable in composition over a wide rangel• These materials are also im- portant from the point of view of some practical applieations2-s. In our earlier studies6•7 we de- monstrated the possibility of electrosynthesis of zinc selenide endowed with p-type semiconducti- vity. This material is of immense interest8 espe- cially if its band gap could be brought down to improve its photoresponsiveness. These studies show that band gap of zinc selenide can indeed be manipulated by inclusion of cadmium during . electrosynthesis. This mixed material exhibits en- hanced photoelectroactivity in Ii /12 redox system consistent with observed lowering of its band gap. Impedance spectral studies have also been carried out for the determination of capacitance and cor- rosion rates. Experimental Procedure For electrosynthetic work, titanium foils (1 cm x 1 em) were cleaned, polished and washed successively with acetone and distilled water, and soaked in the electroplating solution containing zinc sulphate, cadmium sulphate and selenium di- oxide having desired composition. The potential of working titanium electrode was adjusted to a predetermined optimal deposition potential9 with respect to saturated calomel electrode using a platinum counter electrode. The electrodeposits were tested for their photoelectroactivity in 0.1 M ZnS04 solution containing 0.1 M KI and 5 mMI2 using 1 kW tungsten lamp at intensity = 100 mW cm- 2. Photoaction spectral data were obtained using photoirradiator system (Model f/3.4, Ap- plied Photophysics, London) to examine the var- iation of band gap with composition of the elec- trodeposits. Electrochemical impedance measure- "'I;'lrnl"~'~1 '111I'llfll"lfflllllllll'!~I!r I I'I~I I I,jl~