CN101411001A - Nanoparticle sensitized nanostructured solar cells - Google Patents

Abstract

This invention provides a solar cell with a nanoparticle-sensitized nanostructure. This invention relates to the field of photovoltaics or solar cells. More specifically, this invention relates to photovoltaic devices using metal oxide nanostructures and photosensitive nanoparticles comprising nanoparticles of different sizes and compositions to form photovoltaic devices.

Description

Nanoparticle-sensitized nanostructured solar cells

technical field

In general, the present invention relates to the field of photovoltaic cells or solar cells. More specifically, the present invention relates to photovoltaic devices using nanostructures with nanoparticles comprising different sizes and different compositions to form photosensitive nanoparticles of photovoltaic devices.

Background technique

Rising oil prices have increased the importance of developing cost-effective renewable energy sources. Significant efforts are underway worldwide to develop cost-effective solar cells to harvest solar energy. Current solar technologies can be mainly classified into crystalline silicon and thin film technologies. More than 90% of solar cells are manufactured from silicon - monocrystalline, polycrystalline or amorphous.

Historically, crystalline silicon (c-Si) has been used as a light-absorbing semiconductor in most solar cells, although it is a relatively poor light absorber and requires considerable thickness (hundreds of micrometers) of material. However, it proves convenient because it gives stable solar cells with good efficiencies (12-20%, half to two-thirds of the theoretical maximum) and uses knowledge bases from the microelectronics industry. ) process technology developed in.

Two types of crystalline silicon are used industrially. The first is monocrystalline silicon, which is manufactured by cutting wafers (approximately 150 mm in diameter and 350 microns thick) from a high purity single crystal boule. The second is polysilicon, which is manufactured by cutting a cast block of silicon first into bars and then into wafers. The main trend in the manufacture of crystalline silicon cells is to develop towards polycrystalline technology. For monocrystalline and polycrystalline silicon, semiconductor p-n junctions are formed by diffusing phosphorus (n-type dopant) into the top surface of a boron-doped (p-type) Si wafer. Screen printed contacts are applied to the front and back of the cell, the front contact pattern is specifically designed to allow maximum light exposure to the silicon material with minimal electrical (resistive) loss in the cell.

Silicon solar cells are very expensive. Manufacturing matures but does not bring significant cost reductions. Silicon is not an ideal material for use in solar cells because it primarily absorbs in the visible region of the solar spectrum, limiting conversion efficiency.

Second-generation solar cell technology is based on thin films. The two main thin film technologies are amorphous silicon and CIGS.

Amorphous silicon (a-Si) was considered the only thin-film photovoltaic (PV) material in the 1980s. But at the end of that decade and in the early 1990s, it was abandoned by many researchers due to its low efficiency and instability. However, amorphous silicon technology has made good progress in developing a very sophisticated (sophisticated) solution to these problems: the multijunction configuration. Today, commercial multi-junction a-Si modules can have efficiencies in the range of 7%-9%. United Solar System Corporation and Kanarka plans to build 25MW fabrication facilities, and several companies have announced plans to build fabrication plants in Japan and Germany. BP Solar and United Solar System Corporation plan to build a 10MW facility in the near future.

The key barriers to a-Si technology are low efficiency (about 11% stable), light-induced efficiency degradation (which requires more complex cell designs, such as multiple junctions), and process cost (manufacturing methods are based on vacuum and rather slowly). All of these issues are important to the potential to fabricate cost-effective a-Si modules.

Thin-film solar cells made of copper indium gallium selenide (CIGS, Copper Indium Gallium Diselenide) absorbers are expected to achieve high conversion efficiencies of 10-12%. The record high efficiency (19.2% NREL) of CIGS solar cells is by far the highest compared to those achieved by other thin film technologies such as cadmium telluride (CdTe) or amorphous silicon (a-Si).

These record-breaking small-area devices have been fabricated using capital-intensive and very expensive vacuum evaporation techniques. It is very challenging to fabricate CIGS films with uniform composition on large-area substrates. This limitation also affects the often very low process yields. Due to these limitations, the implementation of evaporation technology has not been successful in the large-scale, low-cost commercial production of thin-film solar cells and modules and cannot compete with today's crystalline silicon solar modules.

To overcome the limitations of PVD technology using expensive vacuum equipment, several companies have developed high-throughput vacuum processes (eg: DayStar, Global Solar) and non-vacuum processes (eg: ISET, Nanosolar) for manufacturing CIGS solar energy Battery. Using ink technology, very high active material utilization can be achieved at relatively low capital equipment costs. The combined effect is a low-cost manufacturing process for thin-film solar devices. CIGS can be fabricated on flexible substrates, which makes it possible to reduce the weight of solar cells. CIGS solar cells are expected to cost less than crystalline silicon, making them competitive even at lower efficiencies. The two main problems with CIGS solar cells are: (1) there is no clear path to higher efficiencies; and (2) the high processing temperatures make it difficult to use high-speed roll toroll processes, so they cannot achieve significant lower cost structure.

These are significant problems with currently available technology. Crystalline silicon solar cells, which now have a market share of greater than 90%, are very expensive. Crystalline silicon solar cells that harness the sun's energy cost about 25 cents/kWh, compared to less than 10 cents/kWh for fossil fuels. In addition, the capital cost of installing solar panels is very high and limits its adoption rate. Crystalline solar cell technology is mature and is unlikely to improve performance or cost competitiveness in the near future. Amorphous silicon thin-film technology is suitable for high-volume manufacturing, which enables low-cost solar cells. Furthermore, amorphous silicon and microcrystalline silicon solar cells only absorb in the visible region.

Next-generation solar cells need to be truly high-efficiency as well as light-weight and low-cost. Two potential candidates are (1) polymer solar cells and (2) nanoparticle solar cells. Polymer solar cells have the potential to be low cost due to the winding process at moderate temperatures (<150°C). However, polymers have two major disadvantages: (1) low efficiency due to slow charge transport; and (2) poor stability - especially to ultraviolet light (UV). It is therefore unlikely that polymer solar cells will be able to achieve the properties needed to be the next generation of solar cells. The most promising technology for next-generation solar cells is based on quantum dot (QD, quantum dot) nanoparticles.

Several research groups have carried out experimental studies of quantum dot based solar cells. Most commonly used quantum dots are made of compound semiconductors such as groups II-VI, II-IV and III-V. Some examples of these photosensitive quantum dots are CdSe, CdTe, PbSe, PbS and ZnSe.

Solar cells made from photosensitive nanoparticles described in the art exhibit very low efficiencies (<5%). Nanoparticles are very efficient at generating electron-hole charge pairs when exposed to sunlight. The main reason for these inefficiencies is charge recombination. To achieve high efficiency in solar cells, charges must be separated as soon as they are generated. The recombined charges do not generate any photocurrent and thus do not contribute to the efficiency of the solar cell. Charge recombination in nanoparticles is mainly due to two factors: (1) surface states on the nanoparticles that facilitate charge recombination; and (2) slow charge transport. In the latter case, charge recombination is generally faster compared to the rate of charge transport because the charge passes slowly through the electron transport layer and the hole transport layer.

Various approaches have been reported in the prior art to address these issues with nanoparticles. Surface treatment techniques have been attempted to remove surface states. (See Furis et al., MRS Proceedings, volume 784, 2004) These techniques show improvements in photoluminescence but do not improve solar conversion efficiency, since they do not affect the charge transport properties of the hole transport layer and the electron transport layer.

It is known in the art that _TiO2 layers can be used for fast electron transport. Dye-sensitized solar cells use TiO ₂ for this reason. Transparent TiO ₂ nanotubes have been reported in the literature (Mor et al., Adv. Funct. Mater., 2005, 15, 1291-1296 (2005)). These _TiO2 nanotubes have been used to prepare dye-sensitized solar cells.

Contents of the invention

The photovoltaic device includes a first electrode and a second electrode, at least one of which is transparent to solar radiation. The first layer including the electronically conductive nanostructures is in electrical communication with the first electrode. A photoactive layer comprising photosensitive nanoparticles is located adjacent to the electronically conductive nanostructures. The hole transport layer is in contact with the photoactive layer and the second electrode. A blocking layer may also be included between the hole transport layer and the first electrode.

The electron conducting nanostructures may be nanotubes, nanorods or nanowires. Preferred nanotubes are made of _TiO2 . Preferred nanowires are made of ZnO.

The photosensitive nanoparticles can be quantum dots, nanorods, nanobipods, nanotripods, nanomultipods or nanowires. In some cases, the photosensitive nanoparticles are covalently attached to the nanostructures. Preferred photosensitive nanoparticles include CdSe, ZnSe, PbSe, InP, PbS, ZnS, Si, Ge, SiGe, CdTe, CdHgTe or group II-VI, II-IV or III-V materials. In some embodiments, first and second nanoparticles that absorb radiation from different parts of the solar spectrum are used in a photovoltaic device. The first and second nanoparticles may differ in composition, size, or a combination of size and composition.

In another embodiment, the second photoactive layer is used containing nanoparticles that absorb radiation from a different part of the solar spectrum than the nanoparticles of the first layer. The nanoparticles in the first photoactive layer and the second photoactive layer can differ in composition, size, or a combination of size and composition.

In some embodiments, the hole transport layer is a hole transporting polymer such as a p-type semiconducting polymer. Examples of p-type semiconducting polymers include P3HT, P3OT, MEH-PPV or PEDOT. In other embodiments, the hole transport layer is a p-type semiconductor. Examples of p-type semiconductors include p-doped Si, p-doped Ge, or p-doped SiGe. In the case of Si, the p-type semiconductor may be p-doped amorphous silicon, p-doped microcrystalline silicon or p-doped nanocrystalline silicon. In some cases, the hole transport layer is made of two or more layers of p-type semiconductors. The p-type semiconductor layer may be a p-doped silicon layer, a p-doped germanium layer and/or a p-doped SiGe layer.

A photovoltaic device may be fabricated by forming a first layer comprising electronically conductive nanostructures on a first electrode such that the first layer is in electrical communication with the first electrode. A photoactive layer comprising photosensitive nanoparticles is then formed on the electronically conductive nanostructures. Then, a hole transport layer is formed on the photoactive layer. A second electrode is then built on the hole transport layer. At least one of the first electrode and the second electrode is transparent to solar radiation. A blocking layer may also be incorporated before the nanostructure or hole transport layer is formed. The photoactive layer can be made with different nanoparticles to create a random distribution of different nanoparticles in the layer. In another embodiment, the photoactive layer is made of at least two layers of different nanoparticles. In this case, the method includes forming a layer of first nanoparticles on the nanostructure and forming a layer of second nanoparticles on the layer of first nanoparticles.

Description of drawings

Figure 1 (Prior Art) shows nano quantum dots of different sizes absorbing and emitting radiation with different colors. Small dots absorb at the blue end of the spectrum while larger sized dots absorb at the red end of the spectrum.

Figure 2 (Prior Art) shows UV, visible and infrared (IR) absorbing/emitting quantum dots made of ZnSe, CdSe and PbSe, respectively.

Figure 3 (Prior Art) shows nanoparticles coated with a solvent such as tri-n-octyl phosphine oxide (TOPO).

Figure 4 shows nanoparticles functionalized with R groups. The R group can be represented by X _a -R _n -Y _b , where X and Y are reactions such as carboxylic acid (-COOH) group, phosphoric acid (-H ₂ PO ₄ ) group, sulfonic acid (-HSO ₃ ) group or amine A group, a and b are 0 or 1, wherein one of a and b is 1, R is carbon, nitrogen or oxygen, and n is 0-10 or 0-5.

5A-5F illustrate the formation of a solar cell according to one embodiment. In FIG. 5A, a thin film of titanium is deposited on fluorine-doped tin oxide that has been deposited on a transparent substrate. In Figure 5B, _TiO2 nanotubes on fluorine-doped tin oxide were deposited on a transparent substrate. In Figure 5C, _TiO2 nanotubes bearing hydroxyl functional groups were deposited on fluorine-doped tin oxide that had been deposited on a transparent substrate. In Figure 5D, the nanoparticle sensitizer is attached to the _TiO2 nanotubes. In Figure 5E, a transparent hole transport layer such as ITO, PEDOT, etc. is deposited on the nanoparticle sensitizer. In Figure 5F, an electrode layer (ITO or metal) was deposited _on nanoparticle-sensitized _TiO2 nanotubes on fluorine-doped tin oxide deposited on a transparent substrate.

Figure 6 shows the nanoparticle sensitized solar cell in Figure 5F receiving sunlight (100) to generate a voltage.

Figure 7 shows another embodiment of a nanoparticle sensitized solar cell with titanium metal foil as substrate and electrodes.

Figure 8 shows a nanoparticle-sensitized solar cell with _TiO2 nanorods on fluorine-doped tin oxide.

Figure 9 shows an alternative embodiment of a nanoparticle-sensitized solar cell with _TiO2 nanorods on titanium metal foil.

Figure 10 shows a broadband embodiment of the solar cell of Figure 6 in which quantum dots of different sizes and/or compositions are randomly distributed on the _Ti02 nanotubes.

Figure 11 shows a broadband embodiment of the solar cell of Figure 7 in which quantum dots of different sizes and/or compositions are randomly distributed on the _TiO2 nanotubes.

Figure 12 shows a broadband embodiment of the solar cell of Figure 9 in which quantum dots of different sizes and/or compositions are randomly distributed on the _TiO2 nanotubes.

Figure 13 shows a broadband embodiment of the solar cell of Figure 8 in which quantum dots of different sizes and/or compositions are randomly distributed on the _TiO2 nanotubes.

Figure 14 shows a broadband embodiment of the solar cell of Figure 6 in which a quantum dot layer of different size and/or composition is located on a _TiO2 nanotube.

Figure 15 shows a broadband embodiment of the solar cell of Figure 7 in which a quantum dot layer of different size and/or composition is located on a _TiO2 nanotube.

Figure 16 shows a broadband embodiment of the solar cell of Figure 8 in which a quantum dot layer of different size and/or composition is located on a _TiO2 nanotube.

Figure 17 shows a broadband embodiment of the solar cell of Figure 9 in which a quantum dot layer of different size and/or composition is located on a _TiO2 nanotube.

Detailed ways

Embodiments of photovoltaic devices disclosed herein consist of two electrodes, a first layer comprising electron-conducting nanostructures, a photoactive layer comprising photosensitive nanoparticles adjacent the electron-conducting nanostructures, and a hole transport layer contacting the photoactive layer. The first layer is electrically connected to the first electrode. The hole transport layer contacts the photoactive layer and the second electrode. At least one of the first electrode and the second electrode is transparent to solar radiation.

As used herein, the term "nanostructure" or "electron-conducting nanostructure" refers to nanotubes, nanorods, nanowires, and the like. Electronically conducting nanostructures are crystalline in nature. Typically, nanostructures are made of semiconductor materials with a wide bandgap, where the bandgap is, for example, 3.2eV for _TiO2 . The nanostructures are chosen such that their bandgap is larger than the largest bandgap of the photosensitive nanoparticles to be used in the solar cell (eg, >2.0eV).

Electronically conductive nanostructures can be made of, for example, titanium dioxide, zinc oxide, tin oxide, indium tin oxide (ITO) and indium zinc oxide. Nanostructures can also be made of other conductive materials such as carbon nanotubes. Nanostructures can be grown directly on metal foils, glass substrates or plastic substrates coated with thin conductive metal or metal oxide films such as fluorine-doped tin oxide. For _TiO2 nanostructures, see e.g. Mor et al., "Use of Highly-Ordered _TiO2 Nanotube Arrays in Dye-Sensitized Solar Cells." Nanoletters Vol.6, No.2, pp.215-218 (2005). Mor et al. al., Nanoletters Vol.5, no.1, pp.191-195(2005); Barghese et al., Journal of Nanoscience and Nanotechnology, no.1, Vol.5, pp.1158-1165(2005); and Paulose et al. Nanotechnology 17, pp. 1-3 (2006). For ZnO nanowires, see Baxter and Aydel, Solar Energy Material and Solar Cells 90, 607-622 (2006); Greene, et al., Angew.Chem.Int.Ed.42, 3031-3034 (2003); and Law , et al., Nature Materials 4, 455-459 (2005).

Electronically conductive nanostructures can be prepared by methods known in the art. For example, _TiO2 nanotubes can be fabricated by anodizing a titanium metal film or anodizing a titanium metal film deposited on fluorine-doped tin oxide. Conductive nanostructures can also be prepared by employing colloidal growth promoted by seed particles deposited on a substrate. Conductive nanostructures can also be prepared by vacuum deposition processes such as chemical vapor deposition (CVD) and metal organic chemical vapor deposition (MOCVD), epitaxial growth methods such as molecular beam epitaxy (MBE), and the like.

In the case of nanotubes, the outer diameter of the nanotubes ranges from about 20 nanometers to 100 nanometers, in some cases from 20 nanometers to 50 nanometers and in other cases from 50 nanometers to 100 nanometers. The inner diameter of the nanotubes can be from about 10 nanometers to 80 nanometers, in some cases from 20 nanometers to 80 nanometers, and in other cases from 60 nanometers to 80 nanometers. The wall thickness of the nanotubes may be 10-25 nanometers, 15-25 nanometers or 20-25 nanometers. In some cases, the nanotubes are 100-800 nanometers, 400-800 nanometers, or 200-400 nanometers in length.

In the case of nanowires, the diameter can be from about 100 nanometers to about 200 nanometers and can be 50-100 microns long. Nanorods can have a diameter from about 2-200 nanometers but are often 5-100 nanometers or 20-50 nanometers in diameter. They may be 20-100 nanometers in length, but are often between 50-500 nanometers or 20-50 nanometers in length.

As used herein, the term "nanoparticle" or "photosensitive nanoparticle" refers to a photosensitive material that generates electron-hole pairs when exposed to solar radiation. The photosensitive nanoparticles are usually nanocrystals, such as quantum dots, nanorods, nanobipods, nanotripods, nanomultipods or nanowires.

Photoactive nanoparticles can be made from compound semiconductors including II-VI, II-IV and III-V materials. Some examples of photosensitive nanoparticles are CdSe, ZnSe, PbSe, InP, PbS, ZnS, CdTe, Si, Ge, SiGe, CdHgTe or group II-VI, II-IV and III-V materials. Photosensitive nanoparticles can be of core type or core-shell type. In core-shell nanoparticles, the core and shell are made of different materials. Both the core and the shell can be made of compound semiconductors.

Quantum dots are the preferred nanoparticles. As is known in the art, quantum dots with the same composition but different diameters absorb and emit radiation at different wavelengths. Figure 1 shows three quantum dots made of the same composition but with different diameters. Small quantum dots absorb and emit in the blue part of the spectrum; whereas, medium and large quantum dots absorb and emit in the green and red parts of the visible spectrum, respectively. Alternatively, as shown in Figure 2, the quantum dots may be of substantially the same size but made of different materials. For example, UV absorbing quantum dots can be made of zinc selenide; whereas, visible and IR quantum dots can be made of cadmium selenide and lead selenide, respectively. Nanoparticles with different sizes and/or compositions can be used randomly or in layers to make broadband solar cells absorbing in (1) UV and visible; (2) visible and IR or (3) UV, visible and IR .

Photoactive nanoparticles can be modified to include linkers X _a -R _n -Y _b , where X and Y can be, for example, carboxylic acid groups, phosphonic acid groups, sulfonic acid groups (sulfonic acid group) or reactive moiety containing amine groups etc., a and b are independently 0 or 1, wherein at least one of a and b is 1, R is such as -CH ₂ , -NH- Or -O- carbon-containing group, nitrogen-containing group or oxygen-containing group, n is 0-10 or 0-5. One reactive group can react with nanoparticles and another reactive group can react with nanostructures. For example, when two layers of nanoparticles are deposited on the nanostructure, the nanoparticles of the base layer can contain linkers with acid functionality capable of forming bonds with the metal oxide nanostructure. The nanoparticles of the second layer may contain basic units such as amine groups or hydroxyl groups to form amide bonds or ester bonds with the acid groups of the first nanoparticle linker. Linkers also passivate the nanoparticles and increase their stability, light absorbing and photoluminescent properties. They can also improve the solubility or suspension of nanoparticles in common organic solvents.

The functionalized nanoparticles react with suitable reactive groups such as hydroxyl groups or others on the nanostructures to deposit a dense and continuous monolayer of nanoparticles by a molecular self assembly process. By adjusting the composition of Xa _{- Rn} - _Yb , the distance between (1) the surface of the nanostructure and the nanoparticle or (2) the nanoparticle and another nanoparticle can be tuned such that the surface promotes charge recombination State effects are minimized. The distance between these surfaces is typically 10 Angstroms or less, preferably 5 Angstroms or less. Maintaining this distance allows electrons to tunnel through this gap from the nanoparticle to the highly conductive nanostructure. This facile electron transport helps reduce charge recombination and leads to efficient charge separation, which will lead to efficient solar energy conversion.

As used herein, a "hole transport layer" is an electrolyte that preferentially conducts holes. The hole transport layer may be (1) an inorganic molecule comprising p-doped semiconductor material such as p-type amorphous or microcrystalline silicon or germanium, (2) such as metal-thalocyanine, arylamine Organic molecules such as (arylamine), and (3) conductive polymers such as polyethylenedioxythiophene (PEDOT), P3HT, P3OT, and MEH-PPV.

A solar cell combining the aforementioned nanostructures, nanoparticles and hole transport layer with at least one first and second electrode transparent to solar radiation is shown in FIG. 6 . This solar cell was fabricated according to the protocol of Example 1 and as outlined in Figures 5A to 5F.

It should be understood that the first layer containing electronically conducting nanostructures is preferably not a continuous layer. Rather, in some cases, the layer is made of spaced apart nanostructures. This allows the introduction of photosensitive nanoparticles between the nanostructures. In this embodiment, the distance between the nanostructures takes into account the size of the nanoparticles and also the number of layers of nanoparticles to be applied to the nanostructures.

Given that the nanoparticles are arranged on the nanostructures, the photoactive layer need not be a uniform layer, as it can conform to all or part of the three-dimensional structure of the nanostructure layer and can be continuous or discontinuous.

Likewise, the hole-transport layer has a structure that conforms to the shape of the underlying solar cell layer and the surface of the electrode in electrical contact therewith. In some embodiments, the hole transport layer is in contact with the photosensitive nanoparticles and the second electrode.

In a preferred embodiment, the barrier layer is arranged between the entire conductive layer and the first electrode. This layer can be fabricated simultaneously during nanostructure formation, for example, when _TiO2 nanotubes are fabricated on titanium foil.

In some embodiments, the solar cell is a broadband solar cell capable of absorbing different wavelengths of solar radiation. The photosensitive nanoparticles generate electron-hole pairs when exposed to light of a specific wavelength. The bandgap of photosensitive nanoparticles can be tuned by changing the particle size or composition of the nanoparticles. By combining a range of nanoparticle sizes with a range of nanomaterials used to make the nanoparticles, broadband absorption of part or the entire solar spectrum can be achieved. Thus, in one embodiment, a mixture of photosensitive nanoparticles of different sizes and/or compositions can be layered on the first layer of nanostructures to fabricate broadband solar devices such as those outlined in FIGS. 11-13 .

Alternatively, nanoparticles of different sizes and/or compositions may individually form multiple layers with each layer responding to a different portion of the solar spectrum. Examples of such solar cells can be found in Figures 14-17. In such embodiments, preferably the nanoparticles are layered such that the layer closest to the nanostructures absorbs radiation at longer wavelengths than the material forming the second layer. If a third layer is present, preferably the second layer absorbs at longer wavelengths than the third layer absorbs, and so on.

Example 1

A nanoparticle sensitized solar cell is shown in FIG. 6 . The key steps necessary to fabricate the solar cell shown in Figure 6 are shown in Figures 5A-5F. By using methods known in the art, a suitable transparent substrate (510) is first coated with a fluorine-doped tin oxide layer (520), followed by deposition of 300 nm to 2 micron thick titanium thin film layer (530). By using methods known in the art, the Ti film (530) is anodized and heat treated to obtain transparent _Ti02 nanotubes (540). Anodization conditions are optimized to obtain a barrier layer (550) that acts like an insulator and prevents shorting of the cathode/anode in the solar cell. The surface of TiO ₂ nanotubes contains hydroxyl (-OH) functional groups (560). Nanoparticles made of luminescent materials such as CdSe, ZnSe, PbSe, InP, PbS, III-V materials with appropriate functional groups (-COOH, -NH ₂ , -PO ₄ or -SO ₃ H) and TiO ₂ nanotubes were reacted to obtain nanoparticle (570) sensitized TiO ₂ nanotubes. As shown in Figure 5D, nanoparticles modify nanotubes by forming monolayers by a molecular self-assembly process. Use solvent washing to remove loosely bound nanoparticles. Since the deposition of nanoparticles on TiO ₂ nanotubes is controlled by the reaction of -OH functional groups on TiO ₂ with nanoparticle functional groups (-COOH, -NH ₂ , -PO ₄ , -SO ₃ H), the nanoparticles The thickness is automatically limited to a few monolayers. Then, a hole transport layer is deposited (580). The hole transport layer can be a polymeric material such as a conductive polymer (eg: PEDOT). Finally electrodes (transparent or translucent) (590) are deposited to complete the cell. If a translucent electrode (590) is deposited, then the cell will be oriented such that sunlight (100) falls on the transparent substrate (510) in FIG. 6 . When sunlight falls on the solar cell shown in Figure 6, electron-hole pairs are generated by the nanoparticles. These nanoparticles can be of various sizes, geometries and compositions to cover the entire solar spectrum. Since the luminescent nanoparticles are directly attached to the electron-conducting _TiO2 nanotubes, easy charge separation occurs thereby minimizing any charge recombination. The solar cell shown in Figure 6 is expected to have high efficiency and be fabricated at low cost relative to other thin film and silicon based technologies.

Example 2

Another embodiment of a nanoparticle sensitized solar cell is shown in FIG. 7 . The key steps necessary to fabricate a solar cell are similar to those shown in Figures 5A to 5F, with the following exceptions. By using methods known in the art, the titanium metal foil (710) is anodized to obtain transparent _Ti02 nanotubes (730). The conditions of anodization are optimized to obtain a barrier layer that acts like an insulator and prevents shorting of the cathode/anode in the solar cell (720). The surface of the TiO ₂ nanotubes (730) contains hydroxyl (-OH) functional groups. Nanoparticles made of luminescent materials such as CdSe, ZnSe, PbSe, InP, PbS, III-V materials with appropriate functional groups (-COOH, -NH ₂ , -H ₂ PO ₄ or -SO ₃ H) The particles are reacted with the _Ti02 nanotubes to obtain nanoparticle (750) sensitized _Ti02 nanotubes. Then, a hole transport layer is deposited (760). The hole transport layer may be a polymeric material such as a conductive polymer, eg PEDOT. Finally a transparent conductive oxide layer (770) is deposited to complete the cell. The solar cells are oriented such that sunlight (780) falls on the transparent conductive oxide layer (770). The solar cell shown in Figure 7 is expected to have high efficiency and be fabricated at low cost relative to other thin film and silicon based technologies.

Example 3

Another embodiment of a nanoparticle sensitized solar cell is shown in FIG. 8 . A suitable transparent substrate (810) is first coated with a fluorine-doped tin oxide layer (820) by methods known in the art, followed by depositing a 300 nm to 2 micron thick layer by magnetron sputtering or other thin film deposition process. Titanium film layer. By using methods known in the art, the Ti film is anodized and heat treated to obtain transparent _Ti02 nanorods (840). The conditions of anodization are optimized to obtain a barrier layer (850) that acts like an insulator and prevents shorting of the cathode/anode in the solar cell. The surface of TiO ₂ nanorods contains hydroxyl (-OH) functional groups. Nanoparticles made of luminescent materials such as CdSe, ZnSe, PbSe, InP, PbS, III-V materials with appropriate functional groups (-COOH, -NH ₂ , -H ₂ PO ₄ or -SO ₃ H) Reaction with _TiO2 nanorods to obtain nanoparticle (870) sensitized _TiO2 nanorods. Nanoparticles modify nanorods by forming monolayers through a molecular self-assembly process. Use solvent washing to remove loosely bound nanoparticles. Since the deposition of nanoparticles on TiO ₂ nanorods is controlled by the reaction of -OH functional groups on TiO ₂ with nanoparticle functional groups (-COOH, -NH ₂ , -PO ₄ , -SO ₃ H), the nanoparticles The thickness is automatically limited to a few monolayer thicknesses. A hole transport layer (880) is then deposited. The hole transport layer may be a polymeric material such as a conductive polymer, eg PEDOT. Finally electrodes (transparent or translucent) are deposited (890) to complete the cell. If a translucent electrode (890) is deposited, then the cell will be oriented so that sunlight (100) falls on the transparent substrate (810). When sunlight falls on the solar cell shown in Figure 8, electron-hole pairs are created by the nanoparticles. Due to the direct attachment of the nanoparticles to the electronically conductive _TiO2 nanorods, easy charge separation occurs thereby minimizing charge recombination.

Example 4

Another embodiment of a nanoparticle sensitized solar cell is shown in FIG. 9 . By using methods known in the art, the Ti metal foil (910) is anodized to obtain transparent _Ti02 nanorods (930). The conditions of anodization are optimized to obtain a barrier layer that acts like an insulator and prevents shorting of the cathode/anode in the solar cell (920). The surface of TiO ₂ nanorods (930) contains hydroxyl (-OH) functional groups. Nanoparticles made of luminescent materials such as CdSe, ZnSe, PbSe, InP, PbS, III-V materials with appropriate functional groups (-COOH, -NH ₂ , -H ₂ PO ₄ or -SO ₃ H) The particles were reacted with _TiO2 nanorods to obtain nanoparticle (950) sensitized _TiO2 nanorods. Nanoparticles modify nanorods by forming monolayers through a molecular self-assembly process. Wash with solvent to remove loosely bound nanoparticles. Since the deposition of nanoparticles on TiO ₂ nanorods is controlled by the reaction of -OH functional groups on TiO ₂ with nanoparticle functional groups (-COOH, -NH ₂ , -PO ₄ , -SO ₃ H), the nanoparticles The thickness is automatically limited to a few monolayer thicknesses. A hole transport layer (960) is then deposited. The hole transport layer may be a polymeric material such as a conductive polymer, eg PEDOT. Finally a transparent conductive layer (970) such as ITO is deposited to complete the cell. The solar cells are oriented such that sunlight (980) falls on the transparent conductive layer (970). When sunlight falls on the solar cell shown in Figure 9, electron-hole pairs are generated by the luminescent nanoparticles. Due to the direct attachment of the nanoparticles to the electronically conductive _TiO2 nanorods, facile charge separation occurs thereby minimizing charge recombination.

Example 5

In an alternative embodiment of the solar cell of FIG. 6, the method of Example 1 is employed, except as follows. After the TiO ₂ nanotubes are formed, nanoparticles made of Si, Ge or SiGe with appropriate functional groups are reacted with the TiO ₂ nanotubes to obtain nanoparticle (570) sensitized TiO ₂ nanotubes. As shown in Figure 6, Si, Ge or SiGe nanoparticles (570) modify the nanotubes by forming a monolayer through a molecular self-assembly process.

A hole transport layer (580) is then deposited. The hole transport layer can be p-doped Si or Ge. When using Si nanoparticles, it is desirable to use p-doped Si. The silicon layer can be amorphous silicon or polycrystalline silicon. The hole transport layer can be deposited by using methods known in the art for preparing thin films of Si or Ge. It is desirable to achieve conformal coating of nanoparticles with the hole transport layer. This can be achieved by depositing Si or Ge thin films using atomic layer deposition or chemical vapor deposition. Si and Ge thin films can be deposited on top of each other to increase the absorption of light. In such a case, the Si and Ge films function not only as a hole transport layer but also as a light absorbing layer. The hole transport layer can also be an organic semiconducting or conducting polymeric material.

Another version of this embodiment is a modification of the structures in Figures 6, 7, 8 and 9 to utilize Si, Ge or SiGe nanoparticles and/or p-doped Si and/or Ge as the hole transport layer.

Example 6

An example of a broadband solar cell with multi-sized silicon nanoparticles attached to TiO nanotubes built on fluorine _- doped tin oxide is shown in FIG. 10 . If the protocol of Example 1 is followed, a suitable transparent substrate (1010) is deposited by employing methods known in the art. However, nanoparticles of different sizes made of Si(1050), Ge(1060) or SiGe(1070) with appropriate functional groups were reacted with _TiO2 nanotubes (1040) to obtain broadband mixtures of nanoparticles sensitized TiO ₂ nanotubes. As shown in Figure 10, nanoparticles of different sizes and/or compositions (1050, 1060, and 1070) modify nanotubes by forming monolayers through a molecular self-assembly process.

Then, a hole transport layer is deposited (1080). The hole transport layer can be p-doped Si or Ge. When using Si nanoparticles, it is desirable to use p-doped Si. The silicon layer can be amorphous silicon or polycrystalline silicon. The hole transport layer can be deposited by using methods known in the art for preparing thin films of Si or Ge. Si and Ge thin films can be deposited on top of each other to increase the absorption of light. In this case, the Si and Ge films function not only as the hole transport layer but also as the light absorbing layer. The hole transport layer can also be an organic semiconducting or conducting polymeric material.

Another version of this embodiment is shown in FIG. 11 . In this case, a transparent conductive oxide (TCO) layer (1190) is deposited on top of the hole transport layer (1180) and the solar cell is oriented so that sunlight falls on the TCO. Another version of this embodiment with _Ti02 nanorods (or nanowires) on fluorine-doped tin oxide is shown in FIG. 12 . Another version of the embodiment with _TiO2 built on titanium foil is shown in Figure 13. Nanorods can be grown by methods known in the art including colloidal growth, chemical vapor deposition and MBE.

Example 7

An example of a solar cell device with layers of silicon nanoparticles of different sizes layered on TiO nanotubes built on fluorine _- doped tin oxide is shown in Figure 14. Follow the scheme of Example 1, except for the following. After the formation of the _TiO2 nanotubes (1440), nanoparticles made of Si, Ge or SiGe with appropriate functional groups are deposited on the _TiO2 nanotubes using a molecular self-assembly process to obtain multilayered nanoparticles (1450 , 1460 and 1470) sensitized TiO ₂ nanotubes. As shown in Figure 14, the nanoparticles (1450, 1460 and 1470) modify the nanotubes by forming multiple layers of nanoparticles. Each of these layers is deposited individually using a molecular self-assembly process. Each layer may contain narrow size range nanoparticles made of Si or Ge. Each layer can be designed to absorb a narrow range of the solar spectrum. Multiple layers (1450, 1460, and 1470) are stacked in such a way as to cover a desired portion (or all) of the solar spectrum. The number of layers can range from 2 to 10. It is desirable that the number of layers be minimized to reduce manufacturing costs. By adjusting the range of particle sizes used in each layer, solar cells can be designed with a preferred number of layers. The example shown in Figure 14 has three layers, layer 1 (1450) absorbing in the IR range, layer 2 (1460) absorbing in the visible range and layer 3 (1470) absorbing in the near UV range. Si and Ge nanoparticles of various sizes can be combined in this example.

Then, a hole transport layer is deposited (1480). The hole transport layer can be p-doped Si or Ge. When using Si nanoparticles, it is desirable to use p-doped Si. The silicon layer can be amorphous silicon or polycrystalline silicon. The hole transport layer can be deposited using methods known in the art for preparing Si or Ge thin films. The hole transport layer can also be an organic semiconducting or conducting polymeric material.

Other versions of this embodiment are shown in FIGS. 15 , 16 and 17 . In Figures 15 and 17, a transparent conductive oxide (TCO) layer (1590 or 1790) is deposited on top of the hole transport layer (1580 or 1780) and the solar cell is oriented so that sunlight falls on the TCO.

Another version of this embodiment with _Ti02 nanorods (or nanowires) on fluorine-doped tin oxide is shown in FIG. 16 .

Another version of the embodiment with _Ti02 nanorods (or nanowires) built on titanium foil is shown in FIG. 15 . Nanorods can be grown by methods known in the art including colloidal growth, chemical vapor deposition and MBE.

Example 8

In another embodiment, the protocol of Example 1 is modified as follows. After the formation of _TiO2 nanotubes, photosensitive nanoparticles made of groups II-V, II-VI, II-IV with appropriate functional groups react with _TiO2 nanotubes to obtain nanoparticles (590) sensitized _TiO2 nanotubes. (See Figure 6) Examples of these nanoparticles include CdSe, CdTe, ZnSe, PbSe, ZnS, PbS. As shown in Figure 6, nanoparticles modify nanotubes by forming monolayers by a molecular self-assembly process.

A hole transport layer (580) is then deposited. The hole transport layer may be a p-doped semiconductor layer such as Si or Ge. The Si or Ge layer can be amorphous or polycrystalline. The hole transport layer may also be a metal oxide layer such as aluminum oxide, nickel oxide, or the like. The hole transport layer can be deposited by employing methods known in the art for depositing thin films of these materials. For example, Si or Ge thin films can be deposited by atomic layer deposition or chemical vapor deposition. Si and Ge thin films can be deposited on top of each other to increase the absorption of light. In this case, the Si and Ge films function not only as the hole transport layer but also as the light absorbing layer. The thickness of the hole transport layer can be adjusted to minimize the resistance of hole conduction through this layer and to maximize the absorption of light. The hole transport layer can also be an organic semiconducting or conducting polymeric material.

Another version of the embodiment with _TiO2 nanotubes built on titanium foil is shown in Figure 7. In this case, a transparent conductive oxide (TCO) layer (770) is deposited on top of the hole transport layer (760) and the solar cell is oriented so that sunlight falls on the TCO. Another version of the embodiment with _Ti02 nanorods (or nanowires) on fluorine-doped tin oxide is shown in FIG. 8 . Another version of the embodiment with _Ti02 nanorods (or nanowires) built on titanium foil is shown in FIG. 9 . Nanorods can be grown by methods known in the art including colloidal growth, chemical vapor deposition and molecular beam epitaxy (MBE).

Example 9

In another embodiment, the protocol of Example 8 was modified as follows. The hole transport layer is made of a p-doped semiconductor layer such as Si or Ge instead of the hole transport layer of Si or Ge.

Other versions of this embodiment are shown in FIGS. 11 , 12 and 13 .

Example 10

In another embodiment, the broadband solar cell described in Example 6 is modified as follows. After the formation of TiO ₂ nanotubes (1440) (see Figure 14), photosensitive nanoparticles of different sizes made of II-V, II-VI and II-IV groups, etc., with suitable functional groups were combined with TiO ₂ nanotubes The tubes were reacted to give _TiO2 nanotubes sensitized by a broadband mixture of nanoparticles (1450, 1460 and 1470). Examples of photosensitive nanoparticles include CdSe, ZnSe, PbSe, CdTe, PbS, and the like. The size of the nanoparticles may vary in the range 2-50 nm, preferably from 2-10 nm. Photosensitive nanoparticles with appropriate functional groups were deposited on _TiO2 nanotubes using a molecular self-assembly process to obtain multilayer nanoparticle-sensitized _TiO2 nanotubes. Each of these layers can be deposited individually by employing a molecular self-assembly process. Each layer can contain photosensitive nanoparticles of a narrow size range and can be designed to absorb a narrow range of the solar spectrum. Multiple layers (1450, 1460, and 1470) are stacked in such a way as to cover a desired portion (or all) of the solar spectrum. The number of layers can range from 2 to 10. A minimum number of layers is desired to reduce manufacturing costs. By adjusting the size range of particles used in each layer, solar cells can be designed with a preferred number of layers. In Figure 14, layer 1 (1450) absorbs in the IR range, layer 2 (1460) absorbs in the visible range, and layer 3 (1470) absorbs in the near ultraviolet range. Nanoparticles of PbSe, CdSe and ZnSe of various sizes can be combined to construct the multilayer structure shown in FIG. 14 .

A hole transport layer (1480) is then deposited. The hole transport layer may be a p-doped semiconductor layer such as Si or Ge. This layer can be amorphous or polycrystalline. Si and Ge thin films can be deposited on top of each other to increase the absorption of light. The Si and Ge films function not only as a hole-transporting layer but also as a light-absorbing layer. The thickness of the hole transport layer can be adjusted to minimize the resistance of hole transport through this layer while maximizing light absorption. The hole transport layer can also be an organic semiconducting or conducting polymeric material.

Other versions of this embodiment are shown in FIGS. 15 , 16 and 17 .

Claims (30)

1. photovoltaic device, it comprises:

First electrode and second electrode, at least one is transparent to solar radiation in described two electrodes;

Ground floor, it comprises electron conduction nanostructure and logical with described first electrode conductance;

Photoactive layer, it comprises photosensitive nanoparticles and contiguous described electron conduction nanostructure; And

Hole transmission layer, it contacts described photoactive layer and described second electrode.

2. photovoltaic device as claimed in claim 1 also is included in the barrier layer between described hole transmission layer and described first electrode.

3. photovoltaic device as claimed in claim 1, wherein said electron conduction nanostructure comprises nanotube, nanometer rods or nano wire.

4. photovoltaic device as claimed in claim 3, wherein said nanostructure comprises nanotube.

5. photovoltaic device as claimed in claim 4, wherein said nanotube comprises titanium dioxide.

6. photovoltaic device as claimed in claim 1, wherein said photosensitive nanoparticles comprise quantum dot, nanometer rods, nanometer bipod, nanometer tribrach, nanometer multiway platform or nano wire.

7. photovoltaic device as claimed in claim 6, wherein said photosensitive nanoparticles is a quantum dot.

8. photovoltaic device as claimed in claim 1, wherein said photosensitive nanoparticles is covalently attached to described nanostructure.

9. photovoltaic device as claimed in claim 1, wherein said photosensitive nanoparticles comprise CdSe, ZnSe, PbSe, InP, PbS, ZnS, Si, Ge, SiGe, CdTe, CdHgTe or II-VI, II-IV or III-V family material.

10. photovoltaic device as claimed in claim 1, wherein said photoactive layer comprise first nano particle and second nano particle of absorption from the radiation of solar spectrum different piece.

11. photovoltaic device as claimed in claim 10, wherein said first nano particle is different on component with second nano particle.

12. photovoltaic device as claimed in claim 10, wherein said first nano particle and second nano particle are of different sizes.

13. photovoltaic device as claimed in claim 10, wherein said first nano particle and second nano particle are different on size and component.

14. photovoltaic device as claimed in claim 1 also comprises second photoactive layer, the wherein said ground floor and the described second layer absorb the radiation from the different piece of solar spectrum.

15. photovoltaic device as claimed in claim 14, the described nano particle of wherein said first photoactive layer and described second photoactive layer is different on component.

16. photovoltaic device as claimed in claim 14, the described nano particle of wherein said first photoactive layer and described second photoactive layer is of different sizes.

17. photovoltaic device as claimed in claim 14, the described nano particle of wherein said first photoactive layer and described second photoactive layer is different on size and component.

18. photovoltaic device as claimed in claim 1, wherein said hole transmission layer comprises hole transport polymer.

19. photovoltaic device as claimed in claim 18, wherein said hole transport polymer comprise p N-type semiconductor N polymer.

20. photovoltaic device as claimed in claim 19, wherein said p N-type semiconductor N polymer comprises P3HT, P3OT, MEH-PPV or PEDOT.

21. photovoltaic device as claimed in claim 20, wherein said polymer comprises PEDOT.

22. photovoltaic device as claimed in claim 1, wherein said hole transmission layer comprises the p N-type semiconductor N.

The SiGe that Ge that Si, p that 23. photovoltaic device as claimed in claim 22, wherein said p N-type semiconductor N are p to mix mix or p mix.

24. photovoltaic device as claimed in claim 22, wherein said p N-type semiconductor N comprise the microcrystal silicon of p doped amorphous silicon, p doping or the nanocrystal silicon that p mixes.

25. photovoltaic device as claimed in claim 1, wherein said hole transmission layer comprise the p N-type semiconductor N of two-layer or multilayer.

26. photovoltaic device as claimed in claim 25, wherein said p type semiconductor layer comprise silicon layer, the germanium layer of p doping or the SiGe layer that p mixes that p mixes.

27. a method that is used to make photovoltaic device comprises:

Form the ground floor that comprises the electron conduction nanostructure on first electrode, wherein said ground floor and described first electrode conductance are logical;

On described electron conduction nanostructure, form the photoactive layer that comprises photosensitive nanoparticles; With

On described photoactive layer, form hole transmission layer; And

On described hole transmission layer, form described second electrode;

In wherein said first electrode and described second electrode at least one is transparent to solar radiation.

28. method as claimed in claim 27 forms the barrier layer before also being included in the described nanostructure of formation or forming described hole transmission layer.

29. method as claimed in claim 27, the described formation of wherein said photoactive layer comprise the photoactive layer that uses different nano particles to comprise the random distribution of described different nano particle with manufacturing.

30. method as claimed in claim 27, the described method that wherein said photoactive layer comprises two-layer at least different nano particle and forms described photoactive layer is included in layer that forms first nano particle on the described nanostructure and the layer that forms second nano particle on the layer of described first nano particle, and wherein said first nano particle is different with second nano particle.

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