Recent Advances in Sensitized Solar Cells

Understanding the principal physical and chemical factors that govern or limit cell performance is critical for underpinning the development of next-generation sensitized solar cells. Recent studies of dye-sensitized solar cells (DSSCs) covering nanoporous (pore diameter <100 nm) one-dimensional TiO₂ nanostructured arrays and molecular voltage enhancers are discussed. Films constructed of oriented one-dimensional nanostructures, such as nanotube arrays, which are aligned perpendicularly to the charge-collecting substrate, could potentially improve the charge-collection efficiency by promoting faster transport and/or slower recombination. The extent to which transport or recombination could be affected by an oriented architecture is expected to depend on the influence of other mechanistic factors, such as the density and location of defects, crystallinity, and film uniformity. Orientational disorder within the nanotube array could also influence the transport and recombination kinetics. Such architectural disorder in titanium dioxide films is shown to have a strong influence on the transport, recombination, and light-harvesting properties of DSSCs. The mechanism by which molecular adsorbents alter the photovoltage of DSSCs is dependent on the properties of the adsorbent. In principle, an adsorbent could affect the photovoltage by either altering the recombination rate of photoelectrons in TiO₂ with oxidized redox species in the electrolyte or inducing band-edge movement. The net effect of altering the band positions and recombination kinetics can either improve or diminish cell performance. The mechanisms by which several molecular adsorbents increase the photovoltage of DSSCs are discussed.