To evaluate electrical characteristics of photoelectrodes, we prepared photovoltaic photoelectrochemical solar cells (Fig. 1a) equipped with the Pt-nanoparticle modified porous multicrystalline n-Si photoelectrode. The multicrystalline n-Si electrode and Pt-plate counterelectrode were immersed in a redox electrolyte solution. Just before measuring the solar cell characteristics, the multicrystalline n-Si electrode was immersed in a 7.3 mol dm-3 hydrofluoric acid solution for two min under the elimination of dissolved oxygen by bubbling pure argon gas into the solution. This treatment is important to obtain high photovoltage caused by halogen atom termination of Si surface as mentioned below. A mixed solution of 7.6 mol dm-3 hydroiodic acid (HI) and 0.05 mol dm-3 iodine (I2) was used as a redox electrolyte solution of the photovoltaic photoelectrochemical solar cell. Photocurrent density versus potential (j-U) curves were obtained with a cyclic voltammetry tool. The potential of the n-Si wafer was measured with respect to the Pt counterelectrode. The multicrystalline n-Si was irradiated with a solar simulator (AM1.5G, 100 mW cm-2) through the quartz window and a redox electrolyte solution ca. 3 mm thick.
Fig. 9. Reflectance spectra of multicrystalline n-Si wafers: curve a after immersion in sodium hydroxide solution for saw damage layer removal; b, c, and d prepared under the conditions a, d, and g in Table 1, respectively.