Electrochemical synthesis of CdSe/CdTe nanowires for hybrid photovoltaic structures
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Electrochemical synthesis of CdSe/CdTe nanowires for hybrid photovoltaic structures Jelena Gurevits, Sergei Bereznev, Valdek Mikli, Revathi Naidu, Enn Mellikov, Julia Kois Tallinn University of Technology, Department of Materials Science, Ehitajate tee 5, 19086 Tallinn, Estonia ABSTRACT Advanced electrochemical technique was elaborated to fabricate self-organized CdSe nanowire structures from aqueous electrolytes on ITO coated glass substrates. We have recently been demonstrated successful electrochemical formation of free-assistent CdSe nanowire structures with diameter around 30 nm. This work has extended our previous research of electrodeposition of Cd chalcogenide (CdSe, CdS) nanowires to formation of core-shell CdSe/CdTe photosensitive nanowire structures. CdSe nanowire structures were synthesized potentiostatically from an acidic solution of H2SeO3 and CdCl2 at room temperature. Then the CdSe (core) nanowires were further passivated with CdTe (shell) thin film by method of electrochemical deposition from acidic solution of H2TeO3 and CdCl2. The effect of interfacial passivation with CdTe layer on the performance of the prepared photovoltaic structures was investigated and special account was paid to the morphology, composition and photovoltaic properties of obtained CdSe/CdTe nano-layers. It should be noted, that electrically conductive polymer photoabsorbers (poly (3-octylthiophene) etc.) were applied successfully for preparation of high work-function ohmic contact-sensitizer layer to CdTe shells. The electrodeposition and spin-casting techniques were applied step-by-step to prepare complete hybrid photovoltaic structures. INTRODUCTION In recent years, studies of hybrid nanostructures have attracted a great interest in the field of solar cell application, [1]. Various nanosized semiconductors have been studied, based on CdS [2], CdSe [3], CdTe [4] and Sb2S3 [5], in the fabrication of optoelectronic devices. Among these materials, CdSe and CdTe are promising candidates for hybrid solar cell structures, due to its optical energy band gap of about 1.70 eV and 1.45 eV respectively, which have a strong absorption in solar spectrum. Different aqueous and nonaqueous methods have been applied for the synthesis of CdSe nanostructures e.g. chemical bath deposition, dip-coating, ionic layer adsorption, molecular beam epitaxy and chemical vapour deposition [6, 7]. As an alternative, electrodeposition is a commercially important process because of its simplicity, low cost as well as possibility for large-scale production. A method for electrochemical deposition of various self organized CdSe structures (nanofibers, nonotubes and pearl-chain structures) was developed in our laboratory [8]. In this work we used electrodeposited CdSe nanowire core and CdTe shell with a covered conductive polymer layer to fabricate hybrid PV structures.
EXPERIMENTAL DETAILS Hybrid PV glass/ITO/CdSe/CdTe/polymer composite nanowire structures were fabricated in three main steps: (i) electrochemical deposition of CdSe nanowires on glass/ITO su
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