One approach to improve the stability of dye-sensitized solar cells (DSSC) is the substitution of the liquid electrolyte by a p-type semiconductor. Our goal is the fabrication of such dye-sensitized p-n solar cells at low temperature by electrodeposition. ZnO is a promising n-type material, since highly porous ZnO films with excellent electron collection characteristics can be electrodeposited at low temperature using structure-directing additives. In this study, electrochemically deposited CuSCN films were investigated towards their applicability as p-type component in our concept.
CuSCN films were deposited from solutions of Cu(ClO₄) and LiSCN in ethanol/water mixtures at 0 °C and at potentials between 0.4 V and -0.4 V vs. Ag/AgCl. The film morphology was studied by scanning electron microscopy, since the formation of small CuSCN particles is necessary to achieve efficient pore filling of dye-sensitized ZnO films. It was seen that lower deposition potentials (left figure), a higher fraction of ethanol in the solvent and the addition of surfactants added to the deposition solution decreased the particle size.
Electron transport and back reaction in the dye-sensitized CuSCN films have been studied by intensity modulated photocurrent and photovoltage spectroscopy. Low f_min values with almost no dependence on the applied potential prove that porous CuSCN films have been formed (right figure). Hole lifetimes more than one order of magnitude higher than transit times indicate efficient hole collection. A flatband potential of -0.05 V and donor density of 4.3*10^-17 cm^-3 of the CuSCN films were determined by Mott-Schottky plots derived from electrochemical impedance spectroscopy.