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Eta

Research

Eta (extremely thin absorber) solar cells belong, as well as dye-sensitized and organic solar cells, to composite solar cells consisting of interpenetrating electron and hole conductors between which an absorber is sandwiched. The challenge of the Eta concept is to realize inorganic charge selective systems in a complex field of parameters including combination of materials, surface chemistry, local geometry and morphology. Fundamental processes of charge separation, surface passivation, charge transport and recombination are studied in planar and porous model systems. Important technological steps are developed and small-area Eta solar cells are prepared to study their limiting factors.

Content

• Planar Model Systems
• Porous Model Systems
• Solar Cell Structures with Extremely Thin Absorbers (Eta)

Planar Model Systems

Planar model systems allow to study the effects of surface passivation, charge separation mechanisms and transport processes detached from the complex effects that are introduced by porous or nano-structured interfaces. Analyzed materials include dye-sensitized TiO₂ layers, Pt/TiO₂/Ti Schottky diodes, as well as inorganic or organic layers and other metal oxides.

Th. Dittrich, V. Zinchuk, V. Skryshevskyy, I. Urban, O. Hilt, "Electrical transport in passivated Pt / TiO2 / Ti Schottky-diodes", J. Appl. Phys. 98 (2005) 104501.

Th. Dittrich, H.-J. Muffler, M. Vogel, T. Guminskaya, A. Ogacho, A. Belaidi, E. Strub, W. Bohne, J. Röhrich, O. Hilt, M. Ch. Lux-Steiner, "Passivation of TiO₂ by ultra-thin alumina", Appl. Surf. Sci. 240 (2005) 236-243.

Th. Dittrich, "Retarded surface photovoltage response from dye molecules adsorbed on metal oxide surfaces", phys. stat. sol. (a) 201 (2004) R69-R71.

Porous Model Systems

Porous model systems are used to study charge carrier transport mechanisms and the role of the geometry. The focus lies on dye-sensitized porous TiO₂ layers in electrolyte and gas atmospheres. Idealized solar cells with nano-composites are studied to gain knowledge about absorption, charge separation, transport and recombination processes. Employed materials, geometry and dimensions of the structures and the nature of the interfaces are important factors that determine the performance of the solar cell.

S. Tirosh, Th. Dittrich, A. Ofir, L. Grinis, A. Zaban, "Influence of ordering in porous TiO₂ layers on electron diffusion”, J. Phys. Chem. B Letters 110 (2006) 16165-16168.

Th. Dittrich, A. Ofir, S. Tirosh, L. Grinis, A. Zaban, "Influence of the porosity on diffusion and lifetime in porous TiO₂ layers”, Appl. Phys. Lett., 88 (2006) 182110.

Th. Dittrich, I. Mora-Seró, G. Garcia-Belmonte, J. Bisquert, "Temperature dependent normal and anomalous diffusion in porous TiO₂ studied by transient surface photovoltage”, Phys. Rev. B., 73 (2006) 045407. Virtual Journal of Nanoscale Science & Technology 13 (3) (2006).

Solar Cell Structures with Extremely Thin Absorbers(Eta)

The concept of the Eta solar cell was already proposed by Könenkamp in 1998. The Eta (extremely thin absorber) solar cell consists of an extremely thin absorber enclosed between charge selective electron and hole conductors. This gives the opportunity to use semiconductors with very low diffusion length for the absorber. Since the absorber is thin in comparison to the absorption length of the bulk semiconductor, the internal surface area has to be folded in order to increase the amount of material for absorption. This leads to the formation of a nano-composite and opens additionally opportunities for photon management. Eta solar cells promise to be very cost-efficient since low-cost technologies can be applied. Applied materials are, for example, TiO₂ or ZnO as electron conductors, PEDOT:PSS or CuSCN as hole conductors and sulfide layers as absorber.

S. Gavrilov, I. Oja, B. Lim, A. Belaidi, W. Bohne, E. Strub, J. Röhrich, M-Ch. Lux-Steiner, Th. Dittrich, "Charge selective contact on ultra-thin In(OH)_xS_y/Pb(OH)_xS_y heterostructure prepared by SILAR“, phys. stat. sol. (a) 203 (2006) 1024-1029.

I. Oja, A. Belaidi, L. Dloczik, M-Ch. Lux-Steiner, Th. Dittrich, "Photoelectrical properties of In(OH)_xS_y/PbS(O) structures deposited by SILAR on TiO₂“, Semicond. Science & Technol. 21 (2006) 520-526.