Hybrid solar cells with thermal deposited semiconductive...

Details Hybrid solar cells with thermal deposited semiconductive... Hybrid solar cells with thermal deposited semiconductive...

2001-11-21

2004-03-16

Diamond, Alan (Department: 1753)

Batteries: thermoelectric and photoelectric

Photoelectric

Cells

C136S252000, C136S256000, C257S043000, C257S431000, C438S085000, C438S098000, C438S057000

Reexamination Certificate

active

06706962

ABSTRACT:

DESCRIPTION
The present invention is related to the manufacture of organic hybrid solar cells in which the semiconductive oxide layer of the organic hybrid cell is vapour deposited.
Among chief materials used in the past for solar cells have been inorganic semiconductors made from, for example, silicon. However, such devices have proven to be very expensive to construct, due to the melt and other processing techniques necessary to fabricate the semiconductor layer.
In an effort to reduce the cost of solar cells, organic photoconductors and semiconductors have been considered, due to their inexpensive formation by, e.g. thermal evaporation, spin coating, self-assembly, screen printing, spray pyrolysis, lamination and solvent coating. The most often followed strategies in this field can be summarised as follows:
All-organic solar cells produced by vapour deposition are known in the literature. For example, Tang (Tang, Two-layer organic photovoltaic cell, Appl. Phys. Lett. 48(2) (1986) 183-5) reported about organic thin two layer solar cells showing the following structure:
Substrate+ITO/CuPc (30 nm)/ST2(50 nm)/Ag
in which ITO is indium tin oxide, CuPc is copper-phtalocyanine, ST2 is a dye and in which all organic layers were deposited by evapouration. The deposition by evapouration required source temperatures of about 500 and 600° C., respectively, which the substrate was maintained nominally at room temperature during deposition. The resulting cell is herein designated as “Tang cell”. The Tang cell does not include an additional semiconducting oxide layer (SOL) and has an efficiency of 0.96%.
Similarly, Wöhrle et al. and Takahashi et al. reported about organic two and three layer solar cells which were prepared by vapour deposition and/or spin-coating (Wöhrle D., Tennigkeit B., Elbe J., Kreienhoop L., Schnurpfeil G.: Various Porphyrins and Aromatic Terracarbxcylic Acid Diimides in Thin Film p
-Solar cells, Molecular Crystals and Liquid Crystals 230 (1993B) 221-226 Takahashi, K.; Kuraya, N.; Yamaguchi, T.; Komura, T.; Murata, K. Three-layer organic solar cell with high-power conversion efficiency of 3.5%, Solar Energy Materials & Solar Cells 61 (2000) 403-416). These all organic cells do not contain an SOL layer.
Petrisch and co-workers (Petrisch et al. Dye-based donor/acceptor solar cells, Solar Energy Materials & Solar Cells 61 (2000) 63-72) reported about organic solar cells consisting of three dyes, in particular a perylene-tetracarboxylic acid-bis imide with aliphatic side chains (perylene), a metal-free phtalocyanine with aliphatic side chains (HPc). The materials are soluble which allowed cell performance other than vapour depoition (Yu G., Gao J., Hummelen J. C., Wudl F., Heeger A. J.: Polymer Photovotaic Cells: Enhanced Efficiencies via a network of Internal Donor-Acceptor Heterojunctions, Science 270 (1995) 1789-1791.).
Further, laminated cells or cells containing mixtures of donor and acceptor materials (polymers) were also reported by Friend et al. (Friend et al., Nature 397 (1999) 121; Granström et al., Nature 395 (1998) 257-260) and Sariciftici et al. (Sariciftici et al. Science 258 (1992) 1474). Schön et al. (Schön et al. Nature 403 (2000) 408-410) reported on the use of single crystals of organic material as doped pentacene having an efficiency of up to 2.4%. Most of the organic solar cells showing a higher efficiency use I
2
/I
3
−
as a doping system, which is unstable with time.
The use of porous nanocrystalline TiO
2
layers in solar cells is further known from WO 91/16719, EP-A-0 333 641 and WO 98/48433 as well as from other publications of Grätzel et al. (Bach U., Lupo D., Comte P., Moser J. E., Weissortel F., Solbeck J., Spreitzer H., Gratzel M.: Solid state dye-sensitized porous nanocrystalline TiO
2
solar cells with high photon-to-electron conversion efficiencies, Nature 395 (1998) 583-585. Bach U., Grätzel M., Salbeck J., Weissortel F., Lupo D.: Photovoltaic Cell, Brian O'Regan and Michael Grätzel: A low cost, high-efficiency solar cell based on de-sensitized colloidal TiO
2
films, Nature 353, (1991) 737-740.) These cells have efficiencies between 0.74% (for the solid state solar cells) and 7.1% (for the liquid hybrid solar cell). Nevertheless, as pointed out by the authors themselves, the liquid cells described in this publications are difficult to produce and have a reduced longterm stability, whilst the solid cells described have a low efficiency. Furthermore, the porous nano-crystalline TiO
2
layer preparation requires high temperature sintering with temperatures of 450° C.
U.S. Pat. No. 3,927,228 to Pulker describes a method of depositing titanium dioxide layers by evaporation of a molten titantium-oxygen phase. The method of producing TiO
2
layers comprises evaporating a molten titanium-oxygen having a composition corresponding to a proportion of the number of oxygen atoms to the number of titanium atoms of from 1.6 to 1.8, and condensing the vapour on a layer support in the presence of oxygen. The use of this method for the production of solar cells is not disclosed or proposed.
Therefore, most organic/hybrid solar cells known so far show either a low efficiency, a small longterm stability, or they are not suitable to be transferred on flexible substrates. Further, it is still difficult to produce hybrid organic solar cells on large sized carrier substrates.
It is therefore an object of the present invention to provide a solar cell which is both inexpensive to produce and sufficiently efficient as to be useful in terrestrial applications.
It is a related object of the invention to provide a method for the production of a thin, high efficient hybrid solar cell, which can be produced on flexible substrates.
This problem is solved by a method for the production of a hybrid organic solar cell in which the semiconducting oxide layer (SOL) is introduced by thermal deposition. Preferably, the SOL layer is vapour deposited.
The addition of the additional SOL layer can be used to improve the efficiency of known organic solar cells, e.g. the ones as reported by Friend et al. (Friend et al., Nature 397 (1999) 121; Granstrom et al., Nature 395 (1998) 257-260).
The problem of the invention is further solved by a method for the production of a hybrid organic solar cell having the general structure
Substrate+EM/HTM/dye/SOL/EM, or
Substrate+EM/SOL/dye/HTM/EM, or
Substrate +EM/HTM/SOL/EM, in which
EM is the electrode material, selected from the group comprising of a transparent conductive oxide (TCO) and metal, with at least one of the EM layers of the cell being a TCO,
HTM is the hole transport material,
SOL is a semiconducting oxide layer,
“dye” means a suited dye, for example, derivatives of perylenes, and in which the SOL layer of the hybrid solar cell is vapour deposited.
The additional layer of SOL enhances the electron transport to the anode and therefore increases the efficiency of the hybrid organic solar cell according to the invention in comparison with all-organic thin layer solar cells, like the above-mentioned “Tang cell”. The method according to the invention provides a solar cell which is both inexpensive to produce and sufficiently efficient as to be promising in view of future terrestrial applications.
The problem of the invention is further solved by a method for the production of a hybrid organic solar cell having the general structure
Substrate+EM/HTM/dye/SOL/EM, or
Substrate+EM/SOL/dye/HTM/EM, or
Substrate+EM/HTM/SOL/EM, in which
at least one second layer of the hybrid organic solar cell in addition to the SOL layer is applied by vapour deposition.
The multilayer strategy of the present invention is a promising alternative to the expensive production of solar cells based on single crystal and polycrystalline materials, and a new alternative to the known strategies in the filed of organic solar cells and hybrid solar cells. All other layers of the hybrid organic solar cell can be applied by conventional techniques, e.g. thermal evaporation, spin coating, self-assembly, screen printing, spra

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