WO2018049277A1

WO2018049277A1 - Systems, methods and devices for applying high frequency, electric pulses to semiconductor materials, including photovoltaic cells

Info

Publication number: WO2018049277A1
Application number: PCT/US2017/050843
Authority: WO
Inventors: Santosh Kumar; Naresh Sharma
Original assignee: UltraSolar Technology, Inc.
Priority date: 2016-09-09
Filing date: 2017-09-08
Publication date: 2018-03-15

Abstract

A system can include a resonant cavity formed with at least one cavity surface formed by a pyroelectric material, the resonant cavity configured to generate electrical pulses when resonating in response to receiving electromagnetic waves having at least one predetermined frequency; and at least one photovoltaic (PV) cell coupled to receive the electrical pulses while exposed to photons.

Description

SYSTEMS, METHODS AND DEVICES FOR APPLYING HIGH FREQUENCY, ELECTRIC PULSES TO SEMICONDUCTOR MATERIALS, INCLUDING PHOTOVOLTAIC CELLS

TECHNICAL FIELD

The present disclosure relates generally to the modification of semiconductor materials by application of electric fields, and more particularly to the application of high frequency pulses to semiconductor-based photovoltaic cells to alter photon absorption spectra.

BACKGROUND

With the widespread adaptation of solar energy as a substitute for the environmentally damaging fossil fuel based energy, the cost of solar energy continues to drop significantly. However, in order to further increase the adaptation of such clean energy sources, it remains a continuing goal to further bring the cost of solar energy down. One conventional approach has been to attempt to utilize custom materials to capture hot carriers generated by photons that would otherwise be lost. Such conventional approaches are sometimes referred to as Hot Carrier Solar Cells (HCSC).

Hot carriers are the electrons and holes generated upon the absorption of photons with energy above the conduction band of the photovoltaic (PV) material. For example, in silicon, a photon with wavelength lower than 650 nm (1.9 eV) generates hot carriers upon being absorbed by silicon. These hot carriers have a lifetime on the order of pico-seconds. A typical silicon based PV cell requires a lifetime of about 200 Ds for a carrier to travel to an electrode. Accordingly, such hot carriers are not collected at the PV cell electrode and do not contribute the PV cell generated current.

Hot carriers are not stable because no quantum state is available in the PV material at those energy levels. Therefore, hot electrons will lose their energy and drop to a more stable state, (e.g., the bottom of the conduction band). The energy lost by the electrons in this process is dissipated mostly as heat (i.e., thermalization).

Conventional approaches seeking to capture hot carriers before thermalization have included employing complex materials and structure optimization. Such approaches can be expensive and time consuming.

SUMMARY

According to embodiments, high frequency (HF) pulses (e.g., greater than 1 GHz) can be applied to a semiconductor based photovoltaic (PV) cell to increase the amount of PV current generated by the PV cell. In some embodiments, HF electric pulses can be generated by a pyroelectric based resonant cavity.

According to embodiments, additional, temporary quantum states can be formed in a semiconductor material by application of HF electric pulses. In some embodiments, HF electric pulses can be generated by a resonant cavity.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a block schematic diagram of a system according to an embodiment.

FIG. 2 is a block schematic diagram of a pyroelectric resonant cavity that can be included in embodiments.

FIGS. 3A and 3B are diagrams of another pyroelectric resonant cavity that can be included in embodiments.

FIG. 4 is a block schematic diagram of another system according to an embodiment. FIG. 5 is a block schematic diagram of a solar power generation system according to an embodiment.

FIG. 6 is a block diagram of a solar power generation system according to another embodiment.

FIG. 7 is a diagram showing contacts to a semiconductor PV cell that can be included in embodiments.

FIG. 8 is a diagram showing contacts to a semiconductor PV cell that can be included in embodiments. FIGS. 9A and 9B are diagrams showing a retrofitted system and method according to an embodiment.

FIG. 10 is a flow diagram of a method according to an embodiment.

FIG. 1 1 is a flow diagram of a method according to another embodiment.

FIG. 12 is a flow diagram of a method according to a further embodiment.

FIG. 13 is a graph showing energy of states as a function of frequency of applied pulses.

FIG. 14 is a graph showing energy of states as a function of frequency and peak voltage.

FIG. 15 is a graph showing l-V curves for a silicon based solar cell with and without the application of high frequency (HF) electric pulses.

FIG. 16 is a graph showing Additional absorption peaks that can appear on application of the electric pulses to a semiconductor.

FIGS. 17-19 are diagrams showing photoluminescence emission with the application of HF pulses.

FIG. 20 is a simplified energy band diagram showing quantum states.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments described herein show the application of high frequency electric pulses (e.g., greater than 1 GHz) to semiconductor materials to alter the photoelectric properties of the semiconductor material. According to embodiments, such electric pulses can be generated with a resonant cavity having one or more surfaces formed by a pyroelectric material. According to embodiments, such electric pulses can be applied to a semiconductor based photovoltaic (PV) cell, to increase the amount of current generated by the PV cell when exposed to photons.

According to embodiments, the application of high frequency electric pulses to a semiconductor based PV cell can create additional states that enable the capture of hot carriers, increasing the amount of energy generated by the PV cell as compared to the absence of such electric pulses.

According to embodiments, a system can include a pyroelectric based pulse generator that applies high frequency pulses to a semiconductor PV cell to increase the range of photons that can be absorbed to generate the PV cell current.

FIG. 1 shows a system 100 according to one embodiment. A system 100 can include a high frequency (HF) pulse generator 102 a PV cell 104. A HF pulse generator 102 can generate HF electric pulses 1 10 in one or more frequencies, where such frequencies are greater than 1 GHz. In some embodiments, HF electric pulses 110 are greater than 10 GHz. HF electric pulses 1 10 can be received by PV cell 104. In response PV cell 104 can have a different response when exposed to photons as compared to the absence of HF electric pulses 1 10. In particular embodiments, a PV cell 104 response can be an increase in power generation as compared to the absence of HF electric pulses 110 (given the same exposure to light).

In addition or alternatively, a system 100 can include a HF pulse generator 102 that generated electric pulses at one or more frequencies that create temporary, additional quantum states in the PV cell 104 that enable additional spectra to be absorbed in the generation of PV cell 104 current. In particular embodiments, additional quantum states can enable the capture of hot carriers that might otherwise be lost to thermalization. Frequencies of HF electric pulses 1 10 can vary according to PV cell material. The derivation of frequencies giving rise to additional quantum states is described at a later point herein.

In addition or alternatively, a system 100 can be a pulse generator 102 that includes a pyroelectric based resonant cavity. A pyroelectric based resonant cavity can include one or more cavity surfaces formed by a pyroelectric material. The pyroelectric materials response to resonance in the cavity can be rise to electric pulses. In some embodiments, such a resonant cavity can be designed to resonate at one or more infrared (IR) frequencies (i.e., form standing IR waves).

A PV cell 104 can be a semiconductor based PV cell, including one or more semiconductor layers. Such semiconductor layers can be monocrystalline, polycrystalline, or amorphous. Further, such semiconductor layers can be a single species semiconductor or a compound semiconductor. HF electric pulses can have a frequency (or frequencies) selected based on the response of the semiconductor material. In very particular embodiments, a PV cell can be a silicon based PV cell, more particularly, a monocrystalline silicon PV cell.

FIG. 2 is a side cross sectional representation of a HF electric pulse generator 202 that can be included in embodiments. HF pulse generator 202 can be a resonant cavity that generates electric pulses 210 in response to incident electromagnetic waves 208. HF pulse generator 202 can include a number of layers 206-0/1/2 stacked on top of one another. One or more layers 206-0 can be formed of a pyroelectric material. In very particular embodiments, one or more layers 206-0/1/2 can be formed from a perovskite-type material. In operation, the materials and geometry of a resonant cavity are selected to give rise to a standing wave that can generate a desired frequency or frequencies.

FIGS. 3A and 3B are side cross representations of a HF electric pulse generator 302 that can be included in embodiments. FIG. 3A is a cross sectional view taken along line A-A of FIG. 3B, and FIG. 3B is a cross sectional view taken along line B-B of FIG. 3A.

HF pulse generator 302 can be a resonant cavity that generates electric pulses 310 in response to incident infrared light. In a particular embodiment, pulse generator 302 can be one implementation of that shown in FIG. 2. Pulse generator 302 can include layers 306-0/1/2, isolation structures 312, DC bias source 314, and contact 316. Layers 306-0 can be formed of a pyroelectric material, and thus generate electrical charge in response to variations in temperature. Layer 306-2 can be a material having a different index refractive index than that of layer 306-0. In the particular embodiment shown, layers 306-0 and 306-1 can have the same refractive index (n1) while middle layer 306-2 can have a different refractive index (n2) than layers 306-0/1. In some embodiments, all three layers (306- 0/1/2) can be formed from pyroelectric materials. In very particular embodiments, layers 306-0/1 can be formed of one pyroelectric material having one refractive index while layer 306-02 can be formed of a different pyroelectric material having a different refractive index.

The materials and geometry can be selected to give rise to standing I R waves in the resonant cavity. The varying amplitude of such waves can result in varying temperature. The varying temperature can create charging nodes in the pyroelectric material due to the pyroelectric effect. DC bias source 314 can drive the charge created at the charge node to generate electrical pulses. The electrical pulses can be output via electrode 316. According to embodiments the resonant cavity can be sized to support only certain TE modes (those giving rise to the desired standing wave(s)). A length of the resonant cavity can be sized to allow only a single phase of the standing wave. FIG. 3A shows a representation of a standing wave 31 1 in resonant cavity.

As shown in FIG. 3B, in some embodiments, desired geometry for the resonant cavity can be achieved by patterning layers 306-0 and 306-2 on layer 306-1 , and forming isolation structures 312 between such patterned layers.

FIG. 4 is a block schematic diagram of a system 400 according to another embodiment. A system 400 can include a pyroelectric based HF pulse generator subsystem 418 (pyroelectric subsystem) and a PV cell 404.

Pyroelectric subsystem 418 can be single physical unit that contains components for generating HF electrical pulses. In the embodiment shown, pyroelectric subsystem 418 can include a pyroelectric resonant cavity 402 and DC bias unit 414. Such components can take the form of any of those described herein, or equivalent.

Optionally, pyroelectric subsystem 418 can include signal conditioner 420 and impedance matching section 422. Signal conditioner 420 can adjust signals generated by pyroelectric resonant cavity 402. Such adjustments can include any suitable adjustment, including but not limited to altering pulse shape, filtering, amplification, etc. Impedance matching section 422 can enable an impedance of a signal path carrying HF electrical pulses generated from pyroelectric resonant cavity 402 to reduce reflection, according to any suitable technique.

PV cell 404 cam take the form of any of those shown herein, or equivalents.

While embodiments can take various forms, some embodiments can include systems for generating power. FIG. 5 is a system 500 according to another embodiment. A system 500 can include a pyroelectric resonant cavity 502 and pyroelectric subsystem 518, one or more solar panels 504, and a power system interface 506. A pyroelectric resonant cavity/subsystem 502/518 can take the form of any of those shown herein, or equivalents.

Solar panel(s) 504 can include semiconductor PV panels as described herein, or equivalents, be coupled to receive electric pulses generated by cavity/subsystem 502/518.

Power system interface 506 can form all or part of a power generation system that generates power 509 from current provided by solar panel(s) 504. While such power can take any suitable form, including DC power, in one particular embodiment, power system interface 506 can include an inverter (and optionally one or more combiners) to provide AC power.

FIG. 6 is a block diagram of a system 600 according to another embodiment. A system 600 can be a solar power system that can generate AC power at greater efficiency than conventional systems. A system 600 can include solar panels 604, pyroelectric subsystems 618-0/1 , combiner/inverter subsystem 606, and transient suppressor 624. Solar panels 604 can be silicon based PV panels, in particular embodiments, crystalline silicon PV panels. Panels 604 can be exposed to sunlight 625 to generate a PV current. However, unlike conventional approaches, while generating PV current panels 604 can also be subject to electric pulses 610-0/1 generated by pyroelectric subsystems 618-0/1. Due to such electric pulses 610-0/1 solar panels 604 can convert a greater spectrum of sunlight to PV current, as compared to the solar panel without the electric pulses. In particular embodiments, electric pulses can be HF electric pulses.

A discussion of the basis for such increased PV current is described below in more detail.

Pyroelectric subsystems 618-0/1 can take the form of any of those described herein, or equivalents.

Pyroelectric subsystems 618-0/1 can include one or more pyroelectric resonant cavities for generating HF electric pulses as described herein or equivalents. While FIG. 6 shows a particular ratio of pyroelectric subsystems 618-0/1 to solar panels 604, this should not be construed as limiting in any way. The ratio can be greater or smaller, including more than one pyroelectric subsystems 618-0/1 to a solar panel. As but one example, there can pyroelectric subsystems that provide electric pulses at different frequencies, and both such pulses can be applied to a same solar panel. In such embodiments, the different electric pulses may or may not be HF electric pulses.

A transient suppressor 624 can be suppress transients generated by the electric pulses being applied to the solar panels 604, and prevent such transients from reaching combiner/inverter 606. Combiner/inverter 606 can combine outputs from solar panels 604, and provide them to an inverter, which can generate AC power 609.

It is noted that pyroelectric subsystems 618-0/1 and transient suppressor 624 can be entirely external to the solar panels, and thus advantageously deployable in a balance of system (BOS) area. As will be noted below, this can make embodiments easily deployable to retrofit into existing solar generation sites, replace existing solar generation sites, and/or compatible with planned solar generation sites.

While some embodiments can apply electrical pulses to a PV cell by way of the same contacts through which a PV cell current flows, in other embodiments, electrical pulses can be applied to a PV cell via contacts separate from those that provide the PV cell current for power generation.

FIG. 7 is side cross sectional view showing a portion of PV cell 704 that can be included in embodiments. A PV cell 704 can include semiconductor regions 734, a charge storing layer 730 and/or anti reflective coating (ARC) layer), and optionally, an insulating layer 732.

PV cell 702 can include different types of contact electrodes, including first contact electrodes 726 and second contact electrodes 728. First contact electrodes 726 can be used for the flow of generated photoelectric current, but may not be used to apply electric pulses. Second contact electrodes 728 can be used to apply electric pulses, but may not be used for passage of a photoelectric current. In particular embodiments, second contact electrodes 728 can apply electric pulses generated with a pyroelectric based resonant cavity, including HF electric pulses.

FIG. 8 is side cross sectional view, showing a portion of PV cell 804 that can be included in embodiments.

A PV cell 804 can include items like those of FIG. 7, including semiconductor regions 834, a charge storing (and/or ARC) layer 830, and optionally, an insulating layer 832.

PV cell 804 can differ from that of FIG. 7 in that contact electrodes can be on a bottom surface (i.e., surface not directly facing a light source). As in the case of FIG. 7, PV cell 804 can include first contact electrodes 836 and second contact electrodes 838. Frist contact electrodes 836 can be used for the flow of photoelectric current, and not for the application of electric pulses. Contact electrodes 838 can be used to apply electric pulses, but not used for passage of a photoelectric current.

While embodiments can include systems that inherently include pyroelectric subsystems as described herein, alternate embodiments can include methods of retrofitting existing solar power systems to enhance their performance. One such embodiment is shown in FIGS. 9A and 9B. FIG. 9A shows a conventional solar power system 901. One or more solar panels 904 can generate a current, which can be applied to an inverter (and combiner in the case of multiple panels) 906, which can output usable AC power.

FIG. 9B shows a retrofitting method. A pyroelectric resonant cavity 902, or subsystem based on such a cavity, can be connected to solar panel(s) 904. Such a connection can apply electric pulses, including HF electric pulses, to a semiconductor in such solar panels 904 to increase overall absorption spectra, thereby increasing overall PV current. In the embodiment shown, a transient suppressor 924 can also be installed between the solar panel(s) and inverter (optionally with combiner) 906. Resulting power 909 generated by the system 900 can be greater than that generated by conventional system 901.

In this way, conventional solar power systems can be upgraded to increase power generation efficiency. While embodiments above have shown various systems and methods, additional methods will now be described.

FIG. 10 is a flow diagram showing a method 1000 according to an embodiment. A method 1000 can includes generating electric pulses with a pyroelectric based resonant cavity 1000-2. In some embodiments, such pulses can be HF electric pulses. In some embodiments, electric pulses can be generated with any of the various systems and system components disclosed herein.

Generated electric pulses can be applied to a PV cell while the PV cell is exposed to light 1000-4. A PV current can then be generated with the PV cell 1000-6. In some embodiments, a PV current can be greater than if the PV cell was exposed to the same light source, but not subject to the electric pulses.

FIG. 1 1 is a flow diagram of another method 1100 according to an embodiment. A method 1 100 can include generating electric pulses with a pyroelectric based resonant cavity 1100-2, like that shown as 1000-2 in FIG. 10. The generated electric pulses can be applied to a semiconductor material to generate additional absorption states 1100-4 in the material. Absorption states can be states that enable a photon to generate an electron hole pair that can result in PV current in the semiconductor material. In particular embodiments, the semiconductor material can include one or more p-n junctions. A PV current can be increased by photons corresponding to the additional photon states 1100-6, as compared to a PV current without such additional states.

FIG. 12 is a flow diagram of a method 1200 according to another embodiment. A method 1200 can include generating electrical pulses greater than 1 GHz 1200-2. Such an action can include any suitable pulse generation method, but in particular embodiments can utilize a pyroelectric based resonant cavity as described herein.

Electrical pulses can include more than one frequency, with at least one frequency being greater than 1 GHz, in particular embodiments greater than 10 GHz.

The electrical pulses greater than 1 GHz can be applied to a silicon based PV cell to generate additional photon absorption states 1200-4. A current of a PV cell can be increased due to such additional photon states 1200- 6. A PV current can be filtered to generate a filtered PV current 1200-8. Such action can include reducing or substantially eliminating transient spikes that can arise from the application of the electrical pulses. Power can then be generated from the filtered PV current 1200-10.

Embodiments can take various forms, and work according to various principles. In some embodiments, high frequency electric pulses can be applied to semiconductor materials to capture hot-carriers that would otherwise be lost to thermalization. In particular, high frequency pulses can be applied to an entire crystal of a PV cell. The effect of applying such electric pulses, which can be multi-frequency pulses, can capture hot-carriers that might otherwise be lost to thermalization, and thus enhance PV cell efficiency.

A possible mechanism utilized in some embodiments can be the generation of temporary quantum states in a conduction band of a semiconductor crystal by application of electric pulses can generate temporary quantum states in a conduction band of a semiconductor crystal. In particular embodiments, the crystal can be silicon, and hot carriers can be held for more than 200 με. It is believed such effects can be achieved by high frequency electric pulses disturbing the equilibrium of electric potential due to atoms in the lattice.

A theoretical model of this phenomenon has been developed by modifying the Bloch function and the

Hamiltonian operator in the Schrodinger equation to calculate the energy states. It is shown that the model predicts creation of these energy states for only certain frequencies.

Energy bands are created in a lattice by interaction of electric potentials of the individual atoms or molecules forming the lattice sites. In silicon, the bond energy is 2.3 eV. A DC electric field applied to silicon with energy comparable to the bond energy has the potential to impact the electrical potential of the matrix. A high frequency oscillating electric field (pulses) can impact the electric equilibrium and can introduce permissible energy states.

In the following model, the Bloch potential for the lattice has been altered by adding a dynamic potential component from the incoming high frequency electric pulses. We have also used the pulse potential as an operator to alter the Hamiltonian of the lattice as the pulses will alter the way the potentials interact with each other.

The Bloch function for a periodic potential is given by:

where k is the wave vector and r is the lattice vector; DDm is the potential between sites a and m; and CD(k) is a constant depending upon a and k.

The time independent Schrodinger Equation for this Bloch function is

.∑_» Hm !$ s) £<si&? ⁼ ¾s«..¾ where the Hamiltonian, H is given by

Here, V(r) is the static potential at the lattice site (r).

The Hamiltonian in gets impacted by the externally applied pulsed electric field. Thus, the extra potential from the high frequency pulses is time dependent and can be expressed as

ψ«. = where cp_u is the additional potential from the applied pulsed electric field; cp_p is the maximum pulse height; ω is the pulse frequency; and f is the time.

Then the Bloch function can now be expressed as: It is to be noted that the mass m must be replaced by effective mass μ for the time dependent case. Then using the above e

Below is the analytical solution for the energy of the new state(s).

where a and b are constants, Δρ_ρ is the charge density in the lattice due to the pulses and At is the minimum time that the new energy state has to exist in order to increase the power output of the cell. In this analysis, we have used 200 micro-seconds as the value for At. The above equation relates the creation of metastable states with the applied electric pulses. We have used this equation to predict the generation of new states dependent upon applied frequency of the pulses which has been further experimentally validated.

FIGS. 13 and 14 are obtained by solving the above equation.

FIG. 13 shows energy of states as a function of the frequency of applied pulses. In FIG. 13, the pulse potential (height) used in the calculation is 100 mV and the charge density is assumed to be 206 C/m³.

FIG. 14 shows the model prediction for different peak voltages of the pulses. Peak pulse voltage impact on the energy of states is shown. It is clear from figure that at very high frequencies (above a THz), no energy states are created.

Applicant stresses that the above derivation is for a silicon crystal, but embodiments are not limited to such a material. One skilled in the art would realize that different materials would have different responses.

The correlation between the energy levels of these states and the frequency of the applied pulses has been experimentally demonstrated.

In experiments, mono and poly-crystalline silicon solar cells were connected to a high frequency generation device and changes in the cell behavior were observed using a) l-V testing, b) absorption spectroscopy and 3) photoluminescence.

The high frequency pulses were generated using a Fabry-Perot etalon made of biased Pyroelectric thin films. Measurement of the frequency was done using waveguide based frequency meter. The device uses a resonant cavity. The resonant frequency of the cavity was varied by means of a plunger, which was mechanically connected to a micrometer mechanism. Movement of the plunger into the cavity reduces the cavity size and increases the resonant frequency. Conversely, an increase in the size of the cavity (made by withdrawing the plunger) lowers the resonant frequency. High frequency pulses are made incident on the solar cell through a cable which essentially works as an antenna. The cell is connected to the source of high frequency pulses using this method for about five minutes before the experiments are performed. l-V measurements were made on one sample of c-Si solar cell before and after exposure to the pulses. A Solar Light solar simulator was used at 0.5 Sun intensity for illumination. A current source (2A max) was used for voltage and current measurements. I-V test of the solar cell was carried out in a flash test mode (i) first without connecting to frequency generating device, (ii) with frequency generating device connected to the solar cell.

A portable spectroscope was used for absorption spectroscopy. The experiment was conducted in daylight on a sunny day. The receiver of the spectroscope is approximately 2 mm² circular aperture which was focused on a small area of a 125 mm c-Si solar cell. Baseline was initially obtained by analyzing the reflected light from the cell without exposure to the pulses. In the experiment, it was assumed that there is no transmission of the light through the solar cell in the spectrum of interest. The wavelengths analyzed ranged from 200 nm to 1025 nm. Pulses were then applied to the cell by connecting the source of the pulses with a cable to the front of the solar cell, which was the negative electrode. The reflected light in the same position of the receiver was analyzed. The difference in the two spectrums was calculated. The difference represents the additional absorption in the cell due to the application of pulses.

A portable spectroscope was used operating in differential emission mode to conduct photoluminescence test. The test includes subjecting the solar cell to simulated solar radiation for 30 seconds. After that, the spectroscope was used to detect the emission from the solar cell in dark condition. Total intensity is calculated by adding the individual intensities at different wavelengths. Next, the pulses were applied to the cell and test was repeated. Cumulative intensities were compared.

FIG. 15 shows a resulting l-V curve for the solar cell. The dashed curve in the figure is obtained by applying the pulses to the cell and the solid curve is the baseline curve without the pulses. From the l-V data it is observed that the short circuit current l_sc increases upon application of pulses. There is also a minor increase in open circuit voltage V_oc. This can be interpreted as increase in the number of carriers available as well as increase in the energy of the carriers upon application of the pulses. Increase in Voc implies higher energy states in the conduction band.

FIG. 16 demonstrates the generation of additional absorption peaks when the solar cell is subjected to the pulses. The observed absorption peaks support the model of FIG. 13. The data obtained is for A frequency range of 80 to 100 GHz. For higher frequencies, it expected that the absorption peaks will be lower.

The appearance of additional absorption peaks in the spectroscopic analysis demonstrates creation of new energy states upon application of the pulses. Although there are some absorption peaks at various wavelengths, a very high percentage of the absorption peaks occur at short wavelengths, between 250 nm - 300 nm, 350 nm - 400 nm, as well as other wavelengths.

FIGS. 17-19 show the photoluminescence emission from a c-Si cell before and after being subjected to the pulses. Increase in cumulative intensity implies more radiative recombination. Generally radiative recombination is from band to band transition, which in the case of silicon PV should be at approximately 1 100 nm. In the analysis, however, we discovered that a significant portion of the radiative recombination is from approximately 600 nm (2.06 eV) or approximately 900 nm (1.37 eV).

In the above experiments, it was observed that additional energy states, generally at much higher level than the bottom of the conduction band, appear and participate in the photovoltaic process. FIGS. 13 and 14 show a significantly higher than 3% increase in energy at much higher frequencies. In addition, it was observed in other experiments that a much larger increase in both open circuit voltage and short circuit current occurred under blue illumination. This demonstrates with the high frequency pulses, absorption occurs at higher energy levels. These energy states (~2 eV) do not normally exist in silicon and therefore are created. It is not believed that such effects are a result of other mechanisms.

From the absorption spectroscopy data, it can be clearly seen than additional states are created at high energy levels. This result is consistent with the findings from the l-V test. The photoluminescence data support the above conclusion too. Emissions from 2.06 eV and 1.37 states to the valence band are not possible in silicon unless those states exist.

FIG. 20 is a representation of the mechanism of power improvement from electric pulses that can arise in embodiments. FIG. 20 shows and energy band diagram, including a valence band 2042 and conduction band 2044. Additional states 2044 or 'mini bands' can be created due to the application of electric pulses of suitable frequency to the crystalline semiconductor. These states can be temporary and disappear upon the removal of pulses.

From the measurement data, we have found these additional states to be metastable with a lifetime comparable to the minority carrier life time of the solar cell (which was silicon in the experimental case). When a hot carrier is generated upon the absorption of high energy photon, the hot carriers occupy the newly generated metastable states and therefore do not thermalize in picoseconds. These carriers contribute to the energy output of the cell.

It is generally believed that capturing the energy of hot carriers would increase PV open circuit voltage and not the short circuit current. The reason for increased open circuit voltage is that hot carriers lose their energy only by dropping to the bottom of the conduction band. Since they are still in the conduction band, they are available to contribute to current. By preventing the loss of energy, the carrier's potential energy becomes available which increases the open circuit voltage.

In our experiments however, both voltage and current increases have been observed. The voltage increase can be explained by the conventional understanding of hot carriers. It is believed that current increase is possible with multi exciton generation. According to current understanding, for multi exciton generation to occur, coulombic attraction between a hot electron and a valence band hole is required. This mechanism is more likely to occur in a nanostructure due to quantum confinement. Quantum confinement enhances the coulombic interaction between electron and hole.

It is believed that the application of electric pulses of suitable frequency can cause the quantum confinement necessary for multi exciton generation. F

The photoluminescence data in FIGS. 17-19 show an increase in photoluminescence intensity on application of electric pulses. Such an effect can arise from and increase in carrier density or increase in carrier mobility. Given that the solar cell used in the experiment was a c-Si cell of good quality, the large increase in mobility which is seen in the experiments would seem not to be possible without some other effect. Therefore, it is believed that carrier density is increased through the generation of multi- excitons. While embodiments have been directed to the generation of solar power by application of electric pulses to semiconductor materials, embodiments can include utilizing the creation of additional quantum states for various other applications.

Embodiments can include tunable lasers which generate quantum states by application of electric fields, rather than conventional approaches, which can use more complex and expensive material engineering. Similarly, LEDs can utilize such effects.

Optical transmission media, can include materials to which electric pulses are applied to create additional quantum states and thereby widen the transmission bandwidth of the material, as compared to the material without the electric pulses.

Along these same lines, optical computing devices and quantum computing devices can include materials that provide additional quantum states using the approaches and effects described herein.

In the area of quantum scale semiconductor manufacturing, such as quantum wells through implant or diffusion, creation of quantum wells by application of electric fields during manufacturing could simplify the manufacturing process.

While embodiments herein have disclosed particular semiconductor materials and electric pulse generating methods and circuits, such particular embodiments should not be construed as limiting. Alternate embodiments can include different materials and/or any suitable electric pulse duration, amplitude, wave shape, etc.

It is understood that the waveform shape and periodicity shown in the various figures are representational, and should not be construed as limiting to the embodiments.

It should be appreciated that reference throughout this description to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of an invention. Therefore, it is emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various portions of this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the invention.

It is also understood that other embodiments of this invention may be practiced in the absence of an element/step not specifically disclosed herein. Further, while embodiments can disclose actions/operations in a particular order, alternate embodiments may perform such actions/operations in a different order.

Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claims require more features than are expressly recited in each claim. Rather, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Claims

IN THE CLAIMS

What is claimed is:

I . A system, comprising:

a resonant cavity formed with at least one cavity surface formed by a pyroelectric material, the resonant cavity configured to generate electrical pulses when resonating in response to receiving electromagnetic waves having at least one predetermined frequency; and

at least one photovoltaic (PV) cell coupled to receive the electrical pulses while exposed to photons.

2. The system of claim 1 , wherein the resonant cavity includes at least a first pyroelectric layer.

3. The system of claim 2, wherein the resonant cavity includes the first pyroelectric layer formed on a second waveguide layer, the second waveguide layer having a different refractive index than the first pyroelectric layer.

4. The system of claim 2, wherein the resonant cavity includes the first pyroelectric layer formed on a second pyroelectric layer, the first and second pyroelectric layer comprising different pyroelectric materials.

5. The system of claim 4, wherein the resonant cavity further includes the second pyroelectric layer formed on a third pyroelectric layer, the first and third pyroelectric layers formed from the same pyroelectric material.

6. The system of claim 1 , the pyroelectric material comprises a perovskite-type material.

7. The system of claim 1 , wherein the resonant cavity is configured to generate electric pulses of a frequency no less than 1 GHz.

8. The system of claim 1 , wherein the resonant cavity is configured to generate standing waves having a wavelength of no less than 700 nm.

9. The system of claim 1 , further including a DC bias circuit configured to apply a DC bias voltage to the resonant cavity.

10. The system of claim 1 , wherein the photovoltaic (PV) cell comprises silicon.

I I . The system of claim 10, wherein the photovoltaic (PV) cell comprises monocrystalline silicon.

12. The system of claim 1 , further including a transient suppressor unit coupled to the output of the PV cell and configured to suppress transient signals in an output current generated by the PV cell.

13. The system of claim 12, wherein the transient suppressor unit is disposed between the PV cell and an inverter unit configured to generate AC power from the output current.

14. A method, comprising:

generating electric pulses with a resonant cavity having least one cavity surface formed by at least a first pyroelectric material;

applying the pulses to a photovoltaic (PV) cell while the PV cell is exposed to photons; and

generating a PV current with the PV cell as it is exposed to the photons.

15. The method of claim 14, wherein the electric pulses have a frequency no less than 1 GHz.

16. The method of claim 15, further including generating standing waves in the resonant cavity having a wavelength of no less than 700 nm.

17. The method of claim 14, wherein the resonant cavity comprises at least two layers stacked on top of one another, a first layer comprising the first pyroelectric material, the second layer comprising a material having a different refractive index than the first material.

18. The method of claim 14, wherein the resonant cavity comprises at least two layers stacked on top of one another, a first layer form of the first pyroelectric material, the second layer formed of a second pyroelectric material different than the first pyroelectric material.

19. The method of claim 14, wherein:

applying the electric pulses to the PV cell generates additional photo absorption states in the PV cell as compared to the PV cell without the application of the electric pulses; and

generating the PV current includes an additional PV current component corresponding to the additional absorption state as compared to the PV cell without the application of the electric pulses.

20. The method of claim 14, further including applying a DC bias to the PV cell.