Composite materials for photovoltaics:: A realistic aim?

Layer-type microcrystalline powders of WS2, MoS2, WSe2 and MoSe2, which were tested for photoeffects with contact free microwave conductivity measurements, were incorporated into a nanostructured TiO2 matrix in an attempt to obtain macroscopic photocurrents. Even though only 10% of the microcrystals were found to be active in contact with an iodide/iodine solution, photocurrents of the order of 100 mu A/cm(2) to 1 mA/cm(2) were measured. The photoelectrochemical behavior of microcrystals was studied with space resolved photocurrent and photovoltage measurement techniques and it was attempted to understand the mechanism of current generation via the TiO2/microcrystal/electrolyte interaction. Critical and still unresolved problems are recognized to be the control and optimization of photoeffects in microcrystals and the adjustment of doping levels of the two material faces. Only small photopotentials could be observed up to now, probably due to an insufficient and inhomogeneous doping of microcrystals. More research will be needed to determine whether this strategy could lead to realistic photovoltaic systems. (C) 1999 Elsevier Science B.V. All rights reserved.