Studies On The Electrodeposition, Structure And Properties Of P-type Wide-band-gap CuSCN Films

Increasing concerns on energy crisis and pollution problem arouse considerableattention on nanocrystalline photovoltaic cell (NPC) for its potentials in simpleprocess, low cost and large scale production. Developments on NPC cells and its solidhole conducting layer were reviewed. Electrodeposition and mechanisms of CuSCNas the hole conducting material as well as its filling in porous TiO2 film wereinvestigated.In this study, a stable aqueous electrolyte for CuSCN film was first prepared bychelating method;CuSCN film with high density and transmittance and goodconductivity was electrodeposited on ITO substrate;the electrodeposition mechanismwas discussed based on a Potentiostat/Galvanostat by transient current density andtransient potential method. The phase composition, crystalline morphology, opticaltransmittance, energy band gap and chemical composition of CuSCN films wereanalyzed by XRD, SEM, UV-VIS and XPS;its semiconductor characteristic wasmeasured by the differential capacity method.Instability of aqueous solution containing Cu2+ and SCN-was investigated andthe stable aqueous precursor solution for CuSCN film could be achieved with EDTAas the chelator for the first time. The solution can keep stable between RT and 80℃.CuSCN films, electrodeposited at room temperature and -0.4V from the aqueoussolution, were p-type semiconductor and composed of nanocrystals and with hightransparency (over 85%). The band-gap is about 3.7eV.Deposition mechanisms of CuSCN films at varied temperatures were studiedbased on the proposed energetic model for CuSCN semiconductor/electrolyteinterface. Cathodal current expression for p-type CuSCN electrodeposition wasdeduced. The obtained activation energy for crystal growth is 0.5eV according to theArrhenius plots of the cathodal current expression.In differential capacity method, measurement conditions had severe effect on theobtained platband potential and the acceptor concentration. The band edges of CuSCNwas pinned at the interface through using the electrolyte containing matrix ion SCN-and it did not shift with measuring frequency. Decreasing pH value can broaden thescanning potential scale and improve the measuring accuracy. Keeping the scanningspeed over 10mV/s can reduce the effect of surface state formed by ions absorption.The experimental results showed that SCN-concentration, pH value, temperatureand deposition potential had considerable influence on the redox potential of thedeposition solution, deposition efficiency, crystalline size, oriented growth, acceptorconcentration and the Fermi level.Nucleation and growth of CuSCN on porous TiO2 coating were studied. Thecurrent-voltage characteristics of TiO2/CuSCN interface showed excellentrectification, indicating that a p-n heterojunction was formed. An energy model forCuSCN filling in porous TiO2 film was proposed.