Recently, a new class of photoelectrochemical cells based on nanoscaled porous metal oxide semiconductors (dye-sensitized solar cell) has promoted intense research due to the prospects of cheap and efficient conversion of visible light into electricity and of new applications such as transparent solar cells.[1] It is widely agreed that the electron-transfer kinetics play a major role in determining the energy conversion efficiency of dye-sensitized solar cells. [2, 3] Herein, we develop a new powerful tool to study the electron lifetime in dye solar cells as a function of the photovoltage (V oc ); the open-circuit voltage-decay (OCVD) technique. This technique has certain advantages over frequenIn summary, the temperature effect on the arrangement of stilbenoid dendrimers on HOPG is presented in this work. It is seen that SD12 molecules form well-ordered hexagonal nanostructures at 16 8C. However, if the adlayer is annealed at 65 8C, the adlayer structure is changed into a well-ordered parallelogram nanostructure in a close-packed arrangement with a higher surface coverage. The phenomenon described here supports the earlier reports on two liquid-crystalline phases for SD12.[15] The results in this research are useful in understanding the phase transition of SD12 as well as metastable complex systems with temperature. Experimental SectionSynthetic methods: SD12, SD14, and SD16 were prepared as described in the literature. [15] Sample preparation for STM observation: The molecules were dissolved in toluene (HPLC grade, Aldrich) with a concentration of less than 0.01 mg mL À1. The self-assembled adlayers were prepared by depositing a droplet of this solution onto a freshly cleaved surface of HOPG (quality ZYB, Digital Instruments). The STM images in Figure 1 a, 2 a and 3 were acquired after the solvent evaporated at 16 8C; the STM images of Figure 1 b and Figure 2 c after the substrate was kept at 65 8C for about 2 h and slowly cooled down to room temperature. The experiment was performed with a Nanoscope IIIa SPM (Digital Instruments, Santa Barbara, CA) under ambient conditions. STM tips were mechanically formed Pt/Ir wires (90/10). All STM images were recorded using the constant current mode. The specific tunneling conditions are given in the figure captions. The preliminary simulations were performed using the Hyperchem software to model the structures of the molecules.

A combination of electron lifetime measurement in nanoparticles as a function of the Fermi level position at high resolution in the potential scale with a new model to describe this dependence provides a powerful tool to study the microscopic processes and parameters governing recombination in dye-sensitized solar cells. This model predicts a behavior divided in three domains for the electron lifetime dependence on open-circuit voltage that is in excellent agreement with the experimental results: a constant lifetime at high photovoltage, related to free electrons; an exponential increase due to internal trapping and detrapping and an inverted parabolla at low photovoltage that corresponds to the density of levels of acceptor electrolyte species, including the Marcus inverted region.

Quantum‐dot‐sensitized solar cells (QDSCs) are a promising low‐cost alternative to existing photovoltaic technologies such as crystalline silicon and thin inorganic films. The absorption spectrum of quantum dots (QDs) can be tailored by controlling their size, and QDs can be produced by low‐cost methods. Nanostructures such as mesoporous films, nanorods, nanowires, nanotubes and nanosheets with high microscopic surface area, redox electrolytes and solid‐state hole conductors are borrowed from standard dye‐sensitized solar cells (DSCs) to fabricate electron conductor/QD monolayer/hole conductor junctions with high optical absorbance. Herein we focus on recent developments in the field of mono‐ and polydisperse QDSCs. Stability issues are adressed, coating methods are presented, performance is reviewed and special emphasis is given to the importance of energy‐level alignment to increase the light to electric power conversion efficiency.

The energetics of the TiO2 polymorphs (rutile, anatase, and brookite) were studied by high temperature oxide melt drop solution calorimetry. Relative to bulk rutile, bulk brookite is 0.71 ؎ 0.38 kJ͞mol (6) and bulk anatase is 2.61 ؎ 0.41 kJ͞mol higher in enthalpy. The surface enthalpies of rutile, brookite, and anatase are 2.2 ؎ 0.2 J͞m 2 , 1.0 ؎ 0.2 J͞m 2 , and 0.4 ؎ 0.1 J͞m 2 , respectively. The closely balanced energetics directly confirm the crossover in stability of nanophase polymorphs inferred by Zhang and Banfield (7). An amorphous sample with surface area of 34,600 m 2 ͞mol is 24.25 ؎ 0.88 kJ͞mol higher in enthalpy than bulk rutile.