Solar cell structures using porous column TiO2 films deposited by CVD

Abstract

A method of fabricating a photovoltaic cell for use in a solar cell structure includes preparing a first substrate; preparing a TiO2 precursor; preparing a cold wall CVD chamber; placing the first substrate in the cold wall CVD chamber; forming a transparent conducting electrode on the first substrate; depositing a porous column TiO2 film on the transparent conducting electrode; depositing a photosensitive material in and on the porous column TiO2 film; forming a top electrode on the photovoltaic cell; and incorporating the photovoltaic cell into a solar cell structure. The method of the invention is suitable for forming photovoltaic cells which may be of the dye-sensitized solar cell (DSSC) type, having a liquid or solid-state electrolyte therein, or an ordered organic-inorganic heterojunction photovoltaic cell.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the method of the invention.

FIG. 2 depicts a DSSC photovoltaic cell having a porous column TiO₂ film therein.

FIG. 3 depicts an ordered organic-inorganic heterojunction photovoltaic cell having a porous column TiO₂ film therein.

FIG. 4 is a SEM photo of a porous column TiO₂ film.

FIG. 5 is a SEM photo of a different morphology of a porous column TiO₂ film.

FIG. 6 is an XRD spectrum of a porous column TiO₂ film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

We have successfully grown high density porous column TiO₂ structures wherein the pore extend normal to the substrate, and extend directly from the top of the film to the bottom of the film. The method of the invention is depicted generally at 10 in FIG. 1. A first substrate is prepared, 12. In the preferred embodiment, the substrate is a glass or plastic substrate. A precursor is prepared, 14, which, in the preferred embodiment, is titanium isopropoxide (Ti (OC₃H₇)₄).

Preparation of a cold wall CVD chamber 16 includes maintaining both the precursor and the transport line at a temperature of between about 20° C. to 80° C. The substrate temperature is maintained between about 200° C. to 800° C.; and the pressure in the CVD chamber is maintained in the range of between about 1 torr. to standard atmosphere; The reaction gas is oxygen and the carrier gas is argon. Alternatively, other inert gases, such as nitrogen, may be used as the carrier gas. The cold wall CVD chamber has the first substrate placed therein, 18. The chamber is vacated to below 1 mtorr., and then oxygen or an oxygen and argon mixture is used to fill the chamber to the required growth pressure. The carrier gas flow and oxygen flow are in the range of between about 1 sccm to 1000 sccm.

The fabrication process for a photovoltaic cell follows the method of the invention, which provides fabrication techniques for a variety of photovoltaic cells, all of which use a porous column TiO₂ film as a support structure for various photosensitive materials. Once the deposition parameters are set in the CVD chamber, a transparent conducting electrode is formed 20 on the first substrate. The transparent conducting electrode may be formed of indium-tin-oxide (ITO) or SnO₂:F, deposited to a thickness of between about 10 nm to 1000 nm by CVD, PVD, spin-coating or electroplating. Next, a porous column TiO₂ film is deposited by CVD 22 to a thickness of between about 100 nm to 50 μm.

Once the porous column TiO₂ film is deposited, the stage is set for fabrication of a photovoltaic cell, which may be of the dye-sensitized solar cell (DSSC) type, having a liquid or solid-state electrolyte therein, or an ordered organic-inorganic heterojunction photovoltaic cell, as depicted by the three branches in FIG. 1. Common to the three embodiments of the method of the invention, a photosensitive material is deposited in and on the porous column TiO₂ film.

One form of the method of the invention includes sensitization 24 of the TiO₂ film using cis-RuL₂ (NCS)₂, or other suitable dye sensitizers.

When a liquid electrolyte is used with the DSSC, a top electrode is formed 26 on a second substrate. The top electrode is then placed in contact with the sensitized porous column TiO₂ film. The edge of the combined structure is sealed 30, and the space between the top and the bottom electrodes is filled 32 with a liquid electrolyte, such as lodolyte, an iodide-based redox electrolyte, to complete the cell.

When a solid-state electrolyte is used, such as spiro-MeOTAD, it may be deposited 34 on the sensitized porous column TiO₂ film by spin coating, CVD, screen printing, or any other state-of-the-art technique. A top electrode is formed 36 on the solid state electrolyte to complete the photovoltaic cell.

Alternatively, for an ordered organic-inorganic heterostructure photovoltaic cell, after step 22, a light absorbing conjugated polymer, such as P3HT, is deposited 40 and a top electrode is formed 42 to complete the photovoltaic cell.

Referring now to FIG. 2, a DCCS photovoltaic cell is depicted generally at 50. The first substrate 52 is prepared according to the method of the invention, a transparent conductive electrode 54 formed thereon. The porous column TiO₂ film 56 is deposited by CVD. An electrolyte 58, either liquid or solid-state, is formed in the photovoltaic cell, as previously described. In this embodiment, a layer 59 of cis-RuL₂ (NCS)₂ is formed on porous column TiO₂ film 56. Top electrode 60 is formed.

FIG. 3 depicts an ordered organic-inorganic heterojunction photovoltaic cell at 70, which includes the same components as DCCS photovoltaic cell 50, except that the electrolyte is replaced by a light absorbing conjugated polymer 72.

FIGS. 4 and 5 depict SEM photos of porous column TiO₂ structures, depicting different morphologies of the TiO₂ column structure. FIG. 6 is an XRD spectrum of the fabricated layer, which confirmed that the film is anatase TiO₂.

Thus, a method for fabricating a porous column TiO₂ film photovoltaic cell has been disclosed. It will be appreciated that further variations and modifications thereof may be made within the scope of the invention as defined in the appended claims.

Claims

1. A method of fabricating a photovoltaic cell for use in a solar cell structure comprising: preparing a first substrate;preparing a TiO2 precursor;preparing a cold wall CVD chamber;placing the first substrate in the cold wall CVD chamber;forming a transparent conducting electrode on the first substrate;depositing a porous column TiO2 film on the transparent conducting electrode;depositing a photosensitive material in and on the porous column TiO2 film;forming a top electrode on the photovoltaic cell; andincorporating the photovoltaic cell into a solar cell structure.

2. The method of claim 1 wherein said depositing a photosensitive material in and on the porous column TiO2 film includes depositing a dye sensitizer on the porous column TiO2 film.

3. The method of claim 2 which includes forming a top electrode on a second substrate, sealing the top electrode to the porous column TiO2 film, and filling the photovoltaic cell with a liquid electrolyte.

4. The method of claim 2 which includes depositing a solid-state electrolyte in and on the porous column TiO2 and forming a top electrode on the solid-state electrolyte.

5. The method of claim 1 wherein said depositing a photosensitive material in and on the porous column TiO2 film includes depositing a light absorbing conjugated polymer in and on the porous column TiO2 and forming a top electrode thereon.

6. The method of claim 1 wherein said preparing a first substrate includes preparing a substrate taken from the group of substrates consisting of glass and plastic.

7. The method of claim 1 wherein said preparing a TiO2 precursor includes preparing a titanium isopropoxide (Ti(OC3H7)4) precursor.

8. A method of fabricating a photovoltaic cell for use in a solar cell structure comprising: preparing a first substrate taken from the group of substrates consisting of glass and plastic;preparing a titanium isopropoxide (Ti(OC3H7)4) precursor to form a TiO2 film;preparing a cold wall CVD chamber;placing the first substrate in the cold wall CVD chamber;forming a transparent conducting electrode on the first substrate;depositing a porous column TiO2 film on the transparent conducting electrode;depositing a photosensitive material in and on the porous column TiO2 film;forming a top electrode on the photovoltaic cell; andincorporating the photovoltaic cell into a solar cell structure.

9. The method of claim 8 wherein said depositing a photosensitive material in and on the porous column TiO2 film includes depositing a dye sensitizer on the porous column TiO2 film, wherein the dye sensitizer is cis-RuL2(NCS)2.

10. The method of claim 9 which includes forming a top electrode on a second substrate, sealing the top electrode to the porous column TiO2 film, and filling the photovoltaic cell with a liquid electrolyte, wherein the liquid electrolyte is lodolyte

11. The method of claim 9 which includes depositing a solid-state electrolyte in and on the porous column TiO2 and forming a top electrode on the solid-state electrolyte, wherein the solid-state electrolyte is spiro-MeOTAD.

12. The method of claim 8 wherein said depositing a photosensitive material in and on the porous column TiO2 film includes depositing a light absorbing conjugated polymer in and on the porous column TiO2 and forming a top electrode thereon, wherein the light absorbing conjugated polymer is P3HT.