Photoelectrochemical Behavior of n‐Si Electrodes Protected with Pt‐Polypyrrole

Highly stable photoanodes based on single crystal n‐Si protected with a thin coating of Pt and electrochemically grown polypyrrole films have been studied. A power conversion efficiency of 5.5% under illumination of 55 mW/cm 2 tungsten‐halogen light is reported with an iodide/triiodide electrolyte. The cells exhibit long‐term stability over a time period of weeks. The operating characteristics of the junctions yield high fill factors and rapid electron transfer kinetics at the interface. Values of the junction quality factor as low as 1.1 have been achieved showing almost ideal Schottky junction behavior. The open‐circuit voltage as a function of the redox potential of the electrolyte shows substantial fermi level pinning at the interface. The physical structure of the junctions has been studied with AES sputter profiling techniques. The main factor limiting the power conversion efficiency of the present devices is low short‐circuit photocurrent due to light absorption in the concentrated iodide/triiodide electrolyte.