Microstructured crystalline device in confined space, a dye-sensitized solar cell, and method of preparation thereof
A method of forming an ordered nanorods array in a confined space is used to form a high surface area device where an ensemble of parallel trenches has micrometer dimensions for the width and depth of the trenches, which are decorated with crystalline nanowires radiating from the sidewalls and bases of the trenches. The high surface area device is formed by depositing a conformal crystalline seed coating in the trenches, forming microchannels from these trenches by placing a barrier layer on the open surface of the trenches, contacting the conformal coating with a crystal precursor solution that is caused to flow through the microchannels. In an embodiment, a very high surface area electrode is constructed with ZnO nanowires radiating from the sidewalls and base of trenches formed on a silicon substrate. The device can be a dye-sensitized solar cell.
1. A method of preparing a high surface area device, comprising:
providing a substrate scribed with a multiplicity of trenches, wherein the trenches have widths of 5 to 100 μm;
optionally, forming a conformal coating of an electrically conductive material over the trenches, and, optionally, tops of the trenches, wherein the conformal coating is 5 nm to 10 μm in thickness and occupies 20 percent or less of the width of the trenches;
depositing a conformal seed layer over the trenches on the substrate, wherein the conformal seed layer has a thickness of 1 nm to 5 μm and occupies 5 percent or less of the width of the trenches;
fixing a barrier layer onto the substrate over the open end of the trenches, wherein microchannels are defined by a surface of the barrier layer and the sidewalls and base of the trenches;
forming a plurality of ports contacting the microchannels, wherein at least one first port resides at a first end of the length of the trenches and at least one second port resides at a second end of the trenches; and
imposing a flow of a crystal precursor solution through the micro channel, wherein the microchannels are maintained at a constant temperature during the period of time that the flow is maintained, and wherein crystalline nanorods grow perpendicularly from the sidewalls and base of the trenches from the conformal seed layer.
2. The method according to claim 1 , wherein the substrate is a conductor, semiconductor, or an insulator.
3. The method according to claim 1 , wherein the substrate is silicon.
4. The method according to claim 1 , wherein the barrier layer is a polydimethylsiloxane sheet.
5. The method according to claim 1 , where the conformal seed layer is a metal oxide and depositing is by atomic layer deposition.
6. The method according to claim 5 , wherein the metal oxide is zinc oxide.
7. The method according to claim 6 , wherein the crystal precursor solution comprises a water soluble zinc salt and an amine in water.
8. The method according to claim 7 , wherein the zinc salt is zinc nitrate and the amine is hexamine.
9. The method according to claim 7 , wherein the crystal precursor solution further comprises a crystal growth modifier.
10. The method according to claim 9 , wherein the crystal growth modifier comprises polyethyleneimine and/or ammonium hydroxide.
11. The method according to claim 1 , wherein imposing a flow results from providing a pressure on the crystal precursor solution at a first port and/or reducing a pressure at a second port.
12. The method according to claim 1 , wherein direction of the flow switches from the first port through the second port to from the second port through the first port.
13. The method according to claim 1 , wherein the temperature is above ambient and below the boiling point of the solvent of the crystal precursor solution.
14. The method according to claim 1 , further comprising preheating the crystal precursor solution prior to imposing a flow of the crystal precursor solution.