Patent Application
20200185555
Many different types of photo-voltaic cells have been developed, including crystalline silicon, thin film and multi-junction cells. Although these differing types of cells work along broadly similar principles, with photoactive compounds absorbing energy from photons leading to the production of electric power, the specifics vary broadly. In terms of commercialization, as of 2014, crystalline silicone cells were dominant.
Another type of photovoltaic cell, in development as of 2014, was the bulk heterojunction polymer photovoltaic cell. This type of cell included a polymer thin film having an interpenetrating network of a conjugated polymer donor such as poly(3-hexylthiophene-2,5-diyl) (P3HT) and a soluble fullerene acceptor which is typically [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the photoactive layer. It has been observed, for this type of cell that the triplet state exitons were far more numerous and longer lasting than singlet state exitons. Accordingly, it was found that creating a weak magnetic field in the thin film had the effect of lowering the short-circuit current by increasing the population of triplet state exitons. W. F. Zhang, Y. Xu, H. T. Wang, C. H. Xu, S. F. Yang, Sol. Energy Mater. Sol. Cells 95(2011) 2880.
The experimenters who authored the above noted paper, however, took this result to be intimately tied to the exact nature of bulk heterojunction polymer cells, and they do not ever suggest that the result might be broadly generalizable.
Later, another group of researchers experimented with differing magnetic field strengths applied to dye-sensitized TiO2 nanoparticle-based photovoltaic cells. Although power conversion efficiency was improved, it does not appear that the mechanism was the same as for the earlier experiment. The improvement in the Jsc and g observed in the low magnetic field was attributed to slow electron recombination predominantly caused by the variations of the local electronic surface properties of TiO2. Magnetic-field enhanced photovoltaic performance of dye-sensitized TiO2 nanoparticle-based solar cells Fengshi Cai, Shixin Zhang, Shuai Zhou, Zhihao Yuan.
Notably, both of these groups experimented and published results regarding photovoltaic cells that were largely made of an organic colloidal suspension or gel. Researchers far more readily view material of this sort from the point of view of chemistry, as this type of material can be probed and sampled fairly easily, thereby permitting an investigator to gather information regarding the internal dynamics of the material.
Moreover, despite the research noted above, it does not appear that this technology has been commercially utilized to enhance solar powered electricity generation.
The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements.
In a first separate aspect the present invention may take the form of a method of generating electricity from light that utilizes an array of photovoltaic cells, each including a junction between an electron-donating layer, and an electron-accepting layer, and wherein each cell produces a maximum current during exposure to light when it is exposed to a magnetic field having an optimal strength, and wherein the optimal magnetic field strength varies by more than 5% between the photovoltaic cells. For each the cell, a magnetic field is created in an optimal range of magnetic field strength, that is substantially unvarying over the electron donating layer, as the array is being exposed to light.
In a second separate aspect, the present invention may take the form of an electricity generating assembly, having an array of photovoltaic cells, each including a junction between an electron-donating layer, and an electron-accepting layer, and wherein each cell produces a maximum current during exposure to light when it is exposed to a magnetic field having an optimal strength, and wherein the optimal magnetic field strength varies by more than 5% between the photovoltaic cells. For each cell, a magnet creating a magnetic field in an optimal range of magnetic field strength, that is substantially unvarying over the electron donating layer, as the array is being exposed to light.
In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions.
Exemplary embodiments are illustrated in referenced drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.
Many photovoltaic cells function by having an electron-donating layer made of a material. When struck by a photon of correct energy an electron is freed, thereby creating a potential flow of electricity. But the electron and the moiety from which it has been freed are likely to recombine, ending this process. When the electron-donating layer is a solid, the terminology used to describe the phenomenon of the freed electron and the moiety now missing an electron, having its origin in solid state research, is “active electron” and “hole” often referred to as an “exciton.” Terminology varies but when an entity is produced that has an unpaired orbital electron and a free electron, the system is the equivalent of a free radical and a freed electron and is termed a “free radical equivalent” herein.
It is possible for a liquid, colloidal suspension or a gel to demonstrate that the “hole” actually displays the same characteristics, in terms of magnetic precession, as a free radical. In fact, what has been termed a “hole” in solid state research is a “free radical” but has simply not heretofore been recognized as such. Accordingly, a magnetic field that acts to forestall the recombination of free radicals with active electrons will increase the quantity of free electrons available for transport and therefore the efficiency of the photovoltaic cell. In particular a magnetic field that maintains free radicals in the triplet state, which greatly reduces the chance of recombination, will increase the number of active electrons and increase the efficiency of the photovoltaic cell.
Some of the research referenced in the Background section involved the mixing of magnetic particles into a photosensitive layer. This naturally causes a magnetic field that varies with range to the nearest magnetic particle. A magnetic field at the optimal strength that does not vary significantly over the expanse of the electron-donating layer of photosensitive material will yield a greater increase in photovoltaic cell efficiency.
The vast bulk of photo-voltaic cells in operation as of 2014 include an electron-donating layer comprising a silicon based material, such as monocrystalline silicon, polycrystalline silicon (including ribbon silicon) or amorphous silicon. Other materials placed in commercial use, in thin film structures in which the thickness of the electron-donating layer is less than 40 μm and could be as thin as 2 nm, include cadmium telluride (CdTe), copper indium gallium diselenide (CIGS). Amorphous silicon and crystalline silicon is also used in thin film applications.
Referring to
As shown in
In
In one set of embodiments electron-donating layer 30 and electron-accepting layer 34 are both made of similar material, such as crystalline silicon, but where electron donating layer 30 is n-type and electron-accepting layer 34 is p-type. If comprised of crystalline silicon, layers 30 and 34 may be either monocrystalline silicon or polycrystalline silicon. Alternatively layers 30 and 34 are comprised of amorphous silicon or a thin film material such as CdTe or CIGS. In an alternative set of embodiments, the electron-donating layer 30 is comprised of conjugated polymers and the electron-accepting layer 34 is comprised of inorganic nanocrystals. In an alternative preferred embodiment electron-donating layer 30 or electron-accepting layer 32 or both are made of a perovskite.
For each one of the above recited materials, there is a corresponding magnetic field strength that will typically have a value of between 10 and 100 gauss (1 and 10 millitesla) that optimally extends the triplet state lifetimes in free radicals formed in the material. Moreover, manufacturing photovoltaic cells is not 100% repeatable. That is to say, despite best efforts, it appears that it is not possible to produce a sequence of photovoltaic panels wherein each one has the exact same optimum electromagnetic field, because of unavoidable small differences in the physical structure of the photovoltaic cells, on a molecular level. The responsiveness of a photovoltaic cell to an electromagnetic field can be quite specific, with differences noted in current output for changes in magnetic field strength on the order of one-tenth of a Gauss. Accordingly, to achieve the best output from a photovoltaic array, it is necessary to determine the best magnetic field strength for each cell, separately. Pre-knowledge of the cell characteristics can be used to help set the starting part for the calibration routine, but from this starting point steps of magnetic field strength magnitude are taken, with resultant current measured, as light hitting the cell is held constant.
To determine the optimal magnetic field strength an experiment may be configured by taking a photovoltaic cell 10 and placing it between two Helmholtz coils 16, as shown in
Often, electric power is generated by an array of photovoltaic cells, all of apparently identical construction. It is quite difficult, however, to repeatably create photovoltaic cells for which the optimal magnetic field strength is exactly the same. Small differences in doping levels of the electron donating and electron receiving layers can have a significant impact on the optimal magnetic field strength. Accordingly, referring to
While a number of exemplary aspects and embodiments have been discussed above, those possessed of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.
