PREPARATION OF A LANGMUIR-BLODGETT LAYER OF ULTRAFINE PLATINUM PARTICLES AND ITS APPLICATION TO N-SI FOR EFFICIENT PHOTOELECTROCHEMICAL SOLAR-CELLS

A Langmuir layer of ultrafine platinum particles (2-6 nm in diam) has been developed on a water surface by dropping a Pt colloid solution, p repared by refluxing an ethanol-water (1:1) solution of hexachloroplat inic(IV) acid in the presence of poly(N-vinyl-2-pyrrolidone) as a stab ilizer. The layer is transferred onto a single-crystal n-type silicon (n-Si) wafer by the horizontal lifting method. The Pt particles are ra ther homogeneously scattered on n-Si, and the particle density can be controlled on a nanometer scale by changing the area of the Langmuir l ayer at the time of transfer. The open-circuit photovoltage (V(oc)) fo r photoelectrochemical (PEC) solar cells with such n-Si electrodes is inversely related to Pt-particle density, and reaches 0.635 V, much hi gher than that for n-Si coated with a continuous Pt layer (ca. 0.30 V) or that for the conventional p-n junction Si solid solar cell of a si milar simple cell structure (ca. 0.59 V). This result is in harmony wi th our previously proposed theory, the above increase in V(oc) being e xplained by the decrease in the majority carrier dark saturation curre nt density.