K. Tennakone

Dye-sensitized solar cell with the hole collector p-CuSCN deposited from a solution in n-propyl sulphide

Abstract A method is devised for the deposition of CuSCN on ruthenium bipyridyl dye coated nanocrystalline TiO2 films from a solution in n-propyl sulphide. The dye-sensitized solid state photovoltaic cell formed was found to yield higher short-circuit photocurrent, open-circuit voltage and efficiency compared to the cells made with CuSCN by other deposition techniques. Factors affecting the stability of the cell are investigated.

A solid-state photovoltaic cell sensitized with a ruthenium bipyridyl complex

Ruthenium bipyridyl complexes have been used as efficient sensitizers for photoelectrochemical cells based on nano-porous films of . It is found that cis-dithiocyanate-bis(2,2-bipyridyl-4,4-dicarboxylate) ruthenium (II) can be used as the sensitizer in a solid-state photovoltaic cell in which a monolayer of the sensitizer is sandwiched between nano-porous n- and p-CuI. The data on performance of the cell and the problems encountered in construction of dye-sensitized solid-state photovoltaic cells are described.

Dye-sensitized solid state photovoltaic cell based on composite zinc oxide/tin (IV) oxide films

Dye-sensitized fully solid state cells having the structure of rough n-type semiconductor film comprising zinc and tin(IV) oxide/Ru-bipyridyl complex/p-CuI are found to generate high short-circuit photocurrents and open-circuit voltages in contrast to the cells of same type made with a single oxide (tin(IV) or zinc). The mechanism involved is explained as suppression recombinations of photogenerated carriers and dye ions resulting from interparticle charge transfer.

Suppression of recombinations in a dye-sensitized photoelectrochemical cell made from a film of tin IV oxide crystallites coated with a thin layer of aluminium oxide

A dye-sensitized photoelectrochemical cell consisting of a film of SnO2 crystallites coated with ultrafine particles of Al2O3 generates an exceptionally high open-circuit voltage as compared to a cell made only from SnO2. Al2O3 coating on SnO2 improves the efficiency and the fill factor while delivering reasonably high photocurrents. Photoexcited dye molecules on Al2O3 injects electrons into the conduction band of SnO2 via tunnelling through the Al2O3 barrier. Suppression of recombinations of electrons with the dye cations and the acceptors at the electrolytic interface build up the quasi-Fermi level in SnO2 with an impressive increase of the open-circuit voltage.

Nanoporous n-/selenium/p-CuCNS photovoltaic cell

On illumination, selenium deposited on nanoporous n- transfers photogenerated electrons into . When p-CuCNS is coated on top of the selenium deposited on nanoporous n-, holes are directed into the p-CuCNS. A photovoltaic cell of nanoporous n-/selenium/p-CuCNS based on the above charge transfer process generates a photocurrent of and a photovoltage of mV at simulated sunlight. The efficiency of the cell seems to be limited by surface recombination and the presence of voids in the film. Photoelectrochemical experiments also indicate that when selenium is deposited on nanoporous n- photogenerated electrons in selenium are efficiently transferred to .

Highly stable dye-sensitized solid-state solar cell with the semiconductor 4CuBr 3S(C4H9)2 as the hole collector

Construction of a dye-sensitized solid-state solar cell with the semiconductor 4CuBr 3S(C4H9)2 as the hole collector is reported. The cell is unusually stable compared to dye-sensitized solid state cells reported previously and delivers a short-circuit photocurrent and an open-circuit voltage of ∼4.3 mAu200acm−2 and 400 mV respectively, at 1.5 air mass, 1000 Wu200am−2 sunlight.

Dye-sensitized composite semiconductor nanostructures

Understanding of the charge transport and recombination mechanisms of dye-sensitized solar cells based on semiconductor nanostructures is essential for the improvement of their performance. A great deal of information on these systems have been obtained from studies on a single material (mostly TiO2 and to a lesser extent ZnO and SnO2). We have conducted extensive measurements on composite dye-sensitized nanosturctures and found that the composite systems possess unusual properties. Dye-sensitized photoelectrochemical cells made from nanocrystalline 7lms of some materials (e.g., SnO2) yield comparatively small open-circuit voltages and energy and quantum conversion e9ciencies, despite excellent dye-semiconductor interaction. However, on deposition of ultra-thin shells of insulators or high band gap semiconductors on the crystallites, a dramatic increase in the above parameters is observed. Outer shells were found to have insigni7cant or in most cases a negative e;ect on TiO2 7lms. We explain the above 7ndings on the basis of vast di;erences in the leakage rates of trapped electrons in di;erent materials which is sensitive to the e;ective electron mass. Electrons injected to the conduction band in dye-sensitization enter into shallow traps from which they get thermally reemitted to the conduction band. The building up of the electron quasi-fermi level and transport depends on this process. The spread of the hydrogenic wave function of a trapped electron increases inverse exponentially with the e;ective mass so that the electron leakage and their recombination with acceptors ‘outside’ become severe when the crystallite size is comparable to the Bohr radius of the trapped electron. Such recombinations are e;ectively suppressed by deposition of thin 7lms on the crystallites. Excited dye molecules anchored to the outer shell injects electrons to the conduction band via tunneling. ? 2002 Elsevier Science B.V. All rights reserved.

Deposition of thin conducting films of CuI on glass

Abstract A method is described for coating thin optically transparent conducting films of CuI (p-type semiconductor of band gap ∼3.1xa0eV) on glass. The dependence of the sheet resistance of the film on the level of iodine doping and other characteristics of the film are described. A minimum sheet resistance 25xa0Ω/□ (for a film of thickness ∼10xa0μm) was obtained through an optimization of iodine doping, sintering time and temperature.

Solid-state dye-sensitized photocell based on pentacene as a hole collector

Abstract A solid-state dye-sensitized photovoltaic cell consisting of vacuum deposited pentacene onto ruthenium dye-coated TiO 2 electrode doped with iodine was fabricated. Cell delivers a short-circuit current of ∼3.6xa0mAxa0cm −2 and an open-circuit voltage of ∼415xa0mV at 100xa0mWxa0cm –2 (1.5 air mass). The efficiency and the fill factors of the above cell are ∼0.8% and ∼0.5%, respectively. Studies of the photocurrent action spectra showed that the dye is mainly responsible for this photocurrent generation. Preliminary results under extended illumination suggested that “long term” stability of the cell is promising.

Dye-sensitization of magnesium-oxide-coated cadmium sulfide

Nanocrystalline films of cadmium sulfide sensitized with ruthenium N3 dye show only a feeble photoresponse either in the absorption region of the dye or the band gap excitation of cadmium sulfide. However, when an ultrathin outer shell of magnesium oxide is deposited on the cadmium sulfide crystallites in the film, the photoresponse in both the above regions of the spectrum are greatly enhanced. The result is explained as electron injection from excited dye molecules on the outer magnesium oxide shell to the conduction band of cadmium sulfide and suppression of the leakage of the relaxed electrons to the interface by the magnesium oxide barrier, where they undergo recombinations. Possible applications of this effect in dye-sensitized solar cells are discussed.