Flexible photovoltaic cells and modules formed using foils

#The invention relates generally to the field of photovoltaic devices, and more specifically to structures and methods for forming flexible photovoltaic cells and modules.

#Thin film solar cells composed of percolating networks of liquid electrolyte and dye-coated sintered titanium dioxide were developed by Dr. Michael Gratzel and coworkers at the Swiss Federal Institute of Technology. These photovoltaic devices fall within a general class of cells referred to as dye-sensitized solar cells (“DSSCs”). Conventionally, fabrication of DSSCs requires a high temperature sintering process (>about 400° C.) to achieve sufficient interconnectivity between the nanoparticles and enhanced adhesion between the nanoparticles and a transparent substrate. Although the photovoltaic cells of Grätzel are fabricated from relatively inexpensive raw materials, the high temperature sintering technique used to make these cells limits the cell substrate to rigid transparent materials, such as glass, and consequently limits the manufacturing to batch processes and the applications to those tolerant of the rigid structure.

#The invention, in one embodiment, addresses the deficiencies of the prior art by providing methods and structures for forming flexible photovoltaic cells and modules. More particularly, an interconnected photosensitized nanoparticle material is formed on a metal foil that is resistant to high-temperature sintering techniques, unlike flexible substrates that deform at high temperatures. The metal foil is then disposed between two flexible substrates to complete the flexible photovoltaic cell or module.

#The foregoing and other objects, features, and advantages of the invention described above will be more fully understood from the following description of various illustrative embodiments, when read together with the accompanying drawings. In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, and emphasis instead is generally placed upon illustrating the principles of the invention.

#FIG. 1 depicts an exemplary chemical structure of an illustrative embodiment of a polylinker for nanoparticles of an oxide of metal M, in accordance with the invention;

#FIG. 2 depicts another exemplary chemical structure of an illustrative embodiment of a polylinker, according to the invention, for nanoparticles of an oxide of metal M;

#A. Low Temperature Interconnection of Nanoparticles

#As discussed in the summary above, the invention, in one embodiment, provides a polymeric linking agent (hereinafter a “polylinker”) that enables the fabrication of thin film solar cells at relatively low “sintering” temperatures (<about 300° C.). Although the term “sintering” conventionally refers to high temperature (>about 400° C.) processes, as used herein, the term “sintering” is not temperature specific, but instead refers generally to the process of interconnecting nanoparticles at any suitable temperature. In one illustrative embodiment, the invention provides a method for using polylinkers to interconnect nanoparticles in a thin film solar cells. According to another illustrative embodiment, the relatively low temperature sintering process enables the manufacture of such photovoltaic cells using flexible polymer substrates. By employing flexible substrates, the invention also enables a continuous roll-to-roll or web manufacturing process to be employed.

#FIGS. 1 and 2 schematically depict chemical structures of illustrative polylinkers, according to the invention. The particular polylinker structures depicted are for use with nanoparticles of the formula MxOy, where M may be, for example, titanium (Ti), zirconium (Zr), tungsten (W), niobium (Nb), lanthanum (La), tantalum (Ta), terbium (Tb), or tin (Sn) and x and y are integers greater than zero. According to the illustrative embodiment of FIG. 1, the polylinker 100 includes a backbone structure 102, which is similar in structure to the metal oxide nanoparticles, and (OR)i reactive groups, where R may be, for example, acetate, an alkyl, alkene, alkyne, aromatic, or acyl group; or a hydrogen atom and i is an integer greater than zero. Suitable alkyl groups include, but are not limited to, ethyl, propyl, butyl, and pentyl groups. Suitable alkenes include, but are not limited to, ethene, propene, butene, and pentene. Suitable alkynes include, but are not limited to, ethyne, propyne, butyne, and pentyne. Suitable aromatic group include, but are not limited to, phenyl, benzyl, and phenol. Suitable acyl groups include, but are not limited to, acetyl and benzoyl. In addition, a halogen including, for example, chlorine, bromine, and iodine may be substituted for the (OR)i reactive groups.