Kirthi Tennakone

Enhanced Efficiency of a Dye-Sensitized Solar Cell Made from MgO-Coated Nanocrystalline SnO2

Nanocrystalline SnO2-based dye-sensitized photoelectrochemical solar cells have very low open-circuit voltages of 325–375 mV and efficiencies of ~ 1%. However, on coating the SnO2 crystallites with a thin film of MgO, the voltage and efficiency are increased to 650–700 mV and ~ 6.5%, respectively. Evidence is presented to show that the photoexcited dye on the outer MgO shell could tunnel electrons to SnO2 and that the low probability of reverse tunneling suppresses recombinations, thus increasing the efficiency. An explanation is also given as to understand why dye-sensitized TiO2 cells are more efficient than those made from SnO2 alone.

Efficient dye-sensitized photoelectrochemical cells made from nanocrystalline tin(IV) oxide–zinc oxide composite films

Dye-sensitized photoelectrochemical cells based on nanocrystalline films of TiO2 yield energy conversion efficiencies ~10%. The efficiencies of similar cells with films of other oxide materials (SnO2, ZnO) are well below the above value. However, the cells made from SnO2–ZnO composite films give efficiencies comparable to TiO2 cells. Two types of composite systems with SnO2 and ZnO are possible. In the first type, SnO2 crystallites are covered with an ultra-thin (<1 nm) outer shell of ZnO2 and in the second type, the film comprises SnO2 crystallites (~10 nm) with a thin ZnO outer shell and larger ZnO particles (~100 nm). The short-circuit photocurrent and efficiency of these cells are ~17 mA cm−2, 19 mA cm−2 and 7%, 8% respectively. This paper explains in detail how a thin shell of ZnO on SnO2 could effectively counteract recombinations of electrons with acceptors in the electrolyte (e.g., I3−) and increase the efficiency although SnO2 and ZnO are individually not good materials for dye-sensitized photoelectrochemical cells. In the second type, larger ZnO crystallites reduce the rate of geminate recombinations, in addition to the effect of the outer shell.

Sensitization of Nanocrystalline SnO2 Films with Indoline Dyes

Using newly synthesized indoline dyes as sensitizers for photoelectrochemical solar cells based on SnO2 nanocrystalline films, an energy conversion efficiency of 2.8% is achieved, compared with 1.2% for ruthenium bipyridyl dye (N-719) under the same experimental conditions. It is suggested that the formation of nonquenching aggregates and the better passivation of surface states on SnO2 by indoline dyes are instrumental factors in giving a higher efficiency for the cell sensitized with this dye.

Continuous flow photochemical reactor for solar decontamination of water using immobilized TiO2

A photochemical reactor is designed for solar decontamination of organic pollutants in water, where the nanocrystalline photocatalyst TiO 2 is immobilized on glass. The reactor modules could be connected in series and/or parallel to achieve desired #ow rates under di!erent conditions of illumination and degree of contamination. Methyl violet and phenol was found to completely degrade under solor irradiation and #ow rates of 102}138 ml/h. ( 1999 Elsevier Science B.V. All rights reserved.

Dye-sensitised solid-state photovoltaic cells

A thin layer of dye sandwiched between p-CuCNS deposited on a copper substrate and n-SnO2 coated transparent glass was found to yield photocurrents resulting from light absorption in the dye. The mechanism of photocurrent generation is discussed.

A wet solar cell with a p-CuxS/n-CdS junction photocathode

Polycrystalline copper sulphide (p-CuxS) shows a feeble cathodic photoresponse in electrolytic media. When a thin film of n-CdS is deposited, the cathodic photocurrent quantum efficiency is increased by several orders of magnitude. The mechanism involved is discussed.