Layer‐Type Transition Metal Dichalcogenides — a New Class of Electrodes for Electrochemical Solar Cells

The problem of the rapid anodical photoelectrochemical desintegration of visible‐light‐sensitive semiconductor electrodes (e.g. CdS, GaAs) in presently investigated continuously operating electrochemical solar cells is tackled by two improvements: a) The use of covalent layer‐type transition metal dichalcogenides as electrode material, in which photon absorption involves d‐d transitions and does not produce a splitting of chemical bonds and b) the operation of the transition metal dichalcogenides as photo‐cathodes, which is possible with p‐conducting material. The first photocell of this kind is constructed with p‐conducting natural MoS2 layer crystals and Fe2+/3+ as redox‐couple. It proved to be stable during longtime experiments. A power output of up to 1% was obtained. The limiting factor was found to be the insufficient solid state behaviour of the available natural crystals (high recombination losses through traps, weak p‐character). A considerable improvement is to be expected from better quality p‐type electrode‐material. Some development possibilities for solar cells, based on covalent semiconducting layer‐type transition metal dichalcogenides are outlined.