Preparation of a Langmuir‐Blodgett Layer of Ultrafine Platinum Particles and Its Application to n‐Si for Efficient Photoelectrochemical Solar Cells

Abstract

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, prepared by refluxing an ethanol-water (1:1) solution of hexachloroplatinic(IV) acid in the presence of poly(N-vinyl-2-pyrrolidone) as a stabilizer. The layer is transferred onto a single-crystal n-type silicon (n-St) wafer by the horizontal lifting method. The Pt particles are rather homogeneously scattered on n-St, and the particle density can be controlled on a nanometer scale by changing the area of the Langmuir layer at the time of transfer. The open-circuit photovoltage (Voc) for photoeleetrochemieal (PEC) solar cells with such n-St electrodes is inversely related to Pt-particle density, and reaches 0.635 V, much higher than that for n-St coated with a continuous Pt layer (ca. 0.30 V) or that for the conventional p-n junction Si solid solar cell of a similar simple cell structure (ca. 0.59 V). This result is in halTnony with our previously proposed theory, the above increase in Voc being explained by the decrease in the majority carrier dark saturation current density.The main target in recent solar-cell research lies in how to fabricate low-cost solar cells without lowering conversion efficiency. Many studies have been made toward this aim, mostly using polycrystalline thin films of St, i-~ CdTe/ CdS, 6 CuInSe2, 6 or granular Si 7 for solid-state solar cells. Various types of photoelectrochemical (PEC) solar cells have been studied, using single crystal St, 8 polycrystalline FeS2, 9 dye-modified polycrystalline TiQ, 10 among others.We have been studying solar cells of a new type, for both PEC and solid-state application, in which an Si semiconductor is modified with ultrafine metal particles. I~ 18 PEC solar cells of this type, with single crystal n-St electrodes, generate extremely high open-circuit photoveltages (Voc) of 0.62-0.685 V, i~-~6 and conversion effieiencies up to 14.9%.18 Though the n-St PEC cells have inadequate stability for long-term practical application, the principle and the fabrication techniques can be applied to stable solidstate solar cells of the same type. ~I'~8 The method is also expected to be applicable to polycrystalline Si thin films.A continuing problem for the above-type solar cells is that, though the n-St PEC cells give very high Vocs mentioned above, the Voc values are scattered from electrode to electrode in the range of _+0.02 V, for ostensibly similar preparations. This is probably due to scatter in the size and the separation of the metal particles on n-St for the metalparticle deposition methods adopted thus far. Theoretically, it is of key importance for obtaining high Voc to control the size and the separation of the metal particles on Si on a nanometer scale, the ideal size and separation for n-St of 1 ~ cm being estimated to be about 5 nm and ca. 20 nm, respectively. :2 To control the metal particles on Si on such an ultrafine scale is quite difficult at present. It is impossible to attain it by use of the present photolithogr...

Structural Control of Semiconductor Surfaces on Atomic and Nanometer Scales for Efficient Solar Energy Conversion

“…Illumination of n-Si produced H2 and I2 (or I, ) at both sides of -Si. A conversion efficiency of 3.4% was obtained under simulated solar AMI.5 (100 mW/cm2) illumi- nation. The efficient conversion is achieved by the fact that the UFB of n-Si in the HI/I2 is more negative than that in the HBr (surface-band asymmetry), which produces band bending in the n-Si chip even in a photo-stationary state under illumination.…”

“…Quantitative analyses using electrodes with well-regulated distributions of Pt particles, prepared by use of Langmuir-Blodgett layers of Pt particles [3], have shown that ideal, minority-carrier controlled solar cells can be fabricated by this method [4]. We have also reported that the principle can be extended to preparation of solid-state solar cells with higher stability [5].…”

Directed self‐assembly by photostimulation of an amorphous semiconductor surface

“…The approach to directed self-assembly described here should be capable of producing single-layer particle arrays for sensors, 33 solar cells, 34 high-density/low-power storage media, 35 and other electronic devices. 36,37 The arrays can also be employed as ordered seed layers for the subsequent deposition of sintered particle films.…”

“…However, when the films become sufficiently thin, order imposed by an initial seed layer can propagate throughout the film when subsequent layers are deposited by colloidal techniques. 42,43 Certain beneficial film properties, particularly optical properties, 12,34,42 become most pronounced with specific kinds of particle ordering. Templating using a suitably chosen pattern in the seed layer offers the possibility of tailoring this ordering.…”

Silicon Nanowires with MoSxand Pt as Electrocatalysts for Hydrogen Evolution Reaction

“…Photoanodes of photoelectrochemical (PEC) cells have been extensively investigated [15][16][17][18], because Si nanowires (SiNWs) can provide several performance and manufacturing benefits [19]. Many methods have been developed for preparing SiNWs, such as chemical vapor deposition (CVD) [20], electron beam lithography (EBL) [21], pulsed laser deposition (PLD) [22], molecular beam epitaxy (MBE) [23], and wet chemical etching (WCE) [24].…”