n-TypeSi-based photoelectrochemical cell: Newliquid junction photocell using anonaqueous ferricenium/ferr ocene electrolyte

n-Type Sihasbeenshown toserve asastable photoanode inacell for theconversion oflight toelectricity. The other components ofthecell areaPtcathode andanelectrolyte consisting ofanethanol solution of(n-Bu4N)C104 with aredox couple offerricenium/ferrocene. Datafrom atwo-compartment celshowthat ferrocene isoxidized toferricenium with100i 2%current efficiency attheSiphotoanode. Furthermore, pro- longed irradiation oftheSiinaone-compartment cell yields constant photocurrent andoutput characteristics. Themaximum open-circuit photopotential is-700mV,andtheshort-circuit quantum yield forelectron flow atlowlight intensity exceeds 0.5. Conversion ofmonochromatic 632.8-nm light toelectricity with-2%powerefficiency atanoutput voltage of-200mV hasbeensustained. These results represent astable n-type Si- based photoelectrochemical cell. Conversion oflight toelectricity with devices called photo- electrochemical cells hasbeen anarea ofconsiderable activity inthelast 2years (1-16). Except for onecell that uses ap-type CdTephotocathode (12), thekeyelement ofsuch cells isan n-type semiconducting photoanode. Therecent developments with nonoxide, n-type semiconductor-based cells have hinged ontheability tofind mechanisms forcompletely eliminating deleterious photoanodic decomposition reactions ofthesemi- conductor itself. All n-type materials examined sofar seemtobeenergetically capable ofundergoing photoanodic dissolution (ref. 17;A.J. Bard andM.S.Wrighton, unpublished data), andtherefore any photoinduced interfacial electron transfer processes will bein