Thermally insulating and transparent stacked organic solar cells

Abstract

An exemplary transparent stacked organic solar cell comprises a transparent substrate; a first transparent electrode disposed on a surface of the transparent substrate; and a series of interconnected organic active layers disposed on a surface of the first transparent electrode. The series of interconnected organic active layers comprises at least a front subcell that blocks ultraviolet wavelengths from passing through the front subcell; and a rear subcell that blocks infrared wavelengths from passing through the rear subcell. The solar cell further comprises a distributed Bragg reflector disposed on a surface of the rear subcell, wherein the distributed Bragg reflector reflects unblocked infrared photons at an interface between the rear subcell and the distributed Bragg reflector. Additionally, the series of interconnected organic active layers is configured to allow visible light wavelengths to pass through the transparent stacked organic solar cell, wherein the transparent stacked organic solar cell is fully transparent.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to co-pending U.S. Provisional Application No. 62 / 853,978, filed May 29, 2019, and entitled “Heat Insulating Transparent Tandem Organic Solar Cells,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates generally to solar cell technology. Background Art

[0004] For the widespread development of photovoltaics, it is crucial to develop solar cells that are affordable for integration into standard products and systems. Organic solar cells (OSCs) are considered a promising technology because they have many attractive advantages, such as low cost, fast energy payback time, low weight, flexibility, and most importantly, transparency. Such transparent solar cells (TSCs) have attracted widespread attention due to their potential for integration into building facades, roofs, solar windows, automotive windshields, and self-powered electronic devices. The potential market size has grown dramatically in recent years.

[0005] Conventional crystalline silicon TSCs work by diffusing sunlight through the uncovered portion of the panel (which does not contain opaque solar cells), while organic TSCs use nearly transparent electrodes and ultra-thin light-absorbing materials that provide good transparency throughout the panel. As a result, organic TSCs offer a much wider range of colors and brightness than conventional TSCs. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Many aspects of the present disclosure may be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, but emphasis is placed on clearly illustrating the principles of the present disclosure. Additionally, in the drawings, like reference numerals denote corresponding components throughout the various views.

[0007] Figure 1 is a schematic diagram of an exemplary embodiment of a heat-insulating and transparent stacked organic solar cell according to the present disclosure.

[0008] Figure 2 is a diagram showing the solar spectral irradiance and the corresponding energy fraction at different wavelengths of light.

[0009] Figure 3 is an exemplary illustration of a diffractive Bragg reflector according to an embodiment of the present disclosure.

[0010] Figure 4A Schematic diagram of a photoactive layer fabricated on a quasi-periodic polycrystal nanopatterned (QPN) substrate according to various embodiments of the present disclosure.

[0011] Figure 4B Schematic diagrams illustrating polycrystalline nanopatterns having various pitch sizes according to various embodiments of the present disclosure.

[0012] Figure 4C is a graph showing predicted enhancement of sunlight capture at different wavelengths according to various embodiments of the present disclosure.

[0013] Figure 4D is a scanning electron microscope image of an exemplary QPN according to various embodiments of the present disclosure. Summary of the Invention

[0014] Aspects of the present disclosure relate to transparent stacked organic solar cells. In one aspect, wherein the transparent stacked organic solar cell comprises a transparent substrate; a first transparent electrode disposed on a surface of the transparent substrate; and a series of interconnected organic active layers disposed on a surface of the first transparent electrode. The series of organic interconnected active layers comprises at least a front subcell that blocks ultraviolet wavelengths from passing through the front subcell; and a rear subcell that blocks infrared wavelengths from passing through the rear subcell. Additionally, the transparent stacked organic solar cell comprises a distributed Bragg reflector disposed on a surface of the rear subcell, wherein the distributed Bragg reflector reflects unblocked infrared photons at an interface between the rear subcell and the distributed Bragg reflector. Furthermore, the series of interconnected organic active layers is configured to allow visible light wavelengths to pass through the transparent stacked organic solar cell, wherein the transparent stacked organic solar cell is fully transparent.

[0015] Aspects of the present disclosure also relate to a method for realizing a transparent tandem organic solar cell. The method includes: providing a first transparent electrode, the first transparent electrode being provided on a surface of a transparent substrate; providing a series of interconnected organic active layers on the surface of the first transparent electrode; configuring the series of interconnected organic active layers to allow visible wavelengths to pass through the series of interconnected organic active layers, wherein the series of interconnected organic active layers includes at least a front subcell that blocks ultraviolet wavelengths from passing through the front subcell; and a rear subcell that blocks infrared wavelengths from passing through the rear subcell; providing a mirror on the surface of the rear subcell to form the transparent tandem organic solar cell; and reflecting unblocked infrared photons at an interface between the rear subcell and the mirror; wherein the transparent tandem organic solar cell is fully transparent.

[0016] In one or more aspects, the transparent tandem organic solar cell can be in the form of a film applied to a window of a structure. In one or more aspects, the structure can include a building or a vehicle. In one or more aspects, the transparent tandem organic solar cell can be integrated into a building facade, roof, or automobile windshield.

[0017] In one or more aspects, a distributed Bragg reflector configured to block thermal energy from being provided through a transparent stacked organic solar cell and / or may include a periodic array of lithium fluoride (LiF) and molybdenum oxide (MoOx) layers.

[0018] In one or more aspects, the series of interconnected organic active layers is configured to convert blocked wavelengths of light into electricity and / or includes at least one antireflective coating.

[0019] In one or more aspects, the transparent tandem organic solar cell can be embedded in a window, integrated into a building facade or roof, and / or can be in the form of a film of photovoltaic material. In one or more aspects, the transparent tandem organic solar cell can be a quasi-periodic polycrystalline nanopatterned structure with different pitch sizes coupled to the top or bottom of the transparent tandem organic solar cell. DETAILED DESCRIPTION

[0020] The present disclosure describes an embodiment of a high-performance transparent stacked organic solar cell that can be used for both power generation and heat insulation. In one such embodiment, the transparent solar cell is configured to fully utilize the ultraviolet (UV) and infrared (IR) regions of the spectrum by using or stacking a series of solar cells while maintaining high transparency. The series of solar cells can absorb specific invisible wavelengths of light (e.g., ultraviolet and infrared) and convert them into electricity while allowing transmission of visible wavelengths of light. In addition, as a non-limiting example, a mirror device (e.g., a distributed Bragg reflector (DBR)) can be used to reflect infrared wavelengths of light so that they cannot be transmitted through the solar cell, thereby preventing heat energy from being provided to the interior of the building by infrared light. Therefore, by blocking IR light with DBR, the embodiment of the exemplary transparent solar cell gives the transparent solar cell enhanced heat insulation performance, which opens up new applications for organic transparent solar cells. As an illustration, these heat insulation properties can be used to control room temperature according to the way photovoltaic material films are applied to windows of buildings or vehicles, which can significantly reduce the overall lighting, heating and cooling costs of buildings. Other applications include integrating them into building facades, roofs, solar windows, car windshields and self-powered electronic devices.

[0021] Referring now to the accompanying drawings, Figure 1The structure of a heat-insulating, transparent, stacked organic solar cell according to an embodiment of the present disclosure is shown. In this example, the solar cell is divided into three layers: (1) a front organic sub-cell that absorbs and blocks ultraviolet and short-wavelength photons, including a portion of the visible spectrum adjacent to the ultraviolet spectrum; (2) a rear organic sub-cell that absorbs long-wavelength and infrared photons, including a portion of the visible spectrum adjacent to the infrared spectrum; and (3) a distributed Bragg reflector (DBR) that reflects unabsorbed infrared photons at the interface between the rear cell and the reflector, thereby blocking heat sources from penetrating the reflector. In various embodiments, the solar cell can be in the form of a thin film, which can be applied to a transparent structure, such as a window, or a non-transparent structure.

[0022] Because organic solar cells are susceptible to thermal losses, especially for devices using low-bandgap semiconductors, stacking individual cells (also called subcells) with complementary absorption characteristics in series is an effective way to address the limitations of single-junction solar cells. Due to the series-connected subcells, such tandem solar cells enjoy significantly higher voltage output. Previous tests have observed that the power conversion efficiency (PCE) of tandem TSCs is approximately 50% better than that of single solar cells, due at least to the reflection of incident light, which doubles the optical path in the tandem transparent solar cell and increases light absorption.

[0023] Thus, according to the present disclosure, by using a multilayer configuration of interconnect layers (by electrically connecting the subcells and the transparent top electrode), an exemplary TSC can be fabricated that is well sensitized in different regions of the infrared (IR) and / or ultraviolet (UV) spectrum and minimizes optical absorption in the visible spectrum. Thus, in various embodiments, the interconnect layers may be composed of an antireflective coating, a transparent substrate, a transparent electrode, multiple active layers, a transparent electrode, a diffractive Bragg reflector, and / or an antireflective coating.

[0024] According to various embodiments, exemplary thermally insulating and transparent stacked organic solar cells are designed to have good transmittance in the visible light range (400-700 nm). Generally, the transparency of a TSC can be determined by the average visible light transmittance (AVT), where this value represents the average percentage of light transmitted by the solar cell in the visible wavelength range (400-700 nm) based on the spectrally dependent response of the human eye. A minimum value of AVT = 25% is generally recommended for window applications in industry.

[0025] Therefore, if Figure 1As shown, for the layers (1) and (2) (i.e., the front organic subcell and the back organic subcell, respectively) of the exemplary embodiment of the thermally insulating transparent stacked organic solar cell, the light absorption requirements are met by selecting organic materials with appropriate band gaps. For example, for an ideal TSC, it is preferred that ultraviolet (UV) and infrared (IR) or near infrared (NIR) wavelengths are absorbed while maintaining high transmittance in the visible range, because according to the energy distribution of the standard AM 1.5G solar spectrum, more than half of the solar energy is distributed in the NIR region (e.g., Figure 2 shown).

[0026] To enhance photon collection within thermally insulating and transparent stacked organic solar cells, in various embodiments, a photonic crystal structure, such as a distributed Bragg reflector (DBR), can be placed on top of a transparent electrode. Exemplary DBRs consist of a periodic array of low- and high-refractive-index layers, allowing light to be partially refracted, reflected, and transmitted at various interfaces. The DBR's lattice spacing and layer refractive indices determine whether the interference between reflected or transmitted light beams at a specific wavelength is constructive or destructive.

[0027] Next reference Figure 3 , which shows a 1D photonic crystal array comprising a periodic array of lithium fluoride (LiF) and molybdenum oxide (MoOx) layers that, for various embodiments, can serve as a good reflector in the IR region of the spectrum. In particular, this 1D photonic crystal array selectively reflects a major portion of IR light while maintaining high visible light transmittance. During fabrication, this exemplary DBR can be deposited by thermal evaporation or low-temperature solution processing, which does not cause degradation to the underlying solar cell.

[0028] In addition to or instead of planar DBR, quasi-periodic polycrystalline nanopatterns (QPNs) can be applied on the top or bottom of the exemplary solar cell to enhance light absorption of selective wavelengths. However, conventionally, a solar tracker is required to rotate the solar panel to maintain vertical incidence (of the sun) to achieve high efficiency, thereby increasing the installation cost, and the maintenance cost for solar tracking consumes unnecessary energy to rotate the solar panel. Differently, the main concept of QPN is to perform light harvesting through a light scattering mechanism (for capturing sunlight). As shown in Figures 4A-4D As demonstrated in

[15] , quasi-periodic polycrystalline nanopatterns (QPNs) advantageously couple a wide band of the solar spectrum from a wide solid angle range with high integrated photocurrent compared to periodic single-crystalline nanopatterns. Here, Figure 4A is a schematic diagram of a photoactive layer fabricated on a QPN substrate according to various embodiments of the present disclosure; Figure 4Bis a schematic diagram illustrating polycrystalline nanopatterns having various pitch sizes according to various embodiments of the present disclosure; Figure 4C is a graph showing the different wavelengths (at different wavelengths) according to various embodiments of the present disclosure. Figures 4A-4C a plot of the predicted enhancement in sunlight capture at Δ denoted in FIG; and Figure 4D is a scanning electron microscope image of an exemplary QPN according to various embodiments of the present disclosure.

[0029] In summary, the embodiments of the present disclosure provide a high-performance transparent stacked organic solar cell that can be used for both power generation and heat insulation. By appropriately configuring subcells that fully utilize the UV and IR regions while maintaining high transparency, a high-performance transparent solar cell can be achieved. In addition, by using a DBR that effectively blocks IR light, a transparent solar cell with enhanced heat insulation performance can also be achieved, which has the following properties: (1) an organic TSC with a power conversion efficiency greater than 15%; (2) a high average visible light transmittance with a minimum value of 30%; (3) 85% or higher infrared radiation suppression; and (4) a high open circuit voltage (>2.5V) with a stacked structure; etc. In addition to the DBR, in certain embodiments of the high-performance transparent stacked organic solar cell, a QPN is integrated on the top or bottom of the solar cell, wherein the QPN is configured to couple a broadband from the solar spectrum over a wide solid angle range with a high integrated photocurrent.

[0030] It should be emphasized that the above-described embodiments of the present disclosure are merely examples of possible implementations and are set forth solely for the purpose of providing a clear understanding of the principles of the present disclosure. Numerous variations and modifications may be made to the above-described embodiments without departing substantially from the principles of the present disclosure. All such modifications and variations are intended to be included within the scope of the present disclosure and protected by the appended claims.

Claims

1. A transparent stacked organic solar cell, comprising: Transparent substrate; A first transparent electrode is provided on the surface of the transparent substrate; a series of interconnected organic active layers disposed on a surface of the first transparent electrode, wherein the series of interconnected organic active layers includes at least a front subcell that blocks ultraviolet wavelengths from passing through the front subcell; and a rear sub-cell that blocks infrared wavelengths from passing through the rear sub-cell; as well as a distributed Bragg reflector disposed on a surface of the rear subcell, wherein the distributed Bragg reflector reflects unblocked infrared photons at an interface between the rear subcell and the distributed Bragg reflector; wherein the series of interconnected organic active layers is configured to allow visible light wavelengths to pass through the transparent stacked organic solar cell; The transparent stacked organic solar cell further includes a quasi-periodic polycrystalline nano-pattern structure with different width sizes, which is located on the front sub-cell or on the distributed Bragg reflector disposed on the surface of the rear sub-cell.

2. The solar cell of claim 1, wherein the distributed Bragg reflector comprises a periodic array of lithium fluoride (LiF) and molybdenum oxide (MoOx) layers. 3 . The solar cell according to claim 1 , wherein the distributed Bragg reflector is configured to block heat energy from being provided through the transparent stacked organic solar cell. The solar cell according to claim 1 , wherein the transparent stacked organic solar cell is embedded in a window. The solar cell according to claim 1 , wherein the transparent stacked organic solar cell is in the form of a photovoltaic material film.

6. The solar cell of claim 1, wherein the series of interconnected organic active layers further comprises at least one antireflective coating.

7. The solar cell of claim 1, wherein the series of interconnected organic active layers is configured to convert light of a blocked wavelength into electricity.

8. The solar cell according to claim 1, wherein the transparent tandem organic solar cell is integrated into a building facade or roof.

9. A method for realizing a transparent stacked organic solar cell, comprising: Providing a first transparent electrode, wherein the first transparent electrode is provided on the surface of the transparent substrate; providing a series of interconnected organic active layers on the surface of the first transparent electrode; configuring the series of interconnected organic active layers to allow visible wavelengths to pass through the series of interconnected organic active layers, wherein the series of interconnected organic active layers includes at least a front subcell that blocks ultraviolet wavelengths from passing through the front subcell and a rear subcell that blocks infrared wavelengths from passing through the rear subcell; Disposing a reflective mirror on the surface of the rear sub-cell to form the transparent stacked organic solar cell; coupling quasi-periodic polycrystalline nano-pattern structures having different width sizes, wherein the quasi-periodic polycrystalline nano-pattern structures are located on the front sub-cell or on the reflective mirror disposed on the surface of the rear sub-cell; as well as Unblocked infrared photons are reflected at the interface between the rear subcell and the mirror.

10. The method of claim 9, wherein the reflector comprises a distributed Bragg reflector.

11. The method of claim 10, wherein the distributed Bragg reflector comprises a periodic array of lithium fluoride (LiF) and molybdenum oxide (MoOx) layers.

12. The method of claim 9, further comprising applying the transparent stacked organic solar cell in film form to a window of a structure.

13. The method of claim 12, wherein the structure comprises a building.

14. The method of claim 12, wherein the structure comprises a vehicle.

15. The method of claim 9, wherein the series of interconnected organic active layers further comprises at least one antireflective coating.

16. The method of claim 9, further comprising converting light of the blocked wavelength into electricity.

17. The method according to claim 9, further comprising integrating the transparent stacked organic solar cell into a building facade or roof.

18. The method of claim 9, further comprising integrating the transparent stacked organic solar cell into an automobile windshield.

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