Larissa Grinis

The importance of the TiO2/quantum dots interface in the recombination processes of quantum dot sensitized solar cells

Quantum dot sensitized solar cells (QDSSCs) present a promising technology for next generation photovoltaic cells, having exhibited a considerable leap in performance over the last few years. However, recombination processes occurring in parallel at the TiO(2)-QDs-electrolyte triple junction constitute one of the major limitations for further improvement of QDSSCs. Reaching higher conversion efficiencies necessitates gaining a better understanding of the mechanisms of charge recombination in these kinds of cells; this will essentially lead to the development of new solutions for inhibiting the described losses. In this study we have systematically examined the contribution of each interface formed at the triple junction to the recombination of the solar cell. We show that the recombination of electrons at the TiO(2)/QDs interface is as important as the recombination from TiO(2) and QDs to the electrolyte. By applying conformal MgO coating both above and below the QD surface, recombination rates were significantly reduced, and an improvement of more than 20% in cell efficiency was recorded.

Influence of the porosity on diffusion and lifetime in porous TiO2 layers

Photocurrent transients were investigated on pressed and sintered porous TiO2 layers which were immersed in electrolyte during the measurements. Unpressed porous TiO2 layers were prepared by electrophoretic deposition. The porosity of the layers was changed systematically by pressing. The surfaces of the TiO2 nanoparticles and the intimate contact between them were identically conditioned by sintering in air at 450°C after pressing. With decreasing porosity, the diffusion coefficient increased while the electron lifetime decreased. The results are discussed on the base of the change of the mean coordination number between TiO2 nanoparticles.

A two junction, four terminal photovoltaic device for enhanced light to electric power conversion using a low-cost dichroic mirror

A low-cost dichroic mirror can be used successfully for solar spectrum splitting to enhance solar to electrical energy conversion. The mirror is optimized for use with a polycrystalline silicon photovoltaic cell pc-Si. With the dichroic mirror simultaneous excitation of a medium-efficient 11.1% commercial pc-Si and a custommade high band gap GaInP cell 12.3%, yields 16.8% efficiency, with both cells operating at maximum power. Our results clearly show that what is missing for this simple low-cost enhancement of Si solar cell efficiency are low-cost high band gap cells.

Influence of sintering temperature, pressing, and conformal coatings on electron diffusion in electrophoretically deposited porous TiO2

The electrophoretic deposition of nanoporous TiO2 layers allows us to investigate separately the influence of sintering temperature, porosity, and conformal surface coatings on the effective diffusion coefficient (Deff) of excess electrons in porous layers. Photocurrent transients were measured to obtain Deff in nanoporous TiO2 layers immersed in aqueous electrolyte. The applied treatments control parameters such as the contact between interconnected nanoparticles, the coordination of nanoparticles in the porous network, and the surface passivation of TiO2 nanoparticles. The hierarchy of the different factors for transport optimization in porous TiO2 is discussed. Under fixed geometry of the nanoporous network, trapping on surface states can strongly limit electron diffusion in porous TiO2.