Photovoltaic cell for laser beam power detection

Abstract

A wireless optical power transmission system comprises a transmitter and a receiver, the transmitter comprising a laser emitting a light beam, a scanning mirror for directing the light beam towards the receiver, and a control unit receiving signals from a detection unit on the receiver and controlling the light beam power and the scanning mirror. The receiver has a photovoltaic cell with a bandgap energy of 0.75-1.2 eV, having a plurality of conductors on the light beam receiving surface. A cover layer of a material blocking illumination having a wavelength outside the wavelength of the laser is provided on the photovoltaic cell. The cover layer can have an anti-reflective coating on its top surface and bottom surface. The detection unit thus generates a signal representing the power of the laser beam impinging on the receiver independent of illumination other than the light beam. The control unit can thus maintain the laser power impinging on the receiver.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic cells, and more particularly to photovoltaic cells suitable for converting a beam of light from a laser power source into electrical energy in a wireless power system. Background Technology

[0002] Photovoltaic cells (also known as PV cells) are designed and used in many systems to convert light (visible or invisible) into electrical energy. In wireless power systems, photovoltaic cells are used to convert laser light directed from a transmitter to the cell into usable electricity. In such systems, accurately measuring the amount of laser light received by the cell is important for many reasons, such as maintaining proper beam aiming, ensuring safe operation of the system, and efficiently converting the power generated by the photovoltaic cells into usable, stable electrical power.

[0003] In a typical photovoltaic cell, one or more pn junctions are used to convert light into electrical energy, and two electrodes are used to extract the electrical energy from the cell. The bottom electrode is typically metal-coated, while there are usually two options for the top electrode:

[0004] (i) A metal grid, typically made of aluminum, silver or gold, has low series resistance but reflects the portion of the light that falls on the grid itself and prevents it from entering the battery.

[0005] (ii) A continuous, nearly transparent conductive coating (e.g., indium tin oxide (ITO)) that allows most of the light to pass through into the cell, but has a higher resistance than a metal grid structure, resulting in higher ohmic loss.

[0006] In the case of a metallic grating, a trade-off typically exists between ohmic loss and optical loss due to reflection from the metallic grating. Ohmic loss is determined by V... 2 The / R measurement shows that V is the battery voltage and R is the series resistance. Ohmic losses decrease with increasing metal coverage of the battery, while optical losses, known as the "shading effect," increase with increasing metal coverage. An optimal balance typically exists between these two factors, which typically depends on the desired battery illumination and the current of the PV cell.

[0007] In the article “GaSb-Based Solar Cells for Full Solar Spectrum Energy Harvesting” published by Lumb et al. in Adv. Energy Mater. 2017, 1700345 (2017), it is claimed that a PV cell with an efficiency of 44.5% in converting sunlight into electricity has been developed.

[0008] According to Green et al. (Prog. Photovolt:Res.Appl.2017;25:3-13, published online on November 28, 2016 in Wiley Online Library (wileyonlinelibrary.com).DOI:10.1002 / pip.2855), the highest reported photovoltaic efficiency is 46%, as demonstrated by TND Tibbits et al. at the 29th International Photovoltaic Conference held in Amsterdam, Netherlands in September 2014. th This was published in an article titled "Comparison of direct growth and wafer bonding for the fabrication of GaInP / GaAs dual-junction solar cells on silicon" at the PV Solar Energy Conference and Exhibition.

[0009] In the paper "Reduction of front-metallization grid shading in concentrator cells through laser micro-grooved cover glass" published by Garcia-Linares in AIP Conference Proceedings 1679,060001(2016); doi:10.1063 / 1.4931535, a composite glass "microlens" was proposed, designed to focus light away from the conductor grid, thereby minimizing grid loss. This composite microlens pattern requires precise placement relative to the metal grid and has not been widely adopted.

[0010] Unless such composite “microlens” optics are used, there is a normal trade-off between ohmic loss and shielding loss, and the typical result is optical loss in the range of 2-10%, with similar ohmic loss for high-concentration photovoltaic cells.

[0011] In a review entitled “Optics for concentrating photovoltaics: Trends, limits and opportunities for materials and design” published by K. Shanks et al. in Renewable and Sustainable Energy Reviews, 60 (2016), pp. 394-407 (2016), the available PV optics are covered, and it is noted that if the trade-off between conductor ratio and optical shading is eliminated without using complex optics that require precise placement of metal grids, the cell efficiency in photovoltaic cells could potentially be improved by 3-20%.

[0012] In his article "Shading losses of solar-cell metal grids," published in the Journal of Applied Physics, Vol 71, 5237 (1992), A.W. Blakers described a system for minimizing shading losses. He proposed using a circular, finger-shaped conductor instead of the typically flat, rectangular conductor, as the finger shape would guide more of any incident light reflected from the PV element surface back to the PV element surface for absorption.

[0013] PV designers use grid optimization to optimize the conductors of existing PV cells. An example of such a grid calculator can be seen at https: / / www2.pvlighthouse.com.au / calculators / Grid%20calculator / Grid%20calculator.aspx. When using this grid calculator, users can choose between different shapes of the conductive fingers (rectangular, triangular, elliptical, pseudo-rectangular) and different materials, widths, and heights. However, users cannot select any optical overlays for the cell, nor can they optimize such coatings. Optimizing the grid using this tool allows for comparison of different trade-offs between different cell metal overlays. The same site defines shading loss as "shading loss caused by the presence of metal on the top surface of a solar cell, which prevents light from entering the solar cell." Shading loss is determined by the transparency of the top surface; for a planar top surface, transparency is defined as the portion of the top surface covered by metal. Transparency is determined by the width and spacing of the metal lines on the surface. An important practical limitation is the minimum linewidth associated with a specific metallization technology. For the same transparency, narrow linewidth technology allows for closer finger spacing, thereby reducing transmitter resistive losses.

[0014] Current conventional methods for optimizing conductor grids can also be found in Stuart R. Wenham et al.'s "Applied Photovoltaics" (3rd edition, copyrighted 2012). On page 62 of the online reference, it states that "the optimal width (Wb) of the bus will emerge when the resistive loss in the bus equals its shading loss," and illustrates various methods known in the art for mitigating this loss. While different options for increasing light capture in the cell are discussed, options for recovering reflected light are not mentioned.

[0015] However, while the PV cells described in these references offer high efficiency, they are typically optimized to achieve maximum efficiency when converting solar energy into electrical energy, which may have different technical requirements than converting the power of a laser beam into electrical energy.

[0016] Therefore, there is a need for a photovoltaic cell for converting wirelessly transmitted laser beams into electrical power that overcomes at least some of the shortcomings of existing technology systems and methods.

[0017] The disclosure of each of the publications mentioned in this and other parts of the specification is incorporated herein by reference in its entirety. Summary of the Invention

[0018] This disclosure describes a novel exemplary system for use within a wireless laser power transmission system, comprising a PV cell with a covering layer for converting the power of a laser beam into electrical energy. The configuration described in this disclosure aims to improve photovoltaic efficiency and enhance the security and accuracy of power measurements performed using these PV cells by simultaneously achieving several objectives:

[0019] a) Reduce the dependency between the coverage area of ​​the metal fingers and the occlusion (shadow).

[0020] b) Reduce the amount of light reflected from the battery.

[0021] c) Recover the reflected light into electrical energy.

[0022] d) Reduce ohmic losses in the series resistance of conductors.

[0023] e) Improve the accuracy of laser power measurement using photovoltaic cells when irradiated from different angles.

[0024] f) Improve the accuracy of laser power measurement using photovoltaic cells when used under different lighting conditions (e.g., outside, inside, or near a heat source).

[0025] g) Confirm that the power of the directional laser emission reaches its intended receiver and is at the intended power level, i.e., no unreasonable power level is “lost” along the way.

[0026] In many cases, the beam aiming mechanism and / or safety mechanism of a wireless laser power transmission system depends on the accurate measurement of the laser power received by the photovoltaic cell. For example, if the laser aiming is adjusted until the maximum power from the PV is generated, accurate aiming can be affected by sunlight, which can cause measurement deviations over time, for example, if the cell is illuminated for one instant and not for the next. In systems where safety depends on power measurement, illumination from different directions should optimally yield similar power measurement results, and sunlight or heat sources should never cause deviations in the measurement results beyond small safety limits. The device disclosed herein allows measurements to be substantially independent of the direction of illumination and other light sources with different wavelengths that can illuminate the system.

[0027] If light reflected from both the front surface and the conductor of the photovoltaic cell is collected and directed to the area of ​​the cell not covered by the metal grid, it is possible to increase the coverage of the metal grid and thus reduce ohmic losses, while also reducing shading effects and allowing for accurate optical power estimation based on the generated electrical power in a manner independent of beam direction and even beam uniformity. In the case of narrow conductors (as in prior art cells), if the beam only illuminates a portion of the cell, the narrow conductor will produce greater ohmic losses than with uniform illumination, and therefore optical power estimation based on electrical power or current will be inaccurate. On the other hand, the configuration currently described allows for lower ohmic losses and therefore more accurate optical power estimation based on electrical power measurements.

[0028] However, light is applied to the photovoltaic cell from different directions and reflected by the grid in complex patterns, which can include several orders of Bragg reflection, typically caused by the periodic structure of the grid. This effect presents several problems. First, reflected light is lost, reducing efficiency. Second, reflected light can pose a safety hazard. Third, because the amount of reflected light depends on the direction of illumination, optical power measurements taken from the photovoltaic cell will be inaccurate and become less useful for safety and aiming purposes. In many cases, the system's safety mechanisms depend on accurate measurement of the laser power received by the photovoltaic cell.

[0029] In typical wireless power systems, there is no PV reorientation when the beam direction changes; that is, the PV does not automatically tilt to maximize power. The laser can illuminate the battery from almost any direction. Typically, such a system can operate at a maximum of 60 degrees from the normal to the battery surface. Therefore, light reflected from the conductor will be reflected at different angles, ranging from approximately ±70 degrees or even greater from the battery normal, where the primary reflection is opposite to the angle of the incoming beam. If a symmetrical field of view is to be maintained, allowing the beam to originate from either side of the PV, then any collection system located within that field of view must be transparent, including any supporting structures for the optical elements, otherwise it would impede the battery's ability to collect light from these directions.

[0030] An efficient collection system must also cover a significant portion of the field of view in all directions to be efficient. This means that if a beam is incident from one direction and generates a reflected beam in another, in order for the collection system to intercept and collect the reflected beam in that other direction, it is unavoidable to block the incident light coming from that other direction, since the collection system is opaque. In other words, in terms of the served field of view, any angle of incidence within the field of view will produce a reflection in some direction. To recover light traveling (or reflected) along that direction, an opaque collection system must be placed in the direction of reflection, thereby efficiently eliminating that direction from the field of view.

[0031] One object of the present invention is to introduce a system that will improve the efficiency, aiming accuracy and safety of such systems.

[0032] In one exemplary implementation, the shape of the conductors on the PV is chosen such that they reflect light in a wide pattern. Typical structures depend primarily on manufacturing capabilities and the desired field of view of the incoming light, i.e., the angle from which the light might originate, but as a general concept, common planar square or rectangular conductor grids are not preferred, while circular and triangular grids are more advantageous.

[0033] Current systems can use PVs with conductors that are optimally shaped to prevent shading losses. The shape of the conductors on the PV can be chosen such that they reflect light in a broad pattern. For example, the conductors can be circular and finger-shaped, or triangular. This can result in reflections from the conductors being directed onto the absorbing PV cell, or undergoing total internal reflection by a coating layer on the cell, thereby improving system efficiency. This also prevents hazardous reflections from the PV cell (e.g., potentially causing eye damage) because light reflected from the conductors is diffused and therefore not reflected uniformly.

[0034] The PV configuration disclosed herein differs significantly from prior art PVs in that the cover layer can be coated with an anti-reflective (AR) coating on both of its interface surfaces, namely, an external AR coating between the cover layer and the outside air, and an internal AR coating between the cover layer and the light-absorbing surface of the PV cell material.

[0035] External anti-reflective (AR) coatings are designed to transmit essentially only the wavelengths of the laser beam (typically infrared) and reflect all other wavelengths that may be present in external irradiation and affect the PV cell's ability to measure the laser wavelength. Therefore, AR coatings do not need to reflect any wavelengths to which the PV cell is insensitive (e.g., those in the mid-infrared and far-infrared, or wavelengths in the UV), as these will not affect measurements at the laser wavelength.

[0036] Additionally, the capping layer should include a material that absorbs wavelengths other than the wavelength of the laser beam, such that any wavelengths not reflected by the AR coating are absorbed by the capping layer and therefore do not reach the pn junction(s) of the PV cell, thus preventing inaccurate laser power transmission readings. Therefore, the upper layer of the PV cell should absorb visible wavelengths that might not be reflected by the AR coating and thus could reach the upper layer of the semiconductor PV cell material itself, just like the capping layer itself. This is achieved by selecting an upper layer of PV cell material with a sufficiently low bandgap.

[0037] One purpose of blocking wavelengths other than the laser beam's wavelength from reaching the pn junction of the PV absorber is to ensure that, when used as a safe power timer for the transmitter, the receiver provides an accurate reading of the amount of laser beam striking it. Therefore, other incident irradiation should not interfere with this measurement, and thus should be blocked before other incident irradiation impacts the PV absorber.

[0038] Furthermore, the capping layer should have a high refractive index to lower the critical angle of total internal reflection (TIR), thereby capturing as much of the laser beam that enters it and is reflected from the surface and conductor as possible. This effect will be explained in more detail below. This is to maximize the amount of irradiation reaching the absorptive PV cell, since a portion of the beam reflected from the conductor may be re-reflected from the capping layer, and thus prevents escape from the PV cell, which would occur without the capping layer.

[0039] This also has the following advantages: any light leaving the PV cell after multiple reflections inside the capping layer, on the PV cell surface, between conductors, and after total internal reflection from the top of the capping layer will be in different "random" directions and positions. This is in contrast to some existing PV configurations that reflect the beam in a more uniform manner.

[0040] The top of the PV layer (i.e., the bottom of the cover layer) can also be coated with an AR coating, which will maximize the absorption of any light that will strike the cover layer into the PV cell material.

[0041] According to another implementation, and taking advantage of the benefits provided by the dual anti-reflective coating, a wireless optical power transmission system is described, comprising a transmitter, a receiver, and a control unit, wherein:

[0042] a) The transmitter includes: a laser suitable for emitting a beam; and a scanning mirror suitable for guiding the beam toward a receiver, and

[0043] b) The receiver includes: a photovoltaic cell having at least one junction with a bandgap energy between 0.75 eV and 1.2 eV; and a detection unit adapted to detect the power of a laser beam striking the receiver by illumination at wavelengths outside the wavelength range of the laser beam; and

[0044] c) The control unit is adapted to receive signals from the detection unit and interact with at least one of the following: (i) the power of the beam emitted by the laser; and (ii) the position of the scanning mirror.

[0045] The detection unit then generates a signal representing the power of the laser beam striking the receiver, which is advantageously independent of illumination by wavelengths outside the wavelength of the laser beam.

[0046] The control unit can then use this signal to operate in two functionally different ways. In one implementation, the control unit uses the signal to control at least one of the following: (i) the power of the beam; and (ii) the position of the “scanning” mirrors, such that they are adjusted to provide optimal aiming output to the receiver. This is the conventional role of the control system, which operates to actively control or “tune” the system to provide optimal power input at the system’s ultimate target (i.e., the receiver).

[0047] The term “scanning mirror” is used herein to refer to any movable mirror, which is intended to include either a mirror that is fixed in place or slowly moved to aim a charging beam at a receiver and keep it aimed at the receiver rather than scanning the surrounding environment. This is an alternative description of “scanning” mirrors with different functions.

[0048] According to the second configuration, the control system can also operate as a safety verification system to ensure that the laser power beam does not deflect into an unintended direction that could cause damage. This system provides a warning when a laser beam is expected to guide a beam with a specific power to the receiver, but the receiver does not receive all or any of that power, indicating that at least a portion of the beam power is deflecting into an unintended direction. This is achieved by using a control system whose role is the opposite of its usual operation—that of a system verification system rather than a control system. In this mode, the control system receives data related to the output power from the laser input and data related to the beam's aiming direction from the scanning mirror input, the output power being either indicated by the laser or by measurements at the transmitter. These data can then be combined in the controller and compared with a signal generated in the detector unit related to the actual laser power received there. Any deviation between the expected laser power from these two sets of data that exceeds a predetermined error or loss margin can be used to trigger a safety warning state regarding erratic beam transmission or the presence of an obstacle in the beam path causing the expected beam to decrease or deflect.

[0049] Cover layer

[0050] A capping layer can be advantageously applied to a conductor, the capping layer having a high refractive index, typically above 1.5, preferably above 1.6 or 1.65, or even a semiconductor coating having a refractive index above 2 but certainly above 1.3.

[0051] In one implementation, the capping layer consists of a polymer layer or a dielectric layer covered by a glass layer. The capping layer is an optical layer that can have a uniform structure, but typically has a top volume and a bottom volume, and can consist of many different transparent or translucent layers and have the following properties.

[0052] The top volume of the optical cladding layer is in contact with the surrounding environment (typically air) but may also be in contact with other materials. The top volume is typically a hard glass layer, which is more protective than the softer inner volume of the cladding layer. Additionally, the top volume can be chosen to have a higher refractive index than the main volume to increase the likelihood of internal light undergoing total internal reflection. The bottom of the optical cladding layer is in contact with both the surface of the PV (typically including an AR coating) and the conductors described above. The cladding layer should be as transparent as possible to the wavelength of the incoming light beam, thus requiring an optical density of less than 2 for the beam wavelength, preferably less than 1, or even 0.5. Some materials may even allow optical densities less than 0.1 or even less than 0.01; however, simultaneously, the cladding layer should be configured to block, absorb, or reflect most wavelengths other than the wavelength of the light beam to prevent other wavelengths that may come from sunlight or other irradiation sources from reaching the pn junction(s). Therefore, the optical density should have a value of 0.5 for these wavelengths. The top of the PV is typically coated with an AR coating, which in prior art PVs is typically adapted to minimize reflections between air (refractive index approximately 1) and the PV (typically refractive indices 2-4).

[0053] In the case of the battery disclosed herein, the bottom AR coating should be designed to minimize reflection of the laser wavelength between the PV (refractive index 2-4) and the optical cover layer (refractive index 1.5-2) for the wavelength of the light beam, while reflecting both shorter and longer wavelengths from the battery. Two AR coatings can be used to suppress unwanted wavelengths. An AR coating can be applied to the top of the cover layer, which is adapted to minimize reflection of the light beam between the air (refractive index approximately 1) and the top of the cover layer, while increasing reflection of other wavelengths.

[0054] The cladding layer “shields” the PN junction from light that is not part of the laser beam itself, which is crucial for safety and accuracy of aiming measurements. This can be achieved either by absorbing this unwanted light or by reflecting it away from the PV cell. As described above, the AR coating of the cladding layer reflects external illumination outside the laser band, and the cladding layer further absorbs any light that is not reflected. In many cases, the PN junction will be inefficient for very long wavelengths, thus eliminating the need to block such wavelengths.

[0055] The overall structure of the grid itself

[0056] The density of the grid lines should be selected based on various parameters, as explained below.

[0057] It is advantageous if the spacing between the grid lines is greater than the operating wavelength divided by 2 * the refractive index of the capping layer.

[0058]

[0059] Where d is the spacing between the wires, λ is the operating wavelength in vacuum, and n is the refractive index of the coating layer.

[0060] It is also advantageous for d < 100λ if the spacing between the grid lines is less than 100 times the operating wavelength in vacuum.

[0061] It is also preferable if the optical coating is selected such that it has minimal absorption of the operating wavelength but does absorb shorter wavelengths.

[0062] If the conductor is coated with a diffusion coating, the above size restrictions can be lifted.

[0063] Physical explanation

[0064] When light is reflected from the grid of a conventional photovoltaic cell, it is typically irrecoverable because it is reflected at an unknown angle, and it is difficult, if not impossible, to construct a light-collecting system that does not obstruct the incident beam. Furthermore, when a conventional photovoltaic cell is placed under direct sunlight, it will achieve a light collection efficiency of 100 mW / cm². 2 The sunlight is converted into electrical power, which makes the laser power reading inaccurate, potentially affecting safety and aiming.

[0065] The photovoltaic cell disclosed herein utilizes four separate design features to overcome many of the drawbacks of existing PV cells described above.

[0066] 1. Due to the high refractive index of the coating used, the incoming light beam hits the conductor in a reduced field of view. According to Snell's law, the beam angle is reduced by sin(θ1) = n1 / n2*sin(θ2), so it is possible to manipulate the light reflected at an angle greater than the maximum field of view inside the coating, and this light is reflected back to the cell without obstructing the field of view.

[0067] 2. A grid structure is used to increase the amount of light reflected outside the field of view of an incoming beam through its dense grid lines and the structure of each conductor.

[0068] 3. The capping layer serves as a collection and reflection system because most of the light beam undergoes total internal reflection through the capping layer and is reflected back to the photovoltaic cell.

[0069] 4. Sunlight will be absorbed / reflected by the cover layer and its associated AR coating, so it will not affect power measurements.

[0070] The use of the overlay and the features described above allows for a reduction in optical losses of the laser beam. The device can be further improved because the ability to recover some of the light allows for an increase in the conductor's coverage area and thus a reduction in ohmic losses, and allows for an increase in the cell's fill factor, as well as the maximum power point voltage and current.

[0071] To promote efficient reflection towards the photovoltaic cells, the thickness of the capping layer should be less than the width of the photovoltaic cells. If the capping layer is thicker, light will escape from the sides of the capping layer.

[0072] All of the above design features allow for the construction of grids with more “masking” compared to normal masking as described in the prior art.

[0073] The shape of the individual conductor lines should be chosen to maximize higher-order reflections from the grid, typically as explained above.

[0074] The top volume should have an AR coating for air or desired surrounding materials (e.g., water or vacuum).

[0075] Advantages of using infrared laser to irradiate batteries

[0076] The features described herein are particularly useful for photovoltaic cells designed to convert infrared lasers into electrical energy, as such cells offer several advantages.

[0077] First, these cells are typically exposed to 10 to 100 times more power per unit area compared to the typical saturation conditions under which conventional solar cells are exposed. The current design also features a larger field of view compared to CPV cells and intentionally reduces efficiency for sunlight.

[0078] Second, infrared lasers specify lower-energy photons, which requires a lower bandgap in the pn junction. This results in lower voltage and higher current compared to conventional solar spectrum-optimized cells. Due to the higher current, ohmic losses are more significant.

[0079] By selecting materials with sufficiently low band gaps to tune the pn junction in this battery, long-wavelength photons longer than the wavelength of the laser beam are “ignored,” so that if the receiver is placed near a heat source (e.g., a heating element or an incandescent lamp), output parameters such as power, current, and voltage will be less affected by long-wavelength infrared photons.

[0080] Third, unlike typical solar radiation, which has a uniform area across a cell, laser radiation tends to form a focal point and is not "fully filled" into the cell. In many cases, the laser beam typically has an approximately circular, elliptical, or rectangular shape with a Gaussian or higher-order Gaussian attenuated power distribution. This non-uniform power distribution makes optimizing the conductor thickness more complex, and centering the power distribution around the PV using a scanning mirror typically means that electrons generated at the cell center (where most of the optical power is concentrated) produce a higher current, thus requiring a thicker conductor and therefore a lower resistance compared to the conductor required to absorb photons near the cell edges (where less optical power is present).

[0081] Fourth, specular reflections from the cell of a high-power laser could pose safety concerns and require blocking or diffusing. In any case, reflections from the cell of this disclosure have lower power, thus significantly reducing safety issues.

[0082] Advantages when using a wireless power beam transmission system to irradiate the battery

[0083] Current batteries offer numerous advantages when used as components in wireless power systems. Typically, such systems can power portable electronic devices equipped with rechargeable batteries ranging from 1 to 100 watt-hours. The required charging power is typically on the order of 0.5 to 10 W, necessitating the use of a charging beam of 1 to 30 W.

[0084] The typical beam diameter is a few millimeters, and smaller beams are difficult to keep focused within a range of 1-10 meters. Therefore, 2-10% non-diffuse reflection of the beam poses a significant risk (20mW-1W). Thus, it is essential to reduce the total amount of light reflected by the conductor while simultaneously diffusing it. Reducing reflection from the battery is also important; current batteries typically provide up to 1% reflection, instead of the usual 2-10%.

[0085] Therefore, based on an exemplary implementation of the device described in this disclosure, a power conversion device for converting optical power into electrical power is provided, the power conversion device being adapted for optical wireless power transmission using a laser beam, the power conversion device comprising:

[0086] (i) A photovoltaic cell having multiple conductors on a surface suitable for receiving a laser beam, the photovoltaic cell having at least one junction having a bandgap energy between 0.75 eV and 1.2 eV, and

[0087] (ii) A cover layer disposed on a photovoltaic cell, the cover layer comprising a material adapted to limit the transmission of irradiation by absorption or reflection, and transmitting a laser beam toward the photovoltaic cell, the irradiation having a wavelength outside the wavelength range of the laser beam.

[0088] in:

[0089] The wavelength of the laser beam is between 700nm and 1500nm.

[0090] Irradiation outside the wavelength range of the laser beam is within the range of 550nm to 700nm, and

[0091] The transmittance of the coating layer to the wavelength of the laser beam is at least 50% higher than that of the coating layer to wavelengths in the range of 550 nm to 700 nm, such that the efficiency of the power conversion device in converting the laser beam to electrical power at the wavelength is at least 2.5 times higher than that of the power conversion device at the wavelength of 550 nm.

[0092] In such a power conversion device, the bandgap energy can be tuned to the wavelength of the laser, such that for any wavelength at least 25% longer than the laser wavelength, the efficiency of optical power to electrical power conversion is less than one-quarter of the conversion efficiency at the laser wavelength. In any of the devices described above, the cladding layer may further include at least one of the following:

[0093] (i) A first anti-reflective coating disposed on the surface of a cover layer remote from the photovoltaic cell, the first anti-reflective coating being adapted to reflect irradiation and allow a laser beam to penetrate into the cover layer, the irradiation having a wavelength outside the wavelength range of the laser beam, or

[0094] (ii) A second anti-reflective coating disposed between the surface of the photovoltaic cell and the cover layer, the second anti-reflective coating being adapted to reflect irradiation and to allow a laser beam to be transmitted into the photovoltaic cell, the irradiation having a wavelength outside the wavelength range of the laser beam.

[0095] Another implementation described in this disclosure is a security system for a wireless optical power transmission system, comprising a transmitter, a receiver, and a control unit, wherein:

[0096] (i) The transmitter includes:

[0097] Lasers suitable for emitting beams, and

[0098] A scanning mirror suitable for guiding a light beam toward a receiver.

[0099] (ii) The receiver includes:

[0100] A photovoltaic cell having multiple conductors on a surface suitable for receiving a laser beam, the photovoltaic cell having at least one junction with a bandgap energy between 0.75 eV and 1.2 eV, and

[0101] A cover layer disposed on a photovoltaic cell comprises a material adapted to limit irradiation by absorption or reflection, and to transmit a laser beam toward the photovoltaic cell, the irradiation having a wavelength outside the wavelength range of the laser beam.

[0102] (iii) The control unit is adapted to receive first data indicating the position of the scanning mirror and second data indicating the power of the beam emitted by the laser from the transmitter, and to determine the desired power incident on the photovoltaic cell based on the first data and the second data, and to compare the desired power with the power of the laser beam hitting the receiver as measured by the photovoltaic cell, and to indicate a potential safety problem if the desired power deviates from the measured power by more than a predetermined level.

[0103] According to another embodiment of this application, a wireless optical power transmission system is provided, including a transmitter and a receiver.

[0104] The transmitter includes:

[0105] Lasers suitable for emitting beams

[0106] A scanning mirror suitable for guiding a light beam toward a receiver, and

[0107] A control unit adapted to receive signals from a detection unit on a receiver and to control at least one of the following: (i) the power of the beam emitted by the laser; and (ii) the position of the scanning mirror; and

[0108] The receiver includes:

[0109] A photovoltaic cell having multiple conductors on a surface suitable for receiving a laser beam, the photovoltaic cell having at least one junction with a bandgap energy between 0.75 eV and 1.2 eV, the photovoltaic cell being adapted to detect the power of a laser beam arriving at the photovoltaic cell, wherein:

[0110] The receiver includes a cover layer disposed on a photovoltaic cell, the cover layer comprising: a material adapted to absorb or reflect irradiation and transmit a laser beam toward the photovoltaic cell, the irradiation having a wavelength outside the wavelength range of the laser beam; and at least one of the following:

[0111] (i) A first anti-reflective coating disposed on the surface of a cover layer remote from the photovoltaic cell, the first anti-reflective coating being adapted to reflect irradiation and allow a laser beam to penetrate into the cover layer, the irradiation having a wavelength outside the wavelength range of the laser beam, and

[0112] (ii) A second anti-reflective coating disposed between the surface of the photovoltaic cell and the cover layer.

[0113] The second anti-reflective coating is suitable for reflecting irradiation and allows the laser beam to penetrate into the photovoltaic cell.

[0114] The irradiation has a wavelength outside the range of the laser beam's wavelength.

[0115] The detection unit generates a signal representing the power of the laser beam striking the receiver independently of irradiation with wavelengths other than the wavelength of the laser beam, and the control unit is adapted to control at least one of (i) the position of the beam and (ii) the position of the scanning mirror in order to maintain the power striking the receiver.

[0116] This disclosure describes yet another power conversion device for converting optical power into electrical power, the power conversion device being adapted for optical wireless power transmission using a laser beam, the power conversion device comprising:

[0117] A power conversion device having at least one junction having a bandgap energy between 0.75 eV and 1.2 eV, and having an outer layer through which laser light is transmitted toward the at least one junction, the outer layer being configured to transmit at least a first wavelength into the at least one junction with an efficiency of at least 80% when irradiated from any direction within ±20° of the normal to the surface of the outer layer; wherein at least one of the following:

[0118] (i) The power conversion device has a conversion efficiency of at least 30% for a first wavelength, which is a near-infrared wavelength between 700 nm and 1500 nm;

[0119] (ii) The outer layer of the power conversion device is configured to reflect or absorb a portion of the incident irradiation at a second wavelength, such that when irradiation passes through the outer layer from any direction between ±20° from the normal to the surface of the outer layer, less than 60% of the irradiation at the second wavelength reaches at least one junction, and the power conversion device has a conversion efficiency of less than 20% for the second wavelength, which is between 550 nm and 700 nm.

[0120] (iii) The outer layer of the power conversion device is configured to absorb or reflect at least a third wavelength such that when the power of the third wavelength is irradiated through the outer layer from any direction within ±20° of the normal to the surface of the outer layer, at least 50% of the power of the third wavelength is absorbed before reaching at least one junction, and the power conversion device has a conversion efficiency of less than 10% for the third wavelength, which is between 300 nm and 550 nm; and (iv) the power conversion device has a conversion efficiency of less than 5% for a fourth wavelength, which is between 1500 nm and 2000 nm.

[0121] Another embodiment of the power conversion device for converting an optical power beam into electrical power as described in this disclosure may include:

[0122] (i) A semiconductor device having a pn junction suitable for absorbing optical power beams.

[0123] (ii) A top conductor and a bottom conductor in electrical contact with a semiconductor device, wherein the top conductor covers a portion of the top surface of the semiconductor device, and

[0124] (iii) An optical layer disposed on the top surface of a semiconductor device, the optical layer comprising a top volume and a bottom volume, the bottom volume being in optical contact with the top surface of the semiconductor device and with the top conductor of the semiconductor device, and the top volume being in optical contact with air, wherein:

[0125] (a) The top conductor is adapted to reflect at least 30% of the light striking it.

[0126] (b) The optical layer has an optical density of less than 2 for the optical power beam, and

[0127] (c) The top conductor is adapted to direct at least 25% of the light reflected by the top conductor to a value greater than sin -1 Angle of (1 / refractive index of the bottom volume).

[0128] In such a power conversion device, at least a portion of the light reflected by the conductor can be reflected from the top surface of the top volume at an angle undergoing total internal reflection. The top volume of the optical layer itself can be an anti-reflective coating adapted to reduce reflections of the optical power beam from a medium having a refractive index of approximately 1. The top volume of the optical layer can also be a scratch-resistant coating. If it is an anti-reflective coating, it can be further adapted to reduce reflections of the optical power beam at angles between at least -10 degrees and +10 degrees from the normal to the top surface.

[0129] Additionally, in any of the power conversion devices described above, a portion of the coverage area of ​​the top surface covered by the top conductor may be at least 4%. The conductor itself may be made of metal and may include at least part of aluminum, gold, silver, or copper.

[0130] Furthermore, in the power conversion device described above, at least sin -1 The area of ​​the geometric projection of the portion of the conductor on the top surface of the semiconductor device, which is angularly aligned with (1 / refractive index of the bottom volume), can be at least 25% of the area of ​​the semiconductor device multiplied by the portion of the top surface covered by the top conductor.

[0131] According to another implementation of this power conversion device, laser reflection from the power conversion device can be diffused. In this case, the diffuse reflection from the power conversion device can have an angular subtense of at least 1.5 milliradians. Furthermore, in meters... 2The area of ​​the semiconductor device measured in units, multiplied by the square of the band gap of the junction measured in joules, multiplied by the cube of the maximum design power of the battery measured in watts, is less than 214 * 10^- ... -30 , making P 3 *(band gap) 2 A<214*10 -30 .

[0132] In any of the power conversion devices described above, the top conductor may include a conductive grid with a finger-shaped or triangular-shaped profile.

[0133] Finally, according to yet another implementation described in this disclosure, a power conversion device for converting optical power into electrical power is also provided, the power conversion device being adapted for optical wireless power transmission using a laser beam, the power conversion device comprising:

[0134] A photovoltaic cell having multiple conductors on a surface suitable for receiving a laser beam, the photovoltaic cell having at least one junction with a bandgap energy between 0.75 eV and 1.2 eV, and the photovoltaic cell having a cover layer disposed thereon;

[0135] in:

[0136] The capping layer includes a material adapted to absorb or reflect at least one of irradiation in the wavelength range of 550 nm to 700 nm, and transmits a laser beam toward the photovoltaic cell, wherein the wavelength of the laser beam is between 700 nm and 1500 nm; and

[0137] The transmittance of the coating layer for the wavelength of the laser beam is at least 50% higher than that for wavelengths in the range of 550 nm to 700 nm.

[0138] This makes the efficiency of the power conversion device in converting the laser beam into electrical power at the wavelength at least 2.5 times higher than that of the power conversion device at a wavelength of 550nm. Attached Figure Description

[0139] The invention will be more fully understood and appreciated in conjunction with the accompanying drawings and the following specific embodiments, wherein:

[0140] Figure 1 schematically illustrates a typical structure of a conventional photovoltaic cell.

[0141] Figure 2 The first two orders of Bragg reflection on a prior art rectangular grid photovoltaic cell of the type shown in Figure 1 are schematically illustrated.

[0142] Figure 3A representation of typical multi-order reflections from the surface of a photovoltaic cell is shown, where at least 20 order reflections are visible;

[0143] Figure 4A , Figure 4B and Figure 4C The diagram schematically illustrates the alternative grid outlines used in PV cells, and a schematic diagram of the reflected beam patterns generated by each outline;

[0144] Figure 5 Features of photovoltaic cells relevant to this disclosure are shown, and the terminology used is explained;

[0145] Figure 6A and Figure 6B The effect of the high refractive index coating on the incident angle of the incoming light beam impacting the photovoltaic cell is shown.

[0146] Figure 7A The effect of the shape of the cover layer and conductor fingers according to this disclosure on representative light rays impacting a photovoltaic cell is shown.

[0147] Figure 7B An implementation of a photovoltaic cell according to the present disclosure is shown, wherein an anti-reflective coating is added on either side of the cover layer;

[0148] Figure 7C and Figure 7D The diagram schematically illustrates the diagonal difference between the collimated beam and the diffuse beam striking the lens of the eye;

[0149] Figure 8A and Figure 8B The diagram schematically illustrates the reflection from the photovoltaic cell, and the path of the collimated beam of light as it strikes the human eye.

[0150] Figure 8C The schematic diagram illustrates the paths of some representative reflected and diffused light beams escaping from the capping layer of the photovoltaic cell in embodiments of this disclosure; and

[0151] Figure 9 A safety control system is shown for providing a warning in the following situation: a laser beam is expected to guide a beam with a specific power toward the direction of a receiver, but the receiver does not receive all or any of that power, indicating that the beam is turning in an unintended direction. Detailed Implementation

[0152] Referring now to Figure 1, a typical structure of a photovoltaic cell is schematically shown, which is made of a p-type semiconductor 13 attached to an n-type semiconductor 11, or sometimes very close to the n-type semiconductor 11 but separated by another layer, thus forming a pn junction 12. All-metal contacts are located on the back of the cell 14, and partially metal contacts 15 in the form of a grid (or similar structure) are located on the front of the cell, allowing light to penetrate the space between the conductors. Incident illumination generates a current 16 through the load.

[0153] Now for reference Figure 2 This schematically illustrates the first two orders of Bragg reflection of the incident beam 23 on a prior art rectangular grid photovoltaic cell 21. The incoming beam 23 strikes the metal grid 22 of the photovoltaic cell 21, and approximately 2-10% of the power in the beam 21 is reflected by the conductive grid 22 in a Bragg pattern comprising several orders, for example... Figure 2 The zeroth order 24 and the first order 25 are shown in the figure.

[0154] Now for reference Figure 3 This illustrates a typical representation of multi-order reflections 31 from the surface 32 of a prior art photovoltaic cell, where at least 20 orders of reflections are visible. The power in each "order" depends heavily on the angle of illumination, leading to safety and aiming issues. Total internal reflection spans approximately 5 degrees from the zeroth-order reflection, and the zeroth-order reflection is the strongest. Higher-order reflections involve significantly less power compared to lower orders. This differs from current cells, which preferably reflect to higher-order modes, particularly above the critical angle of the optical coating.

[0155] Now for reference Figure 4A , Figure 4B and Figure 4C , Figure 4A , Figure 4B and Figure 4C An alternative grid outline used in PV cells is schematically shown. Figure 4A The image shows a reflection from a grid on a rectangular conductor, generated at an angle opposite to the angle of the incoming beam. Figure 4B The reflection from a triangular reflector is shown, which splits the beam into two wide-angle beams and is suitable for a small field of view (FOV). Figure 4C The image shows reflection from a circular conductor, with the reflection spreading over a wide angle. A preferred implementation ( Figures 4A to 4C (Not shown) is a conductor covered with a diffuse top layer, which can diffuse radiation in a very wide pattern.

[0156] Figure 4B and Figure 4CThe structure shown, along with the diffuse coating on the conductor, enhances higher-order reflections from the grating and thus enhances the "recovery" of reflected light. It should be understood that perfect geometry is typically impossible to manufacture, and this illustration serves as a simple example. Preferably, a pattern that diffuses light over a wide field of view (FOV) is chosen, such as a diffuse, circular, or triangular shape. Shapes that reflect most of the light to a wide angle are preferred, for example, triangles with a reflector tilt greater than a threshold angle. The conductor is typically made of a reflective material (e.g., metal) that reflects at least 30% of the light falling upon it; typically, materials that reflect at least 90% of the light are chosen, such as aluminum, silver, or gold. The conductor may be coated with a diffuse coating.

[0157] Now for reference Figure 5 The terminology used in this disclosure is shown. Figure 5 The angle dependence of reflected light on the finger-shaped conductor on PV 51 is shown, depending on the incident light, and includes a back electrode and a pn junction in addition to conductor 52. Angle 55 is a local angle formed by the intersection of line 57, which is tangent to the surface of the finger-shaped conductor at point 56 on the conductor, and normal 58. The area of ​​conductor 52 projected onto the upper surface 59 of PV is shown below PV and numbered 53. The area of ​​conductor 52 projected onto the surface of PV by the portion of conductor 52 where the angle is less than a threshold is shown below PV and numbered 54.

[0158] Now for reference Figure 6A and Figure 6B , Figure 6A and Figure 6B The difference between the incident beam angle 61a of a known PV cell 62 without a high-refractive-index coating, as presented in this application, and the incoming beam angle 61b of a cell 64 with a high-refractive-index coating 63 is shown. Each PV cell is illuminated by a beam, the beam either being... Figure 6A Beam 61a in the middle, or Figure 6BThe light beam 61b passes through a cover layer 63, which is a transparent coating and is referred to as the optical cover layer. The top of the optical cover layer 63 may be coated with an anti-reflective coating to reduce reflection of the light beam 61b and allow most of the light beam 61b to enter the optical cover layer 63. The bottom surface 65 of the optical cover layer 63 contacts both the top of the PN junction of the battery 64 and a conductor (not shown) on the battery 64. An anti-reflective coating is present between the bottom 65 of the optical cover layer 63 and the battery 64, which is adapted to reduce reflection of the light beam 61b as it passes from the refractive index of the bottom portion 65 of the optical cover layer 63 to the top portion of the battery 64. The optical cover layer 63 typically has a high refractive index, preferably an optical density that allows at least 80% of the power to pass through it, and has an optical density <2 when measured for the light beam 61b. Due to the high refractive index of coating 63, beam 61b reaches the top surface of battery 64 at a reduced angle of incidence compared to the angle at which beam 61a, parallel to 61b, strikes battery 62. The thickness of coating 63 should be less than the width of battery 64.

[0159] Now for reference Figure 7A It shows a photovoltaic cell 71, which is similar to the one shown above. Figure 5 The photovoltaic cell shown in the figure has a capping layer 78 added. The figure illustrates the different paths an incident light beam can take when it strikes the PV structure. Beams 79a, 79b, 79c, and 79g are shown being absorbed by cell 71, as they would be in a known PV cell with the same conductor capping. Beam 79d, on the other hand, is shown being reflected by the side of conductor 72 and immediately absorbed by cell 71. Beam 79e is shown being reflected by the top of conductor 72 and escapes from the device in a manner similar to what would happen if it struck a rectangular conductor in the prior art. Therefore, beam 79e is lost and not converted into electrical energy. Beam 79f is shown being reflected from the conductor at an angle that would cause beam loss in a prior art PV cell. However, because the current PV is capped with capping layer 78, beam 79f now strikes the inside of the top surface of capping layer 78 at an angle of incidence greater than the critical angle of the top surface interface of capping layer 78, and is thus reflected back to the PV surface as beam 79f', and even in cases where… Figure 7AAfter the additional reflection typically shown, the beam of light is not lost but absorbed by the battery. The optical conductor 72 is wider than similar conductors in prior art batteries and therefore has lower resistance and higher reflectivity compared to prior art conductors. The shape of the optical conductor 72 is designed to maximize the projected area of ​​the portion of the conductor tilted at an angle greater than 80% of the critical angle, as calculated based on the refractive index of the bottom portion of the optical capping layer 78. Reflections at this angle are very likely to eventually reach the battery again and be absorbed and converted into electrical power. The conductor 72 typically has a reflectivity greater than 80% to 90%, but in some cases, the reflectivity of the conductor 72 may be lower. The conductor 72 can be made of metals such as aluminum, silver, gold, molybdenum, copper, nickel, or tungsten and can be coated with a diffusion coating, for example, an opal coating. Alternatively, the conductor can have small reflective structures or particles deposited thereon. The conductors 72 are spaced apart such that reflections from them are maximized to the order of 80% of the critical angle, as calculated based on the refractive index of the bottom portion of the optical capping layer 78. Such spacing is typically greater than 0.5 wavelengths per refractive index and less than 100 wavelengths.

[0160] Despite Figure 7A Previous Figure 5 and afterwards Figure 7B and Figure 8C The conductors in the diagram are shown in a finger shape, but it should be understood that the conductors may also have any other suitable profile (e.g., Figure 4B (A triangle) to provide multiple internal reflections of the light beam within the covering layer 78.

[0161] Now for reference Figure 7B It shows the following according to this disclosure Figure 7A The PV cell has anti-reflective coatings 73 and 74 added to the upper and lower surfaces of the cover layer 78.

[0162] Now for reference Figure 7C , Figure 7CThis illustrates the importance of the diagonal of the visual source, which is the angle relative to the source when viewed from a point in space. Specifically, the resolution of the human eye allows a typical retinal photoreceptor to observe a diagonal of approximately 1.1 milliradians of the surrounding environment. This calculation stems from the fact that the radius of the outer segment of a single retinal photoreceptor cell is approximately 25 micrometers, and the effective focal length of the human eye is approximately 17 millimeters in a water-based environment, equivalent to approximately 22 millimeters in air. A light source with a diagonal of 1.1 milliradians can be focused onto a single retinal cell, so the full power from the source can be absorbed by the same cell. Light sources with smaller diagonals will still be absorbed by a single photoreceptor. However, sources with larger diagonals cannot be focused onto small points of light due to poor optical quality. Therefore, it is impossible to focus such a source onto a single biological cell, thus sources with larger diagonals pose a smaller risk. In other words, a single retinal cell occupies approximately 4 x 10^6 meters of light. -6 The radiation from a diffuse source with a diagonal of 1.5 radians is expected to be distributed across at least two retinal cells, thus posing approximately half the risk to the retina and being safer.

[0163] Now for reference Figure 7C In detail, PV 71a diffusely reflects a portion of the light illuminating it. Lens 75 is located 100mm from the window surface in front of PV 71a, converging the light beam to a point 77 at the lens focal point. If PV 71a reflects a high-quality light beam (similar to a TEM), 00 (For a laser), lens 75 focuses the light onto a diffraction-limited spot. The relative angle 70 between the top of the image, the center of the lens, and the bottom of the image will be close to 0.

[0164] Another possible scenario is as follows Figure 7D As shown, PV 71a is a diffuse reflection image, rather than preserving the optical quality of the original laser beam. In this case, lens 75 will not produce a diffraction-limited spot, but will instead produce an image 76 of PV 71a, and the angle 70 will obviously be larger.

[0165] Typically, lens 75 moves around, closer to and away from the PV cell to locate the minimum diagonal point of the beam to determine the beam diagonal at a specific distance.

[0166] In addition to the requirements mentioned above, it is important that the PV cell responds to changes in illumination level. The higher the beam power, the more responsive the photovoltaic cell must be to allow safety systems to be based on the detected light level. It has been found that to make the PV cell responsive, the cell structure must be adjusted to match the expected power level according to the following formula:

[0167]

[0168] Where d is the thickness of the layer in the photovoltaic cell that absorbs photons of the light beam, measured in meters.

[0169] The band gap is the band gap energy of a pn junction, measured in joules.

[0170] A is in meters 2 Photovoltaic cell area measured in units.

[0171] If an excessively large battery is used, the battery's responsiveness will decrease, and it will not be able to react quickly enough to changes in the level of illumination.

[0172] Since d is typically less than 300 micrometers thick and always less than 1000 micrometers thick, the formula can be simplified to:

[0173]

[0174] Or in a more convenient form:

[0175] P 3 *(b band gap) 2 A<214*10 -30

[0176] Now for reference Figure 8A and Figure 8B ,in Figure 8A A reference PV cell 81a with known characteristics is shown, and Figure 8B This illustrates the effect of reflected, collimated laser light on the human eye. Figure 8A In this process, beam 84 illuminates PV cell 81a. Although most of the light is absorbed by cell 81a, some of the incident beam is reflected by the cell toward eye 85. Cell 81a typically reflects about 2-10% of the light that strikes it, with most entering first-order reflection, where light hitting a plane produces a mirror-like reflection with the angle of incidence equal to the angle of return. The reflected light is collected by the lens 88 of the human eye 85 and forms a series of discrete lines, which are the image of the conductor on the retina 86.

[0177] like Figure 8B As shown, the cornea and lens can focus the light band 89 from the collimated beam to a small point, potentially causing greater focal damage. Because reflections from the collimated beam will have minimal divergence, and because the beam is refracted by both the cornea 87 and the lens 88, the result is the focusing of a beam with powerful light energy (such as...). Figure 7C As shown in the diagram, this beam of light may be focused onto sensitive eye tissue. Such a focused beam of light has a high probability of causing damage at point 80 where the beam strikes the retina 86.

[0178] Now for reference Figure 8CThe diagram schematically illustrates a PV cell 81b according to a currently disclosed implementation. Unlike the PV cell 81a, the PV cell 81b uses a non-rectangular, highly convex conductor 82b and a cover layer 83. The cell 81b includes a conductor 82b that, being wider than a typical rectangular conductor, would normally reflect up to about 10% of light. However, because the conductor 82b reflects the beam at an angle, most of the first-order reflection is above the total internal reflection angle of the optical cover layer and is therefore reflected back to the cell, where about 90% is absorbed. Approximately 0.04%–2% of the original beam is reflected a second time by the conductor, and these rays 89b could be reflected outside the optical cover layer 83, but are now reflected diffusely. The eye's lens 88 collects a small amount of diffusely emitted light 89b and can form an image of the cell 81b on the retina. However, this image has a much lower power per unit area, thus posing a much smaller risk to the retina. The eye's highest light collection will occur at the minimum distance. Since the minimum focal length of the human eye is about 100-150mm, the most dangerous collection position would be about 100-150mm away from the battery.

[0179] will come from Figure 8A The reflected light from the reference PV cell and Figure 8C In comparison to the schematic depiction of an implementation of this disclosure, the beam 84 approaches the battery 81b from the same angle as the angle at which it impacts the battery 81a, as shown. In contrast, in... Figure 8C In this process, the light beam passes through the cover layer 83 at an angle above 80% of the critical angle before being reflected by conductor 82b, as calculated based on the reflectivity of the bottom of the cover layer 83. The reflected light is absorbed by cell 81b with higher efficiency than that of cell 81a, and the percentage of the light beam ultimately emitted through the top of the optical cover layer 83 is lower compared to the percentage reflected by conductor 82a. Furthermore, the light rays 89b emitted from the top of the optical cover layer 83 are diffused, each emitted in a different direction. Therefore, compared to the light emitted by... Figure 8A Compared to the power of light collected by the eye in the middle, Figure 8C The power of the light that struck the eye was relatively low. Figure 8C In this process, because light rays do not travel in the same direction, they do not converge at the same point, thus forming a diffuse image on the retina at 85 degrees of the eye (e.g., ...). Figure 7D (As shown in the image), this poses a much smaller risk to the retina.

[0180] The device described herein typically allows a 1cm x 1cm battery to reflect diffuse back reflections, such that when focused by an f = 25mm lens (diameter-oriented, at least 1.5mRad, and typically more) placed 100mm from the battery surface, the back reflections from the conductor are reflected onto the TEM. 00The reflection of the laser beam will form a minimal image, thus posing a much smaller risk to the retina. Furthermore, by diffusing the beam, the current cell configuration allows the typically center-weighted beam received from the laser source to be less concentrated and more uniform. Therefore, improved illumination uniformity allows for more complete cell utilization by allowing current to flow from a shorter distance to the collector at the cell's edge. The current cell also allows for thicker metallic conductive fingers, resulting in lower ohmic losses, a favorable feature in high-flux applications, as is the case with most laser power converters.

[0181] Now for reference Figure 9 The diagram illustrates a safety control system 90 configured to provide warnings in scenarios where a transmitter 95 (typically a laser) is expected to direct a beam of light with a specific power toward a receiver 91, but the receiver does not receive all or any of that power, indicating that the beam is being redirected in an unintended direction. The control system 90 provides an indication or warning that the transmitted laser beam may pose a hazard to the surrounding environment because it has not reached its intended receiver, or is reaching the correct receiver but with insufficient power. The controller unit 97 is most advantageously located within the transmitter 95, but may also be located elsewhere in the system (e.g., Figure 9 (As shown in the diagram), or located in the space served by the transmitter, the receiver receives signal input 92 from detection unit 91 (typically a PV cell in the receiver). Signal 92, sampled from the electrical power output 93 of the PV cell, represents the power level of the portion of the PV cell that falls on the PV cell during illumination with the laser wavelength, even in scenarios where a significant power level from other sources (e.g., sunlight 94) might fall on the PV cell 91. Control unit 97 is configured to also receive signals from laser power supply 95 in the transmitter, indicating the power of the laser beam emitted by the laser and from the position of scanning mirror 96. Both settings of these components of the system are determined by the operational requirements for supplying the laser beam power to the receiver. If the laser power setting and scanning mirror position indicate that the detector unit expects a certain power level, and the power level displayed to the control unit is lower than that expected level by a predetermined amount, it is assumed that a portion of the beam is blocked and has not reached its intended receiver target, thus triggering a safety warning by the system.

[0182] It should be understood that the control system can also operate in its conventional manner (i.e., in the opposite direction) to optimize the scanning mirror settings, center the laser beam around the receiver PV, and control the laser to provide the expected laser power based on the power measured by the detector unit.

[0183] It will be recognized by those skilled in the art that this invention is not limited to the content specifically shown and described above. Rather, the scope of this invention includes both combinations and sub-combinations of the various features described above, as well as variations and modifications that would occur to those skilled in the art upon reading the above description and that are not found in the prior art.

Claims

1. A power conversion device for converting optical power into electrical power, the power conversion device being adapted for optical wireless power transmission using a laser beam, the power conversion device comprising: A photovoltaic cell having a plurality of conductors on a surface suitable for receiving the laser beam, the photovoltaic cell having at least one junction having a bandgap energy between 0.75 eV and 1.2 eV; as well as A cover layer, comprising a top volume and a bottom volume, is disposed on the photovoltaic cell, the bottom volume being in optical contact with the surface of the photovoltaic cell, and the top volume being in optical contact with air. The cover layer comprises a material adapted to limit the transmission of irradiation by absorption or reflection and to transmit the laser beam toward the photovoltaic cell, the irradiation having a wavelength outside the wavelength range of the laser beam. in: The wavelength of the laser beam is in a first range between 700 nm and 1500 nm; The transmittance of the cover layer to the wavelength of the laser beam is at least 50% higher than the transmittance of the cover layer to wavelengths in the second range of 550 nm to 700 nm, such that the efficiency of the power conversion device in converting the laser beam to electrical power at the wavelength of the laser beam is at least 2.5 times higher than the efficiency of the power conversion device at the wavelength of 550 nm. The capping layer is further configured to absorb or reflect wavelengths in a third range of at least 300 nm to 550 nm, such that when the capping layer is irradiated from any direction between ±20° and the normal to the outer surface of the capping layer, at least 50% of the power of the wavelengths in the third range is absorbed before reaching the at least one junction, and the power conversion device has a conversion efficiency of less than 10% for the wavelengths in the third range; and The power conversion device has a conversion efficiency of less than 5% for wavelengths in the fourth range between 1500nm and 2000nm.

2. The power conversion device according to claim 1, wherein, The bandgap energy is tuned to the wavelength of the laser such that for any wavelength at least 25% longer than the wavelength of the laser, the efficiency of converting optical power to electrical power is less than one-quarter of the efficiency of conversion at the laser wavelength.

3. The power conversion device according to any one of claims 1 and 2, wherein, The covering layer also includes at least one of the following: A first anti-reflective coating is disposed on the outer surface of the cover layer remote from the photovoltaic cell. This first anti-reflective coating is adapted to reflect irradiation and allow the laser beam to penetrate into the cover layer, wherein the irradiation has a wavelength outside the wavelength range of the laser beam. A second anti-reflective coating is disposed between the surface of the photovoltaic cell and the cover layer. The second anti-reflective coating is adapted to reflect irradiation and allow the laser beam to be transmitted into the photovoltaic cell, the irradiation having a wavelength outside the wavelength range of the laser beam.

4. The power conversion device for converting optical power into electrical power according to claim 1, wherein: The plurality of conductors are adapted to reflect at least 30% of the light striking them; The covering layer has an optical density of less than 2 for the optical power beam; as well as The plurality of conductors are adapted to guide at least 25% of the light they reflect to a direction greater than sin -1 (1 / the angle of the refractive index at the inner surface of the coating layer).

5. The power conversion device according to claim 4, wherein, At least a portion of the light reflected by the plurality of conductors is reflected from the outer surface of the cover layer at an angle undergoing total internal reflection.

6. The power conversion device according to any one of claims 1 and 2, wherein, The top volume of the overlay includes an anti-reflective coating adapted to reduce reflections of the optical power beam from a medium with a refractive index of 1.

7. The power conversion device according to any one of claims 1 and 2, wherein, The top volume of the cover layer includes a scratch-resistant coating.

8. The power conversion device according to claim 4 is further adapted to reduce the reflection of the optical power beam at an angle between at least -10 degrees and +10 degrees from the normal of the outer surface of the top volume.

9. The power conversion device according to any one of claims 1 to 8, wherein, The plurality of conductors cover at least 4% of the surface of the photovoltaic cell.

10. The power conversion device according to any one of claims 1 to 2, wherein, The multiple conductors are made of metal.

11. The power conversion device according to claim 10, wherein, The plurality of conductors include at least partially aluminum, gold, silver or copper.

12. The power conversion device according to claim 4, wherein, With at least sin -1 The area of ​​the geometric projection of the portion of the plurality of conductors on the surface of the photovoltaic cell, which is (1 / refractive index at the inner surface of the cover layer) at an angle aligned with the photovoltaic cell, is at least 25% of the area of ​​the photovoltaic cell multiplied by the portion of the coverage area of ​​the surface covered by the plurality of conductors.

13. The power conversion device according to any one of claims 1 and 2, configured such that laser reflection from the power conversion device is diffuse reflection.

14. The power conversion device according to claim 13, wherein, The diffuse reflection from the power conversion device has a diagonal of at least 1.5 milliradians.

15. The power conversion device according to any one of claims 1 and 2, wherein, With rice 2 The area of ​​the photovoltaic cell measured in units, multiplied by the square of the junction band gap measured in joules, multiplied by the cube of the cell's design maximum power measured in watts, is less than 214 * 10^- ... -30 , making P 3 *(band gap) 2 A<214*10 -30 .

16. The power conversion device according to any one of claims 1 and 2, wherein, The plurality of conductors include a conductive grid having any one of the following: (i) a finger-shaped profile; (ii) a triangle-shaped profile; or (iii) a convex profile.

17. A security system for a wireless optical power transmission system, comprising a transmitter, a receiver, and a control unit, wherein: (i) The transmitter includes: Lasers suitable for emitting beams; and A scanning mirror adapted to guide the light beam toward the receiver; (ii) The receiver includes the power conversion device for converting optical power to electrical power as claimed in claim 1; and (iii) The control unit is adapted to receive first data indicating the position of the scanning mirror and second data indicating the power of the beam emitted by the laser from the transmitter, and to determine the desired power incident on the photovoltaic cell based on the first data and the second data, and to compare the desired power with the power of the laser beam impacting the receiver as measured by the photovoltaic cell, and to indicate a potential safety problem if the desired power deviates from the measured power by more than a predetermined level.

18. A power conversion device for converting optical power into electrical power, the power conversion device being adapted for optical wireless power transmission using a laser beam, the power conversion device comprising: A power conversion device having at least one junction having a bandgap energy between 0.75 eV and 1.2 eV, and having an outer layer through which laser light is transmitted toward the at least one junction, the outer layer being configured to transmit at least a first wavelength into the at least one junction with an efficiency of at least 80% when irradiated from any direction within ±20° of the normal to the outer surface of the outer layer; wherein: The power conversion device has a conversion efficiency of at least 30% for the first wavelength, which is a near-infrared wavelength between 700 nm and 1500 nm. The outer layer of the power conversion device is configured to reflect or absorb a portion of the incident irradiation at a second wavelength, such that when irradiation passes through the outer layer from any direction within ±20° of the normal to the outer surface of the outer layer, less than 60% of the irradiation at the second wavelength reaches the at least one junction, and the power conversion device has a conversion efficiency of less than 20% for the second wavelength, which is between 550 nm and 700 nm. The outer layer of the power conversion device is configured to absorb or reflect at least a third wavelength, such that when the power of the third wavelength is irradiated through the outer layer from any direction within ±20° of the normal to the outer surface of the outer layer, at least 50% of the power of the third wavelength is absorbed or reflected before reaching the at least one junction, and the power conversion device has a conversion efficiency of less than 10% for the third wavelength, wherein the third wavelength is between 300 nm and 550 nm; and The power conversion device has a conversion efficiency of less than 5% for the fourth wavelength, which is between 1500 nm and 2000 nm.

19. A power conversion device for converting optical power into electrical power, the power conversion device being adapted for optical wireless power transmission using a laser beam, the power conversion device comprising: A photovoltaic cell having a plurality of conductors on a surface suitable for receiving the laser beam, the photovoltaic cell having at least one junction having a bandgap energy between 0.75 eV and 1.2 eV, and the photovoltaic cell having a cover layer disposed thereon; in: The covering layer includes a material adapted to absorb or reflect at least one of irradiation in the wavelength range of 550 nm to 700 nm, and to transmit the laser beam toward the photovoltaic cell, wherein the wavelength of the laser beam is between 700 nm and 1500 nm. The transmittance of the capping layer to the wavelength of the laser beam is at least 50% higher than the transmittance of the capping layer to wavelengths in the range of 550 nm to 700 nm, such that the efficiency of the power conversion device in converting the laser beam to electrical power at the wavelength of the laser beam is at least 2.5 times higher than the efficiency of the power conversion device at a wavelength of 550 nm; and The power conversion device has a conversion efficiency of less than 5% for wavelengths between 1500nm and 2000nm.

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