The idea of dye-sensitization of inorganic materials has been around for a long time, and a vast amount of literature exists on this subject. The first studies of photoelectrochernical effects in dye-sensitized TiO2 for solar energy conversion were carried out by Deb et al. (Unpublished Report on Project SECSC (Solar Energy Convertion and Storage cell) Optel Corporation, Princeton, NJ, 1975-76), in the mid-1970s. A breakthrough occurred in recent years when Graetzel (Nature 414 (2001) 338) reported a photoelectrochemical solar cell in which a thin film based on nanoparticles of TiO2 was sensitized by a more efficient and stable dye system based on Ru(11)-complexes. Some of the key research issues that are currently being addressed at NREL include: device fabrication and characterization, role of structural properties of TiO2, electron transfer processes, novel ideas on dye-sensitization and light harvesting, and applications in optoelectronic devices. The current status and future direction of research and technology development are discussed. (c) 2004 Elsevier B.V. All rights reserved.