Nanotube–Si heterojunction solar cells are fabricated by coating a thin film of double‐walled carbon nanotubes on n‐type silicon wafers. These solar cells show power‐conversion efficiencies in the range of 5–7%. The nanotubes perform multiple functions in the cells, including charge separation, charge transport, and charge collection.

The nanoporous TiO2 films utilized in dye-sensitized solar cells (DSSCs) possess a large surface-to-volume ratio, which facilitates the adsorption of sensitizing dye and the recombination due to the high density of surface traps. In this paper, nanosized PbS was fabricated on the TiO2 films. The components of the modified TiO2 film were studied by X-ray diffraction (XRD) and electron probe microanalysis (EPMA), while the structure of the film was characterized with BET physisorption and high-resolution scanning electron microscopy (HRSEM). The results showed that the PbS particles were 2-3 nm and discrete on the surface of TiO2. Diffusion photovoltage (PV) spectroscopy was employed to study the charge separation and diffusion processes inside modified and unmodified TiO2 films. The diffusion PV signals revealed that the traps on the surface of TiO2 were extremely reduced due to the presence of PbS. The results of transient photovoltage and back I-V characteristics showed that the back reaction, that is, the recombination due to the reaction between an electron on TiO2 and the hole-transporting media, was retarded significantly.

The electrically conductive function of high-molecular weight poly(ethylene oxide) (PEO) (M(w) = 2 x 10(6) g mol(-1)) was investigated when it was used to gelate liquid electrolyte to fabricate a series of polymer gel electrolytes for dye-sensitized solar cells (DSCs). With the PEO weight ratio increasing from 2.5 to 15.0% (vs. liquid electrolyte), rheological behavior measurement showed that the viscosity of the polymer gel electrolytes increased ca 465 times. However, it was observed by steady-state voltammetry and electrochemical impedance spectra (EIS) measurements that the diffusion coefficient of I(3)(-)/I(-) decreased constantly while the conductivity of the polymer gel electrolytes increased initially and then decreased. These two inconsistent behaviours showed that the mobility of Li(+) was enhanced by PEO. EIS measurement revealed that the internal resistance of the DSCs were reduced since the enhanced mobility of Li(+) was helpful for the transport of electrons within the TiO(2) film through an ambipolar diffusion mechanism. When these polymer gel electrolytes were used to assemble DSCs, the conversion efficiency of DSCs increased continuously until it reached its maximum as the PEO weight ratio increased from 2.5 to 10.0%. By optimizing the dye adsorbing time and the thickness of the TiO(2) film, a quasi-solid DSC based on a polymer gel electrolyte with a PEO weight ratio of 10.0% showed a considerable conversion efficiency, 6.12 and 10.11% under 100 and 30 mW cm(-2) illumination, respectively. Finally, a stability test indicated that the more PEO was added into the polymer gel electrolytes, the better stability was obtained for the corresponding DSCs.

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