WO2013137708A1

WO2013137708A1 - Wide acceptance angle solar cell device

Info

Publication number: WO2013137708A1
Application number: PCT/MY2012/000051
Authority: WO
Inventors: Witjaksono Gunawan
Original assignee: Mimos Bhd
Current assignee: Mimos Bhd
Priority date: 2012-03-13
Filing date: 2012-03-13
Publication date: 2013-09-19
Anticipated expiration: 2014-09-13

Description

WIDE ACCEPTANCE ANGLE SOLAR CELL DEVICE

TECHNICAL FIELD The present invention relates to the improvement on fabrication of solar cell and more particularly related to a wide acceptance angle of solar cell device.

BACKGROUND ART

Ideally, solar cell should be able to capture all light emitted from the sun during daytime, meaning that the light absorption by the solar cell should not be dependence of the position of the sun at given surface area of the solar cell. During dawn to dusk, the incidence angles of light hitting the planar surface of the solar cell from the sun keeps changing, hence, the light absorption is also affected. The effectiveness of incident light depends on a factor of sin ( ) , where a is the angle of the light incidence to the normal axis of the solar cell.

Main issues relating to the use of solar cell are variation of sunlight angle to the solar cell during daytime results in low and variant efficiency of the solar cell. Another problem is addition of mechanical tracking equipment and/or mirrors and lenses result in complexity of the solar system and the same time making the solar system bulkier and heavier. Furthermore, brittleness of the substrate makes it hard to implement on the micro devices, i.e. sensor motes. The fixed position of the solar cell (on the micro devices) makes it difficult to implement on real application.

In example of prior arts, some geometrical structuring has been implemented to increase the number of the reflected light so the light is eventually hitting the substrate/active region. US Patent 5,080,725 and US 2007/0062575 Al used the surface structuring in the form of geometrical ridges and pyramids and fine structuring to form irregularities on the surface, respectively, causing an increased number of passes of trapped light within the cell, however the light within the geometric structure are not guided and geometrical structuring with ridges, pyramids, and fine irregularities do not effective solve the sin (a) problem because the light is not being trapped within the cell structure.

Other approach by different prior art was using nano- structured at horizontal surface to capture the absorbed light. US Patent 7,655,860 proposed the solar cell, which has a substrate having a horizontal surface, and an electrode layer on the surface. The electrode has a plurality of vertical surfaces substantially perpendicular to the horizontal surfaces, and light harvesting rods are coupled to the vertical surface of the electrode. This approach successfully guide the light inside the cell and allow them to hit the active region, however, it does not solve the sin (a) problem. The planar structure will not be effective coupling the light when the sun position changes.

The need for continuous and sustainable energy source to supply electrical power for micro devices has been increasingly important because of the short lifetime of batteries. Applications that require many micro-device deployments, such as sensors in wireless sensor network (WSN) definitely require continuous and sustainable energy sources to lengthen the lifetime of their electronic devices. Many choices of energy harvesting have been readily available and solar cell becomes the main candidate for this purpose because it theoretically provides high power density and easy manufacturing. However, for real deployment on micro devices, some issues hinder its potential, such as high dependence of sun position, brittleness of the substrates and rigid or fixed cell installation.

The proposed invention is to increase the light coupling and the same time guide the light within the cell to hit the active region effectively. The light coupling is increased by capturing all incident lights at any position of the sun during the daytime. This proposed invention is to solve the sin (a) problem. Later the light that is coupled into the cell will be guided further through the tapered walls and direct it to the active region so eliminate loss of light within the cell.

DISCLOSURE OF THE INVENTION

The present invention aims to provide to the improvement of fabrication of solar cell which more particularly to a wide acceptance angle of solar cell device.

In a preferred embodiment of the present invention, a wide acceptance angle solar cell device comprising a substrate of active material with a energy coupling layer on the top, which is geometrically structured with nano- structures with the outer surfaces having their normal axis perpendicular to the tangential axis of the substrate and is, at least, symmetrically curved.

In another preferred embodiment of the present invention, the substrate of active material is flexible and/or solid material.

In another preferred embodiment of the present invention, the substrate of active material is curved or flat substrate .

In another preferred embodiment of the present invention, the energy coupling layer is patterned with nano structure.

In another preferred embodiment of the present invention, the nano structure baseline structurally follows the shape of the said substrate of active material.

In another preferred embodiment of the present invention, the nano structure is geometrically texture of, at least, tubes or wires to guide the light to the active region . In another preferred embodiment of the present invention, the nano tubes having tapered wall to enhance the guiding mechanism.

In another preferred embodiment of the present invention, the nano tubes of flat substrate having the top surface facing upward with an angle while the nano tube baseline is horizontally flat.

In another preferred embodiment of the present invention, the energy coupling layer is anti reflecting material.

In another preferred embodiment of the present invention, a method of fabricating a solar cell with flexible substrate comprising the steps of patterning top energy coupling layer by, but not limited to, lithography process, with regular shapes, using selective etching to etch a energy coupling layer thereby producing geometric structure of, at least, tubes or wires, and curving the flexible substrate after completed the process by an angle. In another preferred embodiment of the present invention, the curve angles are in the range of 2° - 45°.

The present invention consists of features and a combination of parts hereinafter fully described and illustrated in the accompanying drawings, it is being understood that various changes in the details may be made without departing from the scope of the invention or sacrificing any of the advantages of the present invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

To further clarify various aspects of some embodiments of the present invention, a more particular description of the invention will be rendered by references to specific embodiments thereof, which are illustrated, in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the accompanying drawings in which: FIG. 1 describes the sun light incident into the solar cell and the sun movement during dawn to dusk.

Fig. 2 illustrates basic structure of wide-angle acceptance solar cell.

Fig. 3 shows portion of light that is

transmitted and reflected after incident to the

interface layer. Fig. 4 shows the mechanism of total internal reflection.

Fig. 5 describes the path of light on the incident, escaped and guided light. Fig 6 shows (a) acceptance angle of light incident of geometrical structure on the coating layer to ensure total internal reflection; and (b) curved substrate to widen the acceptance angle. Fig 7 describes the curved substrate with geometrical structures of the coating layer with their top surface normal axis perpendicular to the tangential of the substrate below it. DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

According to FIG.l, the efficiency of solar cells (13) depends on the electrical power it generates out as percentage of the power in incident sunlight (11) . One of the most fundamental limitations on the efficiency of a solar cell (13) is light or energy capturing due to the position of sun (10), light reflection (12) and light guidance, to the active region. When the light (11) is hitting the surface of the solar cell (13), a fraction of the light is reflected (12) and the rest of the light that is transmitted could be diverted out and not reaching the active region. Only light (13) that hitting the active layer will potentially produce the electron for energy generation. Other important aspect in efficiency of solar cell (13) is its location with respect to the solar cell (13) . As the sun (10) moving from dawn to dust, the effective light (11) hitting the solar cell (13) also changing. This effective light incident follows sin a equation and it will be referred here as sin a problem. Now referring to FIG. 2, the invention aims to solve the sin a problem using geometric structuring solar cell on the top/coating surface (111) , in the form of tapered side walls of the (nano) tubes (110), and are formed at angle such that the incident light top surface could be either curved or normal to the substrate. Such curved surface (111) and tapered (nano) tubes (110) result in increased light absorption at all angles of the light source and effectively guide the light inside the tapered tubes by internal reflection thereby increasing the light being absorbed .

The coating layer (211) is antireflective material to allow the incident light to transmit to the next layer without any reflection. Fig. 3 shows the mechanism how light is transmitted and reflected when the photon hitting the coating layers (211) through air (210) and the following show Equation 1, 2, and 3.

2ncoatingd cos θ₂ — ταλ

[3] The reflection would be minimized by inserting the immediate layer as given by equation [2] and thickness following equation [3].

The light can be converted efficiently as long as all the light in the coating layer can be guided to the active region. The guiding mechanism can be served using total internal reflection from the glass region (311) to the air region (310) as shown in Figure 4.

Total internal reflection occurs when no light is escaped from the coating layer. Fig. 5 shows complete light paths of light from incident (410) to guided light (412) and also includes the escaped light (411). According to Snell's law only certain incident angles could have no escaped light (411).

Referring to FIG.6a and 6b, in accordance with one embodiment of the invention, a solar cell device may comprise a coating layer with a structure (510) to capture and guide the incident energy from a photon source when the light impinges the top surface and channel that photon into the active region. Furthermore the solar cell device may have curve baseline surface (511), in order to enhance the acceptance angle of the incident energy from a photon source regardless of the position of that source.

Referring to FIG.7, in accordance to another embodiment, the solar cell device may comprises a geometric structure of the coating, i.e. nano tubes (670) in such a way that the surface of the geometrical structure (610) facing outward parallel to a normal axis (620) to its substrate below it. The said normal axis (620) is always perpendicular to tangential axis (630) of the curved substrate surface (650). Said curved substrate (650) has an angle such a way that it can optimize the acceptance angle of the light incident into the substrate. By determining the refractive index of the coating layer and the requirement of total internal reflection, the angle of the curved substrate, β, can be determined in order to have full acceptance angle on any position of the sun during dawn to dusk. The substrate and the active layer (660) of the solar cell device is flexible substrate which can be bended to meet the full acceptance angle.

Referring now to FIG.8, in accordance with yet another embodiment of the invention, the geometrical structure could have a flat substrate with oriented top surface of the geometrical structure. The top layer of the solar cell device is the geometrical structure (710) , with its top surface, (720), oriented outward to allow widen angle acceptance of incident light. The angles of outward-facing surfaces of each said geometrical structures are determined by the number of the said geometrical structure, the cell surface and the cumulative angle, β. The cumulative angle gives full angle acceptance of incident light on the solar cell. This geometrical structure is having the top surface wider than the bottom surface to better receiving and guiding the photons, which have been coupled to the structure, and direct it to the active region to effectively trigger the creation of electrons. Each of the geometrical structure accepts some range of incident angles before it guides the photon by total internal reflection and the cumulative angle ensures full acceptance angle. In accordance with yet another embodiment, the geometrical structures may be design to have sloped walls (740) thus enhancing further the photon trapping mechanism with solid structure (750). In accordance with yet another embodiment, the geometrical structure may further comprise nano tube structure or nano pillars with narrower base and, in addition, the tubes or nano pillars may include support layer to protect the structural shape of the geometrical structures .

In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art will appreciate that various modifications and changes can be made without departing from the scope of the present invention as set forth in the various embodiments discussed above and the claims that follow. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element (s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements as described herein.

Claims

1. A wide acceptance angle solar cell device (200) comprising : a substrate (111) of active material with a energy coupling layer on the top, which is geometrically structured with nano-structures (110) with the outer surfaces having their normal axis perpendicular to the tangential axis of the substrate (111) and is, at least, symmetrically curved.

2. The solar cell (200) as claimed 1, wherein the substrate (111) of active material is flexible and/or solid material.

3. The solar cell (200) as according to claim 2, wherein the substrate (111) of active material is curved or flat substrate.

4. The solar cell as according to claim 1, wherein the energy coupling layer is patterned with nano structure (110) .

5. The solar cell (200) as according to claim 4, wherein the nano structure (110) baseline structurally follows the shape of the substrate (111) of active material.

The solar cell (200) as according to claim 4, wherein the nano structure (110) is geometrically texture of, at least, tubes or wires to guide the light to the active region.

The solar cell (200) as according to claim 6, wherein the nano structure (110) having tapered wall to enhance the guiding mechanism.

The solar cell (200) as according to claim 6, wherein the nano tubes (110) of flat substrate having the top surface facing upward with an angle while the nano tube baseline is horizontally flat.

9. The solar cell (200) as according to claim 1, wherein the energy coupling layer is anti reflecting material.

10. A method of fabricating a solar cell with flexible substrate comprising the steps of:

patterning top energy coupling layer by, but not limited to, lithography process, with regular shapes .

using selective etching to etch a energy coupling layer thereby producing geometric structure of, at least, tubes or wires, curving the flexible substrate after completed the process by an angle.

11. The method as according to claim 10 wherein the curve angles is in the range of 2° - 45°.