Effect of ZnS and CdS coating on the photovoltaic properties of CuInS2-sensitized photoelectrodes

This paper presents a facile route to prepare CuInS2 (CIS) as a light absorber for solar cells. CIS was effectively deposited inside the pores of the nanoporous anatase titanium dioxide photoelectrodes with a high coverage degree. The performance of the CIS-sensitized TiO2 photoelectrodes could be substantially enhanced through a sequential coating with a CdS shell and a ZnS layer via successive ionic layer adsorption and reaction (SILAR). Electrochemical impedance spectrum (EIS), cyclic voltammetry (CV), and photocurrent experiments were employed to study the effect of CdS and ZnS coating. The CdS shell provided high surface coverage to passivate surface states. The ZnS layer acted as a potential barrier which was similar to an insulating layer employed in the conventional metal-insulator-semiconductor solar cells, allowing the adjustment of the electric field and potential distribution in the interface between the electrodes and the electrolyte and suppressing the dark current, resulting in further increase in the photoresponse. We found that the thickness of the nanoporous TiO2 films had a dramatic impact on the optical response and efficiency of CIS-sensitized photoelectrodes, with the 5 mu m sample performing much better than the 11 mu m sample, which underlined the importance of charge (or ion) transport kinetics.