Patent Application
20110012635
Embodiments of the present invention generally relate to apparatus and processes for testing and qualifying a photovoltaic device in a production line.
Photovoltaic (PV) devices, or solar cells, are devices which convert sunlight into direct current (DC) electrical power. Typical thin film PV devices, or thin film solar cells, have one or more p-i-n junctions. Each p-i-n junction comprises a p-type layer, an intrinsic type layer, and an n-type layer. When the p-i-n junction of the solar cell is exposed to sunlight (consisting of energy from photons), the sunlight is converted to electricity through the PV effect.
Typically, a thin film solar cell includes active regions, or photoelectric conversion units, and a transparent conductive oxide (TCO) film disposed as a front electrode and/or as a back electrode. The photoelectric conversion unit includes a p-type silicon layer, an n-type silicon layer, and an intrinsic type (i-type) silicon layer sandwiched between the p-type and n-type silicon layers. Several types of silicon films including microcrystalline silicon film (μc-Si), amorphous silicon film (a-Si), polycrystalline silicon film (poly-Si), and the like may be utilized to form the p-type, n-type, and/or i-type layers of the photoelectric conversion unit. The backside electrode may contain one or more conductive layers.
With traditional energy source prices on the rise, there is a need for a low cost way of producing electricity using a low cost solar cell device. Conventional solar cell manufacturing processes are highly labor intensive and have numerous interruptions that can affect the production line throughput, solar cell cost, and device yield. For instance, conventional quality inspection of solar cell devices is typically either only conducted on fully formed solar cell devices via performance testing or on partially formed solar cell devices that are manually removed from the production line and inspected. Neither inspection scheme provides metrology data to assure the quality of the solar cell devices and diagnose or tune production line processes during manufacturing of the solar cell devices.
Therefore, there is a need for an automated test apparatus for photovoltaic substrates that provides for automated testing in a compact, easily maintained unit for use in high-volume manufacturing facilities.
Embodiments described herein provide an apparatus for processing a solar cell substrate comprising a test apparatus, which comprises a test fluid enclosure, an electrical sensor disposed in the test fluid enclosure, and a substrate support having a frame for handling a substrate, a connection pod for making electrical connection with connectors disposed within the substrate, and a motion assembly for positioning the substrate, and a cleaning apparatus, which comprises a rinse station configured to spray a rinsing fluid on two surfaces of the substrate and a gas knife for removing liquid from the substrate.
Other embodiments provide a test apparatus for a solar cell manufacturing line comprising an entry conveyor for transporting solar cell substrates from the solar cell manufacturing line to the test apparatus, an attachment device for attaching a junction box to the solar cell substrate, a solar simulator configured to flash solar spectrum radiation and sense electric current produced by the solar cell substrate, and a high potential tester comprising a test fluid enclosure for containing an electrolyte test fluid, an electrical sensor disposed in the test fluid enclosure, a substrate handler configured to engage with the substrate and dispose the substrate in the electrolyte test fluid, the substrate handler comprising a connection pod configured to make electrical connection with the junction box, a power supply connected to the connection pod and the electrical sensor, a rinse dry station, and an exit conveyor for delivering substrates from the test apparatus to the solar cell manufacturing line.
Other embodiments provide a method of processing a solar cell substrate comprising disposing the substrate in a test fluid, applying a voltage to contacts disposed within the substrate, sensing electric current emerging from an edge of the substrate into the test fluid using a current sensor immersed in the test fluid, removing the substrate from the test fluid, rinsing the test fluid from the substrate, and drying the substrate using a gas knife.
So that the manner in which the above-recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
Embodiments of the invention generally provide methods and apparatus for processing and qualifying a formed photovoltaic device to assure that the formed photovoltaic device meets desired quality and industry electrical standards. Embodiments of the present invention may also provide a photovoltaic device, or solar cell device, production line that is adapted to form a thin film solar cell device by accepting an unprocessed substrate and performing multiple deposition, material removal, cleaning, bonding, and testing steps to form a complete functional and tested solar cell device. The solar cell device production line, or system, is generally an arrangement of processing modules and automation equipment used to form solar cell devices that are interconnected by automated material handling system. In one embodiment, the system is a fully automated solar cell production line that is designed to reduce and/or remove the need for human interaction and/or labor intensive processing steps to improve the device reliability, process repeatability, and the solar cell formation process cost of ownership (CoO).
One set of embodiments provides an apparatus that is used to test and qualify the electrical isolation of a photovoltaic device that is formed on a substrate and encapsulated within a composite solar cell structure from the external environment. The apparatus, or electrical testing module, generally comprises a substrate receiving region, a wet electrical isolation testing region, a substrate cleaning region, and an automation control system. During processing the electrical testing module is configured to received a fully formed solar cell device, transfer the formed solar cell device to the testing region in an automated fashion, perform one or more electrical qualification tests, transfer the formed solar cell device to the substrate cleaning region in an automated fashion, and perform one or more cleaning processes on the formed solar cell device. In one embodiment, the one or more electrical qualification tests comprises a wet high potential qualification test that is used to assure that the formed solar cell device meets desired quality and industry electrical isolation standards.
An apparatus for conducting a wet high potential test of a solar cell device generally comprises a tank for contacting the solar cell device with a test fluid, which may comprise a surfactant solution, possibly including water and/or other aqueous media.
In one embodiment, the automation assembly 201 comprises a gantry 208, motion assembly 214 and a plurality of connection pods 222a-222c that are used to position one or more solar cell substrates with respect to the test tank 204 and other components of the apparatus 100 of
Each of the connection pods 222a-222c has a seal 240a-240c, respectively, that seals the electrical connection between the connection pod 222 and the substrate. In one embodiment, connectors disposed in the substrate are collected in a junction box near the center of the substrate for easy access. A connection pod 222 may connect by mating with connectors in a junction box. The seal 240 couples to the connection pod 222 and the junction box to prevent test fluid from entering the junction box or the connection pod when the substrate is exposed to the test fluid.
In another embodiment, each of the connection pods 222 has a plurality of seals that mate with the connectors in the connection pod and the connectors in the junction box to seal each individual connection made between the test apparatus and the substrate. In another embodiment, the plurality of seals may include connector seals as well as a junction box seal of the type described above.
The support 224 comprises one or more shafts, rods, or connectors 216 that couple the support 224 to a motion assembly 214. The motion assembly generally raises and lowers the support 224 to position a substrate in a test position or to transport the substrate into and out of the test apparatus 200. The support 224 also comprises one or more cross members 218 that engage with and hold a substrate using attachment vectors 220. The attachment vectors 220 may be suction cups for certain substrates. The attachment vectors 220 generally contact a major surface of the substrate to hold it in place for testing. In one embodiment, attachment of the substrate to the attachment vectors 220 is maintained by vacuum. In another embodiment, an attachment vector may comprise opposable members that contact opposite major surfaces of the substrate. In yet another embodiment, a substrate may be held in place and manipulated by edge grippers, which may contact the edge portions or corner portions of a substrate. Each of the connection pods 222, which are connected to the support 224, has two or more probes that are generally used to probe the positive and negative leads of the solar cell. Each connection pod 222 is configured to deliver voltage to its connected substrate during a test procedure. In one embodiment, the probes and connectors within a connection pod 222 engage with connectors disposed within the junction box disposed on a substrate, establishing electrical connection therewith.
The tank 204 comprises a plurality of sensors 228, 230, and 232. A level sensor 228 indicates the liquid level in the tank 204 and is used to ensure sufficient test fluid A in the tank 204 for testing. A temperature sensor 230 is used to control the temperature of the test fluid A to ensure the test fluid A has adequate conductivity. A conductivity sensor 232 is used to control the concentration of electrolyte in the test fluid A. Two sets of sensors are provided to enable operating two test portions of the tank 204 by lowering the liquid level to a height below the height of the divider 234. In operation, test fluid medium or solvent is added if a level sensor indicates the level of test fluid A in the tank 204 is too low. Electrolyte is added to the test fluid A if a conductivity sensor 232 indicates the conductivity of the test fluid A is too low. The test fluid A is warmed or cooled in response to indication from the temperature sensor 230 that the test fluid temperature is out of a specified range.
In one embodiment, each test portion of the tank 204 has a drain (not shown) that operates independent of the other test portion to allow selective control of the test fluid level of each test portion. When the tank 204 is operated as a single test facility, with test fluid level 226 above the height of the divider 234, one or both drains may be used to control the test fluid level. When the tank 204 is operated as two or more test portions, each drain is used to control the liquid level in its test portion.
Substrates may be supported by any convenient configuration of support members. In one embodiment, the cross-member 324 may be replaced by a carriage comprising a plurality of cross-members, each coupled to the gantry 208 by a set of translators 314. Additionally, more than one substrate handling member 326 may be provided. In other embodiments, curved or angled members may also be provided to connect the various support members, improving the rigidity of the support structure. Providing more support members may improve handling of substrates in some embodiments by constraining undesirable motion vectors such as flexing and wobbling.
The test tank 204 comprises a first electrode 345A disposed in the test tank 204. The first electrode 345A is configured to detect current emerging from the solar cell substrate “S” disposed in the test fluid “A”. A second electrode 345B, similar to the first electrode, may be disposed in the test tank 204 as well. The second electrode 345B provides a redundant current reading as a way to check the accuracy of current readings from both electrodes 345. As is described further below, the second electrode 345B also allows operating the test tank 204 as two separate test stations. A power supply 350 is connected to the connection pods 316 to deliver power to the junction box “J” of the substrate S. The electrodes 345 are also connected to the power supply 350 to complete the test circuit. In one embodiment, the electrodes 345 are current sensors disposed in an interior portion of the tank to facilitate exposure to the test fluid A. In another embodiment, each of the electrodes 345 may be a distributed sensor, such as a continuous conductor, which may be a plate, a wire, or a plurality of plates or wires, disposed around an outer portion of the tank 204 or around the wall of the tank 204. In another embodiment, each of the electrodes 345 may be a distributed array of current sensors each connected individually to the power supply 350 or to a current collector connected to the power supply 350.
The divider 234 extends from the floor of the tank 204 to a height less than a maximum height of the test fluid A in the tank 204. The divider 234 generally defines a plurality of test zones in the tank 204. By lowering the test fluid level to a height below the height of the divider 234, the tank 204 is divided into two test zones that may be operated independently. The divider 234 also provides additional support under a single substrate when operating the tank 204 as a test facility for single large substrates. In some embodiments, a single substrate being processed in the tank 204 may rest on an upper surface of the divider 234. The divider 234 may be formed integrally with the tank 204, or attached to the floor of the tank 204. If the tank 204 comprises molded plastic, the divider 234 may be formed as part of the molded shape of the tank 204. Alternately, the divider 234 may be attached to a plastic tank material using adhesive or by solvent or thermoplastic welding. In embodiments featuring continuous current sensors disposed along the tank wall 238, the sensor will also be disposed along the divider 234.
Use of a single divider 234 divides the tank 204 into two test zones. More test zones may be created by including more dividers in the tank. For example, use of two substantially parallel dividers may create three test zones in a tank. Appropriate extension of the support structure and sensor network would then enable simultaneous processing of three substrates. In another example, use of two dividers that intersect in a right angle will create up to four separate test zones. If the two dividers have different heights, the tank 204 may be divided into two test zones or four test zones to accommodate substrates of different sizes. It will be understood that placement of support structures, sensors, and connection pods may be adjusted to access the multiple test zones.
The tank 204 further comprises a plurality of sensors 228, 230, and 232, for sensing liquid level (228), temperature (230), and conductivity of the test fluid (232). As described above in connection with
In operation, a solar cell substrate “S” is delivered to the apparatus 100 from a solar cell fabrication line using a conveyor that delivers the solar cell substrate S to the attachment apparatus 102. After a junction box “J” is attached to the substrate S, the conveyor 112 delivers the substrate S to the solar simulator 104 for solar flash testing. The conveyor 114 then delivers the substrate S to the high potential test apparatus 106. The automation assembly 201 receives the substrate S from the conveyor 114. The automation assembly 201 is positioned above the conveyor 114 when receiving the substrate S. After the substrate S is positioned on the automation assembly 201, the automation assembly 201 moves the substrate S into a test position in which the substrate S is substantially immersed in the test fluid A. The automation assembly 201 moves along the gantry 208 by virtue of an actuated motion assembly, such as the translators 314 of
As shown in
The rinse and dry station 306 of
The dryer 320 comprises a gas knife positioned to direct a stream of gas toward the substrate. The gas knife will generally apply a drying gas to both sides of the substrate, as with the rinser 318. The gas may be air, nitrogen, or another non-reactive gas, and the gas may be heated to facilitate drying. In one aspect, the gas stream physically removes fluid from the substrate by propelling the fluid from the substrate surface. In another aspect, the gas stream encourages evaporation of the rinse fluid from the substrate surface. The gas knife may be oriented to direct gas substantially perpendicular to the substrate surface, or at any desired angle.
At 406, a test voltage is applied to the contacts. The test voltage is applied by ramping the voltage up from 0 to a target voltage. The target voltage is determined by the amount of dielectric resistance the substrate is designed to provide and the desired signal current for detecting breakthrough. In some embodiments, the signal current will be between about 10 μA and about 70 μA. A sensor is disposed in the test fluid to detect any current leaking from the solar cell substrate. Should there be a defect in the substrate, current will flow from the conductors disposed within the substrate, through the dielectric flaw into the conductive liquid, which will conduct the current to the sensor.
At 408, the substrate is removed from the test tank and maneuvered into a cleaning apparatus. The test fluid is generally rinsed off the substrate using a water spray, or another appropriate rinse fluid, such as an aqueous or organic solvent or some mixture thereof, which may be delivered to the top and bottom of the substrate simultaneously. At 410, the substrate is then dried using a gas knife. The gas knife directs air, or another drying gas such as nitrogen, against the substrate in a thin, high-velocity sheet to evaporate and physically remove liquid from the substrate. In some embodiments, the gas knife may be configured to apply the air sheet to the substrate at an angle to enhance removal of liquid.
At 604, the solar cell substrate is positioned over a test tank for performing a wet high potential test, such as any of the embodiments described elsewhere herein, or any other convenient embodiment of test enclosure. Instead of a tank, a test tray may be used in some embodiments. Positioning may be accomplished through any convenient means, such as proximity switches coupled to linear actuators that move the substrate connected to the probe.
At 606, the substrate is lowered into the test tank. The tank contains a test fluid that provides a conductive medium for detecting current leakage from the solar cell substrate when a high voltage is applied to the connection site. The test fluid may be an aqueous surfactant solution in some embodiments. The substrate is immersed in the test fluid at 608, such that the test fluid contacts the probe nest. This ensures that any current leakage from any part of the solar cell substrate is conducted through the test medium to current sensors disposed in the test tank.
At 610, a test voltage is applied to the substrate connection site through the probe. Current will leak through any structural dislocations, such as air bubbles or impurities, in the material of the solar cell substrate, and will emerge into the test fluid. The test fluid conducts the fugitive current to sensors disposed in the test tank. Generally, at least about 500 V is applied to the substrate, or in some embodiments at least 1,000 V, depending on the size and rated voltage of the substrate. Detected current greater than about 40 mA generally indicates unacceptable leakage.
At 612, the substrate is raised out of the test tank, and at 614, the substrate is transferred to a rinse/dry station, where a cleaning fluid is applied to remove any remaining test fluid, and a gas knife dries the substrate.
The lift assembly 740 of
The substrate support surface 750 may be a conveyor in some embodiments. In the embodiment of
The probe assembly 770 comprises a base 772, a probe support member 774, an extension arm 776, and a probe nest 778. The probe assembly 770 positions the probe nest 778 to contact the connection site 754 of the substrate, making an electrical connection between one or more probes in the probe nest 778 and conductors disposed within the substrate. The extension arm 776, probe support member 774, and probe nest 778 may each, or all, be actuated to position the probe nest 778 for connecting to the connection site 754.
The probe assembly 770 and the lift assembly 740 may be rotationally actuated as well. One of both of the lift support member 744 and the probe support member 774 may be rotatably coupled to their respective bases 742 and 772. A rotational coupling would enable the lift support member 756 to rotate from a position proximate to the test enclosure 716 to a position away from the test enclosure for collecting and delivering substrates to and from other processing equipment. A rotational coupling would likewise enable the probe support member 774 to function with more than one test enclosure 716 by rotating among a plurality of test stations.
While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1685/CHE/2009 | Jul 2009 | IN | national |
