Dye‐sensitized solar cells (DSSCs) based on organic dyes adsorbed on nanocrystalline TiO2 electrodes have received considerable attention because of their high incident solar light‐to‐electricity conversion efficiency and low cost of production. A number of organic dyes have so far been developed, and the relationship between their chemical structures and the photovoltaic performances of DSSCs based on the dyes has been examined. To create high‐performance DSSCs, it is important to develop effective organic dye sensitizers, which should be optimized for the chemical structures to possess good light‐harvesting features, to provide good electron communication between the dyes and a TiO2 electrode, and to control the molecular arrangements on the TiO2 electrode. The aim of this microreview is to highlight the design and synthesis of organic dyes for DSSCs based on recent work of organic chemists. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The authors have noticed an error in the structure of compound PS-1 in Scheme 1 of their Review. The corrected version of PS-1 is presented below. The authors apologize for this error and for any inconvenience caused.

We observed high and persistent spontaneous buildup of the surface potential ͑SP͒ upon vacuum deposition of tris͑8-hydroxyquinolinato͒ aluminum͑III͒ (Alq 3) on an Au substrate under dark conditions. SP determined by the Kelvin probe method reached 28 V at a thickness of 560 nm and the surface of the Alq 3 film was positively charged. We propose a model in which preferential orientation of the dipole moments of Alq 3 molecules is the origin of this buildup of the SP. The intensity of second-harmonic generation was also dramatically increased by the deposition of Alq 3 under dark conditions, which supports the notion of a buildup of dipole layers. This giant surface potential was almost completely removed by irradiation of Alq 3 molecules with visible light, and irradiation during deposition also prevented the buildup of SP.

Firmly attached: The short‐circuit photocurrent density and conversion yields of solar cells based on pyridine‐containing donor–acceptor π‐conjugated (D‐π‐A) dyes (see scheme) are greater than those for conventional D‐π‐A dye sensitizers that bear a carboxy group as the electron‐withdrawing anchoring group. The dyes are attached to the surface by coordinate bonding with the Lewis acid sites of TiO2.

Molecular oxygen species formed on the surface of partially reduced TiO 2 (rutile) nanoparticles have been studied by in situ electron spin resonance (ESR) and diffuse-reflectance spectroscopies. ESR signals due to O 2 -(g z ) 2.020) and Ti 3+ appeared upon visible-light illumination at 77 K and vanished by raising the temperature in the dark. The numbers of O 2 and Ti 3+ radicals formed by sub-band-gap illumination were equal, suggesting a reversible electron transfer between peroxo O 2 2species and the adjacent Ti 4+ ion at an oxygen vacancy site on the TiO 2 surface:The ESR intensity was saturated by a prolonged illumination and a surface coverage of O 2 molecules adsorbed at the oxygen vacancy site was evaluated as 1.3 × 10 13 sites cm -2 . The spectral response for the generation rate of O 2 exhibited a broad peak at around 480 nm, in agreement with the absorption band observed by the diffuse-reflectance measurements. It was concluded that F-type color centers generated in subsurface layers of TiO 2 absorb the visible light to induce indirectly the electron-transfer reaction from O 2 2to Ti 4+ at the surface oxygen vacancy site.