WO2012102603A1

WO2012102603A1 - Multiple scan single pass line scan apparatus for solar cell inspection and methodology thereof

Info

Publication number: WO2012102603A1
Application number: PCT/MY2012/000006
Authority: WO
Inventors: Yang Yi FOO; Koon Yin GOON; Soo Yi KOAY; Cowei OOI
Original assignee: Tt Vision Technologies Sdn Bhd
Priority date: 2011-01-28
Filing date: 2012-01-20
Publication date: 2012-08-02
Also published as: MY159053A

Abstract

The present invention relates generally to a multiple scan single pass line scan apparatus for solar cell inspection, comprising at least one line scan imaging device, at least one beam splitter, at least one light beam illuminated from an illumination source and a pair of equilateral triangular prism to obtain the various defects information of the solar cell.

Description

MULTIPLE SCAN SINGLE PASS LINE SCAN APPARATUS FOR SOLAR CELL INSPECTION AND METHODOLOGY THEREOF

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to a multiple scan single pass line scan apparatus for solar cell inspection, comprising at least one line scan imaging device, at least one beam splitter, at least one light beam illuminated from an illumination source and a pair of equilateral triangular prism to obtain the various defects information of the solar cell. 2. BACKGROUND OF THE INVENTION

Due to the present concern over rapidly increasing cost of conventional energy forms and environmental reasons, countries all over the world are dedicated to the development of solar energy. Solar cell (also called photovoltaic cell) is a semiconductor component that converts the energy of solar light into electric energy by the photovoltaic effect. Assemblies of solar cells are used to make solar modules (also known as solar panels). The energy generated from the solar modules are referred to as solar power, which is an example of solar energy.

The performance of a solar cell is mainly determined by the conversion efficiency between light and electricity. Among the solar cell products on the market today, solar cells made by silicon have the greatest market share. Categorizing by crystal structure, they can be divided into single-crystal silicon solar cell, poly-crystalline silicon solar cell and amorphous silicon solar cell. Finding ways to raise the energy conversion efficiency and lowering the thickness of silicon wafers is another major focus in the development of solar cell technology.

During the manufacturing of solar cell, inspection may need to be performed routinely to ensure that defective unit of solar cell are identified so as to control the quality of the solar cells. Generally, defects may happen on a solar cell in a few ways such as print electrode defects, surface passivation defects, ARC (Anti-reflective coating) color defects, cell geometric variations, cell edge defects and etc. In addition, due to the increasing requirements to reduce the thickness of the solar silicon and to increase the size of solar cell so that manufacturing cost can be reduced and at the same time raise energy conversion efficiency. However, this will increase the tendency of solar cell mechanical structure to be weaken and hence leading to warping or deformation.

In order to improve the quality of the solar cell, solar cell manufacturers need to characterize the quality of solar cell on multiple process gates of solar cell production line as well as to separate the defective units from the working units. In view of the above requirements, it is paramount important to have a vision inspection system and method, whereby solar cell is illuminated with lights to detect the existence and location of defects on a solar cell, and hence to sort the cells with defects into different quality classes.

Generally line scanning method is used in solar cell vision inspection system, due to its ability to produce high resolution image at high speed. A line scan camera is normally coupled with single or multiple line lights to produce a single frame image or web images. This is normally used in printing industry where inspection is progressing continuously. Conventional method of line scan optical setup consists of the camera and line light which is set at an angle relative to each other, as shown in FIG. 1. Normally either a monochromatic color or white light is used, depending on type of application. White line light is used especially when color line scan camera is used to illuminate multi-spectral features on the solar cell. Otherwise specific color spectrum, i.e. red, green and blue will be used as light source when coupled with monochrome line scan camera. And depending on the angle in between, the setup affects the quality of the image acquired.

Conventionally, AOI (Automated Optical Inspection) system of solar cell using line light is adopted and it works fine for solar cell which is perfectly flat. However this method has a problem when dealing with warped solar cell, when the reflection and refraction of the light are no longer consistent, it changes according to cell warping surface, and thus the amount of lights received by camera vary from beginning to the end of the cell scanning (FIG. 2). An even and high contrast image is difficult to be obtained, unless the camera or the line light is able to dynamically oriented according to the angle of the cell warping surface to receive maximum reflection. FIG. 3 illustrates the reflected light angle is identical to the angle of incident light when it is projected on flat surface and the amounts of refractions is depends on surface property and smoothness. FIG. 4 illustrates the normal line shifted to different angle due to the curvature profile of a warped surface, and the angle and direction of the incident and reflected light will change along the warp surface when solar cell moves along the scanning line.

FIG. 5 shows another prior art by using two or multiple line lights which are mounted at the same angle on both side of the camera and the camera is mounted vertically and perpendicular to solar cell surface to increase the amount of light illuminated at certain line of the solar cell surface. However, the same problem may still exists due to the light reflection, which is not completely reflected back to the camera as the amount and direction of reflected lights is depend on the curvature surface of the warped solar cell. Moreover, the various prior arts are using monochromatic or polychromatic camera coupled with white line lights to generate single spectral image which is in most cases of solar cell inspection, single spectral image will not able to discern various chromatic defects accurately when their color hue, saturation or intensity (HSI values) values are overlapping with one another. In addition, the method of acquiring multiple color planes of solar cell is using multiple optical setups, each with different light spectrum illumination. This will require more space, more illumination and camera that lead to bigger footprint and higher setup cost.

It would hence be extremely advantageous if the above shortcoming is alleviated by having a multiple scan single pass line scan optical apparatus, comprising a plurality of co-linear line lights with different spectral frequency and a plurality of receiver sensor cameras to generate multi-spectral undistorted and highly even across the entire field of view solar cell images for solar cell inspection. By adopting the present invention using polychromatic white line light with a multi-sensor camera, multiple colour planes image can be obtained by having one optical setup.

3. SUMMARY OF THE INVENTION

Accordingly, it is the primary aim of the present invention to provide a multiple scan single pass line scan optical apparatus for solar cell inspection to reduce setup cost and improve inspection yield.

It is yet another object of the present invention to provide a multiple scan single pass line scan optical apparatus wherein multiple optical setups is not required and hence the required setup space is reduced.

It is yet another object of the present invention to provide a multiple scan single pass line scan optical apparatus whereby multi- spectral co-linear lights are illuminated to solar cell and reflected co- linear multi-spectral lights are detected by multi-receivers sensors or cameras to obtain various defects information of the solar cell without being affected by the warped cell surface.

It is yet another object of the present invention to provide a multiple scan single pass line scan optical apparatus to separate defective units from working units.

It is yet another object of the present invention to provide a multiple scan single pass line scan optical apparatus wherein image contrast is increased and higher spatial resolution is obtained as more lights are reflected back to the camera. It is yet another object of the present invention to provide a multiple scan single pass line scan optical apparatus wherein the obtained image evenness is improved.

It is yet another object of the present invention to provide a multiple scan single pass line scan optical apparatus wherein intended colour components to be used are focused to reduce interference from adjacent colour spectrum.

Other and further objects of the invention will become apparent with an understanding of the following detailed description of the invention or upon employment of the invention in practice.

These and other objects are achieved by the present invention, which in its preferred embodiment provides,

A multi scan single pass line scan apparatus for solar cell inspection comprising: at least one line scan imaging device (601); at least one light beam (605) having a plurality of wavelengths illuminated from an illumination source (607); characterized in that said apparatus further comprising of at least one beam splitter (603) to direct said illuminated light beam (605) to be projected substantially perpendicular onto a solar cell surface and said light beam is reflected almost at the same angle of said projected light and reach the said line scan imaging device (601).

In a second embodiment, it provides:

A methodology of multi scan single pass line scan for solar cell inspection comprising steps of: i. projecting a light beam (605) from an illumination source (607) towards a solar cell surface; ii. providing at least one line scan imaging device (601) to detect the reflected light from said solar cell surface; iii. acquiring images from said line scan imaging device (601); characterized in that said methodology further comprises of following steps before said reflected light is detected by said line scan imaging device: i. said light beam (605) having a plurality of wavelengths from an illumination source (607) strikes the first equilateral prism (903) and disperse to break light into individual spectral component; ii. said dispersed multi-spectral component lights strike the second equilateral prism (904) at an angle substantially equivalent to the exit angle from the first equilateral prism (903) in order for said component lights to be diffracted and transmitted as substantially parallel beams going out from said second equilateral prism; iii. said illuminated light beams passing through at least one colour filter and at least one focusing lens to filter out unwanted colour spectrums and at the same time to focus the intended colour component lights before said substantially parallel beams strikes the said beam splitter (603); iv. said substantially parallel multi-spectral component lights strike the beam-splitter (603) to generate a co- linear multi-spectral lights towards said solar cell surface; v. the intended colour component lights are reflected (908) and transmitted to the multi spectral sensor imaging device.

In a third embodiment, it provides:

A methodology of multi scan single pass line scan for solar cell inspection comprising steps of: i. projecting a light beam (605) from an illumination source (607) towards a solar cell surface; ii. providing at least one line scan imaging device (601) to detect the reflected light from said solar cell surface; iii. acquiring images from said line scan imaging device (601); characterized in that said methodology further comprises of following steps before said reflected light is detected by said line scan imaging device: i. said light beam (605) having a plurality of wavelengths from an illumination source (607) strikes the first equilateral prism (903) and disperse to break light into individual spectral component; ii. said dispersed multi-spectral component lights strike the second equilateral prism (904) at an angle substantially equivalent to the exit angle from the first equilateral prism (903) in order for said component lights to be diffracted and transmitted as substantially parallel beams going out from said second equilateral prism; iii. said illuminated light beams passing through at least one colour filter and at least one focusing lens to filter out unwanted colour spectrums and at the same time to focus the intended colour component lights before said substantially parallel beams strikes the said beam splitter (603); iv. said substantially parallel multi-spectral component lights strike the beam-splitter (603) to generate a co- linear multi-spectral lights towards said solar cell surface; v. said the intended colour component lights are reflected (908) and transmitted from said solar cell surface; vi. said intended colour component lights (118) are individually directed by a plurality of reflective mirrors (116, 117) towards a plurality of single-spectral line scan camera (111, 112, 113). 4. BRIEF DESCRIPTION OF THE DRAWINGS

Other aspect of the present invention and their advantages will be discerned after studying the Detailed Description in conjunction with the accompanying drawings in which:

FIG. 1 shows a conventional method of line scan optical setup consists of the camera and line light which is set at an angle relative to each other. FIG. 2 shows a conventional method of line scan optical setup consists of the camera and line light which is set at an angle relative to each other towards a warped surface cell.

FIG. 3 shows the reflected light angle is identical to the angle of incident light when it is projected on flat surface and the amounts of refractions is depends on surface property and smoothness.

FIG. 4 shows the normal line shifted to different angle due to the curvature profile of a warped surface.

FIG. 5 shows another prior art by using two or multiple line lights which are mounted at the same angle on both side of the camera.

FIG. 6 shows an embodiment of the present invention for multiple scan single pass line scan apparatus.

FIG. 7 shows a glass plate used as beam splitter to produce co-linear lighting. FIG. 8 shows a cube used as beam splitter to produce co-linear lighting. FIG. 9 shows a multiple scan single pass line scan optical apparatus, wherein multi-sensor and multi-spectral line scan camera is used in the present invention.

FIG. 10 shows a multiple scan single pass line scan optical apparatus, wherein a plurality of line scan cameras or a plurality of monochromatic line scan cameras is used in the present invention.

FIG. 11 shows a comparison for the image quality obtained using a conventional angular line light setups and a co-linear line light setup.

FIG. 12 shows the importance of using multi-colour plan to ease the image processing.

5. DETAILED DESCRIPTION OF THE DRAWINGS

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those or ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well known methods, procedures and/ or components have not been described in detail so as not to obscure the invention. The invention will be more clearly understood from the following description of the embodiments thereof, given by way of example only with reference to the accompanying drawings which are not drawn to scale. Referring now to FIG. 6, there is shown an embodiment of the present invention for multiple scan single pass line scan apparatus, comprises of at least one line scan imaging device (601), at least one beam splitter (603) and at least one light beam (605) having a plurality of wavelengths illuminated from an illumination source (607). The present invention is using a co-linear line light method, whereby collimated light is projected substantially perpendicular onto a solar cell surface or warped solar cell and said light beam is reflected almost at the same angle of said projected light and reach the said imaging device sensors (601) at the smallest deflected angle. Hence high contrast image is obtained. Beam splitter (603) is used to make the said projected light coincides with said reflected light. Said beam splitter (603) includes but not limited to a glass plate (701) or a cube (801), which is further illustrated in FIG. 7 and FIG. 8.

Referring now to FIG. 7, there is shown a glass plate (701), which includes a half-silvered mirror coated glass plate used as beam splitter (603) to produce co-linear lighting. When an incident light beam strikes towards the said beam-splitter glass plate for example at an angle of 45 degree, said glass plate splits the said incident light to a certain percentage ratio, wherein certain percentage is being transmitted and the remaining percentage is being reflected. Said percentage ratio can vary depending on the angle between the incident light and the said beam splitter (603). In general, the larger the angle between the incident light and the said beam splitter (603), the larger the percentage of light is being reflected and the remaining percentage is being transmitted. Said reflected light beam strikes towards a solar cell surface and thereafter is reflected back and is passed through the said beam splitter plate (701) and eventually reach the said line scan imaging device sensor (601).

Referring now to FIG. 8, there is shown a cube (801) used as beam splitter (603) to produce co-linear lighting. Said cube comprises of two triangular glass prisms which are attached by using adhesive coating material (803) at a certain predetermined thickness which may range from zero up to ten micrometer so that said light beam is reflected and transmitted according to a specific percentage ratio. Said beam splitter cube (801) is typically coated with a selected metallic or dielectric optical filter coating so that incident light beam is reflected and transmitted according to certain percentage ratio with negligible absorption loss. Said percentage ratio can vary depending on the angle between the incident light and the said beam splitter (603). Typically if the incident light is 45 degree from the said beam splitter (801), half of the light incident is transmitted at 45 degree angle and the remainder is reflected. Said reflected light is striking the surface of solar cell vertically and some will be reflected as diffused light due to the presence of the anti-reflective SiN2 layer at said solar cell. Said reflected light from surface of said solar cell hence pass through the beam-splitter cube (801) and eventually reaches the line scan imaging device sensor (601).

Referring now to FIG. 9, there is shown a multiple scan single pass line scan optical apparatus, wherein multi-spectral line scan imaging device (901) is used in the present invention. Said multi-spectral line scan imaging device includes a single polychromatic line scan camera (901) with a plurality of sensors (902). Preferably the said photosensor is a multi chips or multi sensor package solid state device which comprises of a plurality of linear sensors (902) and is aligned and spaced precisely to coincide with the respective focused line images. For example, multi sensor line scan CCD camera with resolution ranging from 2048 to 12288 photo elements or pixels per line can be used as the said imaging device in the present invention. If three colours are adopted, i.e. red, blue and green, three linear sensors are required. A distance of "D" is used to separate the said plurality of photo-sensor (902) arrays as shown in the enlarged view in FIG. 9. Said plurality of sensor (902) arrays is separated at a distance of 10 micrometer to 20 micrometer corresponding to separation distance of the said three colours or any parallel collimated lights. The three photo-sensor (902) arrays have common clock inputs for synchronization. The combined spacing precision of the colour component lights and the three photo-sensor (902) array detectors allows accurate coincidence of the detected images with the single line of image of the original. The said multiple scan single pass line scan apparatus further comprises of a pair of equilateral triangular prism (903, 904). Said pair of equilateral triangular prism (903, 904) is used to obtain the spectral component separation of an incident white light. At the said pair of equilateral triangular prism (903, 904), each of the said prisms (903, 904) is separated by a distance of "E", wherein said distance of "E" can be ranged from 10 mm to 12 mm. When an incident white light (605) from an illumination source (607) strikes the first equilateral prism (903), the said incident light will be dispersed, that is, to break light into individual spectral components or the red, green and blue bands when a particular coating material is used on the said prism (903). The occurrence of the dispersion is because of the angle of refraction is dependent on the refractive index of the prism material which in turn is slightly dependent on the wavelength of light that is travelling through it. This means that different wavelengths of light will travel at different speeds, and so the light will dispersed into the colours of the visible spectrum, with longer wavelengths (e.g. red, yellow) being refracted less than shorter wavelengths (e.g. violet, blue). In such an arrangement, the prism is placed at a position with the incident light beam adjusted such that the refracted beam is at minimum deviation whereby at the angle of minimum deviation both the incoming and outgoing light rays hit the surface approximately at the Brewster's angle, which is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface with no reflection. The dispersed multi- spectral component lights will strike the second equilateral prism (904) at an angle substantially equivalent to the exit angle from the first equilateral prism (903) in order for said component lights to be diffracted and transmitted as substantially parallel beams (906) going out from the said second equilateral prism (904), and thereafter collimated into substantially parallel beams. The exit angle from first equilateral prism (903) and striking angle at second equilateral prism (904) has dependency on refractive index of the prism material, light beam angle of incidence with the surface of first equilateral prism (903) and also the apex angle of the equilateral prism (903), whereby the range of angle is approximately 30 to 50 degree. Filter and focus lens unit (905) is used to further refined the beams with high focus and accurate wavelength before the parallel multi-spectral component lights (907) striking the beam-splitter (603) to generate a co-linear multi-spectral lights. Preferably said filter and focus lens unit (905) comprises of at least one colour filter and at least one focusing lens to filter out unwanted colour spectrums and at the same time to focus the intended colour component lights. The focusing of the intended colour components is important in order to reduce interference from adjacent colour spectrum. Therefore when all the intended colour component lights are reflected to the said multi-spectral sensor camera (902), multi-colour image planes can be produced in said single polychromatic line scan camera (901). Referring now to FIG 10, there is shown a multiple scan single pass line scan optical apparatus, which is in another embodiment of the present invention. In this second embodiment of the present invention, almost same optical setup is used, whereby said multiple scan single pass line scan optical apparatus comprises of at least one line scan imaging device (601), at least one beam splitter (603), at least one light beam (605) illuminated from an illumination source (607) and a pair of equilateral triangular prism (903, 904) Said line scan imaging device (601) comprises of a plurality of single-sensor line scan cameras (111, 112, 113), coupled with a plurality of dichroic mirrors (114, 115) and a plurality of reflective mirrors (116, 117). Said plurality of monochromatic line scan cameras (111, 112, 113) is used to obtain multiple colour image planes. Preferably the photo-sensor arrays used are multiple single-sensor line scan camera with highest spectral response at a particular wavelength. Said dichroic mirrors (114, 115) are used to direct the light to the imaging device sensor of the individual monochromatic line scan camera (111, 112, 113) accordingly. As shown in FIG. 10, the reflected spectral lights (118) coming out from the beam-splitter (603) are striking the first dichroic mirrors (114) at a particular angle, in which 45 degree is an example reflects the blue spectral band (approximately 450nm to 495nm) while transmitting the green and red spectral bands (approximately 495nm to 750nm). The blue band is striking a first reflective mirror (116) at a particular angle, in which 45 degree is an example and reflected, traveling towards and reaches the first line scan camera (111) which is highly responsive towards blue spectral band. The green band striking a second dichroic mirror (115) at a particular angle, in which 45 degree is an example, is reflected and striking a second reflective mirror (117) at a particular angle, in which 45 degree is an example and reflected, traveling towards and reaches the second line scan camera (112) which is highly responsive towards green spectral band. The red spectral band which is un-reflected by the second dichroic mirror (115) travels and reaches the third line scan camera (113) which is highly responsive towards red spectral band. Thus, separation of red, green and blue spectral bands of the incident spectral bands through said plurality of dichroic mirrors and reflective mirrors is an example beams with substantially parallel distance separation which is solely determined by dichroic coating and reflective indexes of said dichroic mirrors. The order in which the reflected colour bands have been presented is by example only. Referring now to FIG 11, there is shown a comparison for the image quality obtained using a conventional angular line light setups and a co-linear line light setup. Sample Image A and Sample Image B were captured using angular line light setups, in which the middle area of the cell was found dark. This is because the lights are reflected away from the photo sensor of the line scan camera, and the different appearance of the dark area at Sample Image A and Sample Image B is due to the warping direction of the solar cell. Sample Image C is captured using the co-linear line light setup of the present invention, which showed the effectiveness to produce a high uniformity of contrast on the solar cell surface and undisturbed by the warp surface of solar cell.

Referring now to FIG. 12, there is shown the examples of using multi-spectral images to discern various chromatic defects accurately by having dedicated image planes for each type of defects, as some chromatic defects are only visible under the illumination and processing of a specific light spectral or colour plane. After all the intended colour component lights are reflected to the said line scan imaging device (601), multi-colour image planes can be produced by using of at least one image processing tool. Said image processing tool is used to extract colour in different colour planes, whereby said colour planes can be from colour space such as RGB, HSL, CYMK etc. For example, Sample Image D as shown in FIG. 12 is in blue colour plane which represent the original image of solar cell with defects and is predominantly used to compute blue colour homogeneity and variance of said solar cell. Sample Image E is in hue colour plane and is used to determine the solar cell colour, this colour space as different colours have different constant hue value. Sample Image F is in red colour plane but appears as black and white image by using the monochromatic sensor or camera. As said red plane has the most insensitivity towards blue colour, red plane will give very high contrast image compared to grey image as well as the original blue colour image. Therefor the red colour plane is used predominantly to extract finger print (horizontal white lines) and busbar (vertical white lines) information such as dimension, contamination, interruption, shape, irregularity and etc. since the white lines are most visible under the red colour plane. Sample Image G is in saturation plane, and usually the blue colour of solar cell has high saturation value and the saturation value represents the brightness of the colour. Surface defects which have colours other than blue (e.g. dirts, scratches, stains, contaminations and etc.) usually having lower saturation value compared to solar cell, thus it is used to detect solar cell surface defects, foreign particles and contamination. For example, a contamination spots on the lower right become significantly visible when saturation plane is used compared to other colour planes. While the preferred embodiment of the present invention and their advantages have been disclosed in the above Detailed Description which is an example only, the invention is not limited thereto but only by the scope of the appended claim.

Claims

WHAT IS CLAIM IS:

A multiple scan single pass line scan apparatus for solar cell inspection comprising: at least one line scan imaging device (601); at least one light beam (605) having a plurality of wavelengths illuminated from an illumination source (607); characterized in that said apparatus further comprising of at least one beam splitter (603) to direct said illuminated light beam (605) to be projected substantially perpendicular onto a solar cell surface and said light beam is reflected almost at the same angle of said projected light and reach the said line scan imaging device (601).

A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 1, wherein said beam splitter (603) comprises of a half-silvered mirror coated glass plate (701). A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 1, wherein said beam splitter (603) is a cube (801) comprises of two triangular glass prisms.

A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 3 wherein said triangular glass prisms are attached together by using adhesive coating material (803) at a predetermined thickness which may range from zero up to ten micrometer so that said light beam is reflected and transmitted according to a specific percentage ratio.

A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 3 wherein said cube (801) is coated with a selected metallic or dielectric optical filter coating so that said light beam is reflected and transmitted according to a specific percentage ratio.

A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 1 further comprises of a pair of equilateral triangular prisms (903, 904), wherein each of said prisms is separated by a distance of 10 mm to 12 mm so that the spectral component separation of an incident white light is obtained and said multi-spectral components are transmitted as substantially parallel beams going out from said prisms.

A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 1 further comprises of at least one colour filter and at least one focusing lens (905) to filter out unwanted colour spectrum and to focus the intended colour component lights.

8. A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 1 wherein a multi-spectral line scan imaging device is used as said line scan imaging device (601).

A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 8 wherein said multi-spectral line scan imaging device can be a single polychromatic line scan camera (901) with a plurality of sensors (902).

10. A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 9 wherein a plurality of linear sensors (902) are required in said imaging device (901) for a plurality of intended colour component lights.

. A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 9 wherein said plurality of linear sensor (902) arrays is separated at a distance of ten micrometer to 20 micrometer corresponding to separation distance of any parallel collimated lights.

A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 1 wherein a plurality of single- sensor line scan cameras (111, 112, 113)is used as said line scan imaging device (601).

A multiple scan single pass line scan apparatus for solar cell inspection as claimed in Claim 12 wherein said plurality of line scan cameras (111, 112, 113) are coupled with a plurality of dichroic mirrors (114, 115) and a plurality of reflective mirrors (116, 117) to direct the individual spectral band to respective line scan camera (111, 112, 113). A methodology of multiple scan single pass line scan for solar cell inspection comprising steps of: i. projecting a light beam (605) from an illumination source (607) towards a solar cell surface; ii. providing at least one line scan imaging device (601) to detect the reflected light from said solar cell surface; iii. acquiring images from said line scan imaging device (601); characterized in that said methodology further comprises of following steps before said reflected light is detected by said line scan imaging device: i. said light beam (605) having a plurality of wavelengths from an illumination source (607) strikes the first equilateral prism (903) and disperse to break light into individual spectral component; said dispersed multi-spectral component lights strike the second equilateral prism (904) at an angle equivalent to the exit angle from the first equilateral prism (903) in order for said component lights to be diffracted and transmitted as substantially parallel beams going out from said second equilateral prism (904); said illuminated light beams passing through at least one colour filter and at least one focusing lens (905) to filter out unwanted colour spectrums and at the same time to focus the intended colour component lights before said substantially parallel beams strikes the said beam splitter (603); said substantially parallel multi-spectral component lights strike the beam-splitter (603) to generate a co- linear multi-spectral lights towards said solar cell surface; v. the intended colour component lights (118) are reflected and transmitted to the multi spectral sensor imaging device. A methodology of multiple scan single pass line scan for solar cell inspection comprising steps of: i. projecting a light beam (605) from an illumination source (607) towards a solar cell surface; ii. providing at least one line scan imaging device (601) to detect the reflected light from said solar cell surface; iii. acquiring images from said line scan imaging device (601); characterized in that said methodology further comprises of following steps before said reflected light is detected by said line scan imaging device: i. said light beam (605) having a plurality of wavelengths from an illumination source (607) strikes the first equilateral prism (903) and disperse to break light into individual spectral component; said dispersed multi-spectral component lights strike the second equilateral prism (904) at an angle substantially equivalent to the exit angle from the first equilateral prism (903) in order for said component lights to be diffracted and transmitted as substantially parallel beams going out from said second equilateral prism (904); said illuminated light beams passing through at least one colour filter and at least one focusing lens (905) to filter out unwanted colour spectrums and at the same time to focus the intended colour component lights before said substantially parallel beams strikes the said beam splitter (603); said substantially parallel multi-spectral component lights strike the beam-splitter (603) to generate a co- linear multi-spectral lights towards said solar cell surface; v. said intended colour component lights are reflected and transmitted from said solar cell surface; vi. said intended colour component lights (118) are individually directed by a plurality of dichroic mirrors (114, 115) and a plurality of reflective mirrors (116, 117) towards a plurality of single-spectral line scan camera (111, 112, 113).

A methodology of multiple scan single pass line scan for solar cell inspection as claimed in Claim 14 or 15 wherein said step of acquiring images from said line scan imaging device (601) is carried out by using of at least one image processing tool to extract colour in different colour planes so that surface feature information of said solar cell is detected from said colour planes.

A methodology of multiple scan single pass line scan for solar cell inspection as claimed in Claim 14 or 15 wherein said acquired image in blue colour plane is used to compute blue colour homogeneity and variance of said solar cell.

A methodology of multiple scan single pass line scan for solar cell inspection as claimed in Claim 14 or 15 wherein said acquired image in hue colour plane is used to determine the colour of said solar cell based on hue value.

A methodology of multiple scan single pass line scan for solar cell inspection as claimed in Claim 14 or 15 wherein said acquired image in red colour plane is used to extract finger print and busbar information of said solar cell to determine irregularities such as broken finger print or busbar.

A methodology of multiple scan single pass line scan for solar cell inspection as claimed in Claim 14 or 15 wherein said acquired image in saturation colour plane is used to identify the non-blue surface defects such as contamination, scratches or presence of foreign particles at said solar cell.