ABSTRACT A novel and very simple chloroplastmimic photovoltaic scheme, in which water is photolyzed by a new photocatalyst fabricated by depositing a thin film of TiO 2 on an array of carbon nanotubes (CNT), has been made. Multiple reflections within the photocatalyst extend the optical response from the ultraviolet range to the full visible range. Hydrogen ions with various concentrations are separated by an artificial thylakoid membrane, resulting in a transmembrane chemiosmotic potential, generating ion-diffusion-induced electricity. Experimental results demonstrate that the proposed simple chloroplastmimic photovoltaics can produce a photocurrent directly from visible light. 1 INTRODUCTION Chloroplasts are regarded as the most effective energy conversion plants of sunlight. Chloroplasts seize the energy of sunlight to produce the free energy stored in adenosine 5'-triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADP) via photosynthesis. Photosynthesis is an important biochemical process in which plants transform light energy from the sun into chemical energy. During photosynthesis, the ATP is synthesized by an ATP synthase enzyme by using the chemiosmotic potential across the thylakoid membranes of the chloroplasts. The hydrogen ions that are formed by the products of the photolysis of water by chlorophyll contribute to the transmembrane chemiosmotic potential. The rate at which solar radiation reaches the earth's surface is 1,020 W/m². For centuries, human beings have attempted to mimic the conversion mechanisms of chloroplasts by harnessing the energy of sunlight. The conversion mechanism of the chloroplast represents a promising new energy resource. Conventional solar cells exploit the photovoltaic effect of semiconductors to produce electricity directly from sunlight. Despite the great major progress made over the last decade, the use of silicon-based solar cells remains more expensive than traditional electricity generation. One promising approach for reducing costs even further involves dye-sensitized solar cells (DSSC) [1-4] that photosensitize wide-band-gap mesoporous oxide semiconductors. Michael Graetzel et al. 1 developed DSSC in 1991. The structure of a DSSC comprises of two electrodes and an electrolyte that contains iodide. One electrode is dye-absorbed nanoporous titanium dioxide (TiO 2 ) that is deposited on a transparent electrically conducting substrate -usually made of indium tin oxide (ITO). The other is only a transparent electrically conducting substrate. When sunlight passes through ITO, any dyes adsorbed on it are photo-excited. One of the electrons in the dye jumps from the valence band to the conduction band in TiO 2 . The electron then diffuses across the porous film of TiO 2 , arriving at ITO, and through the iodidecontaining electrolyte, returning the oxidized dye molecules to their initial state. Since the DSSC uses the redox reaction of the electrolyte, it has been compared to the photosynthesis of chloroplasts. The performance of DSSC can be further improved using TiO 2 nanotube arrays, as demonstrated by recent works that water can be split using carbon-doped TiO 2 nanotube array
