Claims:WE CLAIM:

1. Set-up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately comprising a light source with LEDs (1) to illuminate large area silicon solar cell (4) to be tested, wherein data logger (5) is placed on the Si solar cell (4) and the light source with LEDs (1) is connected to regulated DC power supply (2).
2. The set-up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately as claimed in claim 1, wherein the light source with LEDs (1) includes a plurality of LEDs (1A) of different wavelength mounted on a plate (1B), in which the LEDs are powered by the regulated DC power supply (2).
3. The set-up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately as claimed in claim 1 or2, wherein the LEDs of different wavelengths are distributed uniformly on the plate, the different wavelengths include 365, 380, 400, 425, 440, 470, 490, 500, 525, 535, 550, 565, 585, 595, 615, 635, 660, 700, 740, 770, 850 and 940 nm.
4. The set-up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately as claimed in claim 3, wherein each set of single wavelength LED is powered separately through a potential divider for adjustment of intensity of each wavelength independently.
5. The set-up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately as claimed in claim 1-4, wherein the solar cell (4) is clamped onto vacuum chuck (3).

6. The set-up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately as claimed in claim 1-5, wherein the data logger (5) records data of the current (I) produced by said cell (4).
7. The set-up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately as claimed in claim 1-6, wherein the light source with LEDs (1) is connected to PLC (6) for automation in controlling the LED light source (1) by switching on the LEDs (1A) of different wavelength.
8. The set-up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately as claimed in claim 1-7, wherein the set up is housed in a light proof box that external light does not introduce any error. , Description:Set-up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately
FIELD OF INVENTION
[001] This invention relates to a set-up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately. The set-up is provided with light source of high intensity and different wavelengths using LEDs to measure quantum efficiency (QE) and Current, Voltage (IV) of silicon solar cell to reveal various losses in the cell with much more ease and accuracy than the conventional system.
BACKGROUND/PRIOR ART OF THE INVENTION
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[003] Solar cells are being produced in large number globally. The cell efficiency is of critical importance as it decides the cost per watt of the solar power and higher the efficiency lesser will be the land and balance of systems requirement. There are various methods of finding the loss in a cell which have been adopted from the available characterization equipment of microelectronics where the size of the sample was a few sq mm or a few sq cm.
[004] Solar cell is large area diode and commercial solar cells are being produced with cells area as big as 245 sq cm. Measurement of quantum efficiency using conventional Quantum efficiency (QE) set up, where the light is incident on about 2 sq mm area, is not very accurate when extrapolated to 245 sq cm area.
[005] This is because a small area of 2 sq mm has to cover the entire large area separately leading to large number of readings followed by determining average value of readings. This consumes lots of time with high chances of inaccuracy. Further, some area of large solar cell may be missed out while taking measurement.
[006] Hence a new concept has been conceived where the light source will be made using high intensity LEDs of various wavelengths and QE and IV will be measured which will throw light on different loss mechanisms in the large area solar cells with accuracy and will help enhance the cell efficiency.
[007] Now, reference may be made to the following patents.
[008] US6946858B2 deals with a measuring method for generating current voltage (IV) data of a solar cell by illuminating the substrate as well as a reference device at the same time while detecting an irradiance of said light using said reference device. The invention lies in a light responsive time constant of a irradiance detection circuit in which said reference device is used and adjusted so that said light responsive time constant of said irradiance detection circuit comes closer to a light responsive time constant of said photoelectric conversion device. There is an apparatus for practicing said measuring method. This uses light similar to spectrum of the sun and not LED of different colours as done in the present invention.
[009] US20120222741A1 describes about how a solar cell is fabricated which gets prone to light induced degradation. This patent also discloses silicon solar cells with a silicon-based substrate comprising boron, oxygen and carbon, and an antireflective coating (ARC) containing at least one carbon-containing layer adjacent to the substrate.
[010] US20100276571A1 discloses a method of calibrating a light source employed to simulate the sun in solar cell testing apparatus using a control cell. This helps in carrying out accurate measurement of the solar cells and has no effect of light intensity fluctuations during measurement.
[011] The concept of aforesaid second and third patents is entirely different from the proposed patent application.
[012] JP5615909B2 is related to measurement of quantum efficiency (internal and external) without disturbing the sample, cabling and electronics. It is different from present patent because here QE is measured on full cell area along with IV curve at some discrete wavelengths.
[013] Thus, none of the above can fulfill the requirements of the present invention for which it is designed.
[014] Si solar cells are fabricated on a 6”x 6” Si wafers. This is required as the incident solar radiations are quite diluted and in order to capture more sunlight, large area devices are cost effective. When it comes to testing and characterization of large area Si solar cells for quantum efficiency measurement (QE), available test equipments are used which are generally designed for small area microelectronic devices. In these conventional equipment light of different wavelength starting from UV to IR is obtained by moving a grating in the path of a white light source. After passing through the grating the light is so weak that it has to be chopped using a chopper so that the weak signal can be detected easily. The light of different wavelength is so weak that the short circuit current produced by the small area of a few sq. mm is in micro amperes. For measuring such small current with accuracy, one has to have very accurate electronics and meters which are very expensive and are not available indigenously in India.
[015] In order to overcome this problem a new concept is conceived where high intensity light source is developed for characterizing large area Si solar cells accurately.
OBJECTS OF THE INVENTION
[016] An object of the invention is to propose set up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately.
[017] Another object of the invention is to propose set up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately which obviates shortcomings of prior art.
[018] Another object of the invention is to propose set up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately which is simple in construction and cost effective.
[019] Still another object of the present invention is to provide set up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately which is efficient.
[020] Yet another object of the present invention is to propose set up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately which works faster.
[021] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.
SUMMARY OF THE INVENTION
[022] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.
[023] In this invention high intensity light source has been developed for characterizing large area Si solar cells accurately. LEDs of different wavelengths starting from Ultra Violet (UV) to Infra Red (IR) are used to illuminate the large area Si solar cells. The setup is designed using a light proof box and the LEDs are powered by a regulated power supply. Each set of LED with similar wavelength is powered separately so that the intensity of the light is adjusted as desired. Pyranometer is employed to measure and adjust the intensity of all the radiations before putting the set-up to operation. The absolute intensity is calibrated using a standard solar cell.
[024] According to this invention, there is provided set up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately comprising a light source with LEDs to illuminate large area silicon solar cell to be tested, wherein data logger is placed on the Si solar cell and the light source with LEDs is connected to regulated DC power supply.
[025] The light source with LEDs includes a plurality of LEDs of different wavelength mounted on a plate, in which the LEDs are powered by the regulated DC power supply.
[026] The LEDs of different wavelengths are distributed uniformly on the plate, the different wavelengths include 365, 380, 400, 425, 440, 470, 490, 500, 525, 535, 550, 565, 585, 595, 615, 635, 660, 700, 740, 770, 850 and 940 nm.
[027] Each set of single wavelength LED is powered separately through a potential divider for adjustment of intensity of each wavelength independently.
[028] The solar cell is clamped onto vacuum chuck.
[029] The data logger records data of the current produced by said cell.
[030] The light source with LEDs is connected to PLC for automation in controlling the LED light source by switching on the LEDs of different wavelength.
[031] The set up is housed in a light proof box that external light does not introduce any error.
[032] It is possible to measure QE of the full cell in a few seconds using the full area of the cell. This setup can also be used to draw IV characteristic of the full cell under different wavelengths of lights and these measurements throw more light on the cell characteristics which have not been explored till now.
[033] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
[034] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[035] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
[036] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:-
Figure 1 shows: Set up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately in accordance with present invention.
[037] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAIL DESCRIPTION OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS OF PREFERRED EMBODIMENTS
[038] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
[039] There are various methods of finding the loss mechanisms in a solar cell which have been adopted from the available characterization equipment of microelectronics where the size of the sample was a few sq mm to a few sq cm. Solar cell is large area diode and commercial solar cells are being produced with cells area as big as 245 sq cm. Optical measurement on small area and extrapolating results to large area is likely to give rise to errors as already discussed hereinabove.
[040] In order to address the prior issues of known technology, the present invention has been introduced in which high intensity light source has been developed for characterizing large area Si solar cells accurately. LEDs of different wavelengths starting from Ultra Violet (UV) to Infra Red (IR) are used to illuminate the large area Si solar cells. The setup is designed using a light proof box and the LEDs are powered by a regulated power supply. Each set of LED with similar wavelength is powered separately so that the intensity of the light can be adjusted as desired. Pyranometer can be used to measure and adjust the intensity of all the radiations. The absolute intensity is calibrated using a standard solar cell.
[041] Now, reference may be made to Figure 1 illustrating the present invention pertinent to a technology regarding set up to measure quantum efficiency and current voltage characteristics of large area solar cells accurately. According to the present invention, the set-up of invention comprises a light source with LEDs (1), Regulated Power Supply (2), Vacuum chuck (3), Solar cell (4) to be tested, Electronics for measurement (5) and PLC (6).
[042] The connectivity among the above with their functionality will be described herein below:
[043] Referring to figure 1, a plurality of LEDs (1A) of different wavelength are mounted on a plate (1B) constituting the light source with LEDs (1).
[044] LEDs of following wavelengths are distributed uniformly on the plate viz. 365, 380, 400, 425, 440, 470, 490, 500, 525, 535, 550, 565, 585, 595, 615, 635, 660, 700, 740, 770, 850 and 940 nm based on their availability which are then powered by the regulated DC power supply (2). This ensures that the intensity of LED light remains constant. Each set of single wavelength LED is powered separately through a potential divider so that intensity of each wavelength can be adjusted independently. The light source with LEDs (1) is employed to make the light incident on a solar cell (4) under test. The solar cell is clamped onto said vacuum chuck (3). The data of the current (I) produced by said cell (4) is recorded in data logger (5) placed on the solar cell as shown in the figure 1.
[045] LEDs of different wavelengths starting from Ultra Violet (UV) to Infra Red (IR) are provided. By using large number of LEDs, the intensity of the light can be increased to at least ~0.4 sun i.e. 40 mW/sq.cm. The LEDs have a very favorable property that the band width of the light is quite narrow (~50 nm). Hence by using large number of LED of various wavelengths a strong light source can be made. Another advantage of using LED is that the intensity of the light can be controlled by changing the voltage applied and the peak of the wavelength does not shift unlike in incandescent lamp.
[046] In conjunction with the above, there is provision of PLC (6) to be connected with the light source with LEDs (1) for automation in controlling the LED light source, wherein the PLC switches on the LEDs of different wavelength very fast in order of milli seconds. The aforesaid setup as best seen in fig. 1 is accommodated in a light proof box to avoid error.
[047] Initially prior to operation of the set-up for measurement, the light intensity is measured with the help of a pyranometer. This is done only once before using the set-up. Pyranometer has a very flat response to all the colors of light. The intensity of the different wavelength can be adjusted w.r.t longer wavelength say 770 nm.
[048] Suppose we get a value on the Pyranometer X for a voltage V for 770nm LEDs, the voltage for 740 nm will be reduced so that we get the Pyranometer reading as 740*X/770. Similarly, while going further for shorter wavelengths; the voltage to the LEDs will be reduced further so that we get same number of photons for every wavelength of light. The powering of LED can be very fast (in milli seconds) unlike incandescent lamps. Therefore, the LED light source is controlled by a PLC (6) which puts ON the LEDs of different wavelength very quickly (in less than a few seconds). The data of the current produced by cell will be recorded using data logger (5) and the total time required will be a few seconds only which is much faster than the conventional grating based system where it takes a few minutes i.e. few minutes for each 2 Sq mm area of solar cell to scan the full range of wavelengths. The absolute intensity of the light will be calibrated using a standard calibrated cell. This way we will be able to measure QE of the full cell without using any lock-in amplifier as the short circuit current of the full cell at 40% of the incident light will be very large (in the range of 0.1 A in comparison to conventional equipment which is in micro A) and will be measured using commonly available meters. There will be no requirement for extrapolating the measured values to large area as the measurements are being done on the actual area. The setup will be housed in a light proof box so that external light does not introduce any error.
[049] This setup can also be used to draw current, voltage (IV) characteristic of the full cell under different wavelengths of lights. The measurements can throw more light on the cell characteristics and decipher loss mechanisms viz. NIR parasitic absorption, non uniformity losses, reflectance losses etc.
Advantageous Features: -
- A simple and cost effective equipment for optical and electrical characterization of large area Si solar cells.
- Use of inexpensive commonly available meters for measurements.
- Measurement under higher intensity gives very strong signals, which results in measuring very accurate data.
- Very fast results as the total wavelengths are scanned in less than a few seconds.
- Simple to operate and derive output.
- Ease is manufacturing.
- No need of Lock in amplifier as signal to be measured is strong due to high intensity illumination.
- Determination of the loss areas in solar cell viz. NIR parasitic absorption, non uniformity losses, reflectance losses etc.
[050] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[051] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
[052] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogues to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.
[053] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.
[054] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[055] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[056] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.