This work is supported by the German Federal Ministry for Economic Affairs within the project &#8220;Feuerdrache&#8221; (0324205B). The authors thank the co-workers that contributed to this work and the project partners (InfraTec, Rehm Thermal Systems, Heraeus Noblelight, Trumpf Photonic Components) for co-financing and providing outstanding support.

1. Installation of IR camera into a conveyor belt furnace
<ol>
	<li>Decide which part of the furnace should be measured by the IR camera. 
	NOTE: Here, the peak zone of the firing process is chosen (see the orange highlighted zone in the firing area of Figure 1A).</li>
	<li>Define the temperature range of interest that the IR camera should detect (e.g., 700&#8722;900 &#176;C, the typical peak temperature range of the firing process).</li>
	<li>Determine, or at least estimate (through experiments or literature), the temperature,&#160;spectral, and angular dependent emissions of the object(s) of interest (e.g., silicon solar cell) to identify the wavelength range(s) of highest emission for the temperature range of interest (under a specific camera angle). 
	NOTE: Here, the emission is estimated based on previous literature3 and a software called RadPro10, which calculates the spectral, angular, and temperature-dependent emissivity for materials of interest.</li>
	<li>Deciding on the IR camera type 
	NOTE: Here, a midwave infrared (MWIR) indium antimonide (InSb) camera (Table of Materials) is used.
	<ol>
		<li>Choose a camera that can detect the temperature range of interest.</li>
		<li>Select a camera whose detection wavelength range matches the wavelength range of highest emission of the object of interest in the temperature range of interest.</li>
		<li>Avoid as much parasitic radiation detection by the camera as possible by avoiding objects that emit or reflect radiation into the camera field of view (e.g., IR lamps in a furnace).&#160;</li>
		<li>Decide on the necessary spatial and temporal resolution of the camera (e.g., 640 px x 512 px and 125 Hz [full image] for the used camera here).</li>
	</ol>
	</li>
	<li>Realize a sufficient optical path from the IR camera to object (see Figure 1B).
	<ol>
		<li>Avoid disturbing objects in the optical path (e.g., IR lamps causing direct or reflected light).</li>
		<li>Position the camera outside of the furnace chamber, if possible. 
		NOTE: Most cameras have low operating temperatures (e.g., up to 50 &#176;C). Make sure in advance that the camera position can be changed, if desired.</li>
		<li>Remove the furnace wall and isolation at the location where the optical path should be and replace the hole with an insulating IR window.
		<ol>
			<li>Choose the appropriate material for the window that meets the following demands: 1) as transparent as possible for the detection wavelength (&#955;) range of the camera (e.g., quartz glass window for ~0.2 &#181;m &#60; &#955; &#60; 3 &#181;m, sapphire window for ~0.4 &#181;m &#60; &#955; &#60; 4.2 &#181;m) and 2) able to isolate the furnace chamber thermally. 
			NOTE: The resulting temperatures of the window may influence the window transmission.</li>
			<li>Avoid damage of the IR window. Do not tighten the window to avoid breakage during heat expansion. 
			NOTE: The window material should have a sufficient amount of space to expand when heated up.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Check the resulting field of view (FOV) of the IR camera by examining the thermography image via the IR camera software. Identify the targeted object and its temperature in the thermography image. Adjust the FOV, if necessary.</li>
</ol>
2. Global&#160;customer temperature correction of a fabrication calibrated IR camera
CAUTION: The fabrication of the IR camera is assumed to include a radiometric calibration.
<ol>
	<li>Spot local optical artifacts, such as reflection and background radiation.</li>
	<li>Conduct classic thermocouple measurements of the object while simultaneously recording the wafer including thermocouple with the IR camera.
	<ol>
		<li>Check the validity of the used thermocouples. Search for known characteristic temperature points in the temperature profile of the processed object that can be clearly visibly detected (e.g., disruption in a smooth line). If the thermocouple measures these temperature points correctly, the thermocouple is most likely correctly calibrated.</li>
		<li>Example using silicon solar cells
		<ol>
			<li>Place the thermocouple on the rear aluminum side of the wafer. Take a temperature profile for a standard firing process11.</li>
			<li>Validate the thermocouples by determining whether there is a disruption in the temperature profile from step 2.2.2.1 around the Al-Si eutectic temperature of 577 &#176;C in the form of a flatter curve (as is the case in Figure 2D). 
			NOTE: If the disruption occurs at the temperature around 577 &#176;C, it is a sign that the temperature measurement by the thermocouple is accurate. Use only validated thermocouples for the following steps.</li>
		</ol>
		</li>
		<li>Conduct thermocouple measurements in the temperature range of interest at the same object spot (multiple times for statistical reasons), then at spatially various random spots (for statistical reasons) to obtain time-temperature profiles.</li>
	</ol>
	</li>
	<li>Determine the local uncorrected thermography object temperature underneath the thermocouples from the thermocouple measurements from step 2.2.3 while placing the thermocouple on the upper side of the object.
	<ol>
		<li>Check for a possible local temperature drop around the contacting thermocouple (due to heat dissipation and shading). Assume the temperature in the vicinity of the thermocouple as the object temperature directly under the thermocouple, if a local temperature drop is not present.</li>
		<li>Perform the following steps if a local temperature drop is present.
		<ol>
			<li>Determine the spatial temperature gradient of the present temperature drop in the part that is not covered by the thermocouple. 
			NOTE: It is recommended to determine the gradient at multiple spots around the temperature drop (radially) and determine&#160;an average gradient.</li>
			<li>Estimate the contribution of possible optical artifacts induced by the thermocouple (example protocol for a case in which homogenous temperature along the cell depth direction is assumed, such as in Si solar cells).
			<ol>
				<li>Place the thermocouple on the surface opposite to the measured surface and repeat the thermocouple and thermography measurement in this configuration (as shown in Figure 3A). Turn the object, including the thermocouple, around so that the thermocouple is not in the optical path between the camera and object. 
				NOTE: If the gradient of the local temperature drop is the same for the thermocouple being inside and outside of the optical path (i.e., attached to the measured or opposite surface), it is a sign that the thermocouple most likely does not induce optical artifacts.</li>
				<li>Extrapolate the gradient of the temperature drop in the case of the thermocouple contacting the measured surface (i.e., inside optical path) to the area covered by the thermocouple to obtain the temperature of the object underneath the thermocouple.</li>
				<li>Repeat 2.3.2.2.2 for each measurement from step 2.2.3.</li>
			</ol>
			</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Alternative to 2.3: Determine the local uncorrected thermography object temperature underneath the thermocouples from the thermocouple measurements from step 2.2.3 while placing the thermocouple on the lower side of the object.&#160;To determine the local uncorrected thermography solar cell temperature under the thermocouple, extract the local temperature at the position of the thermocouple.&#160; 
	NOTE: Keeping the thermocouple on the rear&#160;side prevents the thermocouple from blocking the sight on the object&#160;by the camera. Therefore, on the one hand, the temperature correction is significantly simpler. On the other hand, thermocouples are usually not positioned on the lower side of the object&#160;during the firing process, thus might lead to operational complications, which is why this alternative needs to be carried out extra carefully.&#160;</li>
	<li>Correct the uncorrected thermography image with respect to the thermocouple measured temperatures with the data generated from steps 2.3 or 2.4.
	<ol>
		<li>Plot the measured temperatures via thermocouples against the determined temperatures via uncorrected IR thermography. Conduct a curve fitting.</li>
		<li>Apply the obtained curve fit as a general uniform global correction formula for the uncorrected thermography image.</li>
	</ol>
	</li>
	<li>Repeat the temperature correction for each new object type or configuration, especially when the optical parameters differ.</li>
</ol>
3. Evaluation of spatial surface temperature distribution via IR thermography
NOTE: The firing conditions are assumed to be identical for this section.
<ol>
	<li>Creation of a two-dimensional peak temperature distribution map (see Figure 4A)
	<ol>
		<li>Write a script with an appropriate programing language to track the surface object temperature for each object surface spot along the entire camera FOV, i.e. acting as a &#34;virtual thermocouple&#34; placed at all object&#160;spots simultaneously. 
		NOTE: Here, the script is written in MATLAB.</li>
		<li>Extract the maximum value, i.e. the peak temperature, for each object spot and plot these temperatures in a corresponding 2D distribution map.</li>
	</ol>
	</li>
	<li>Average temperature distribution in and perpendicular to the object throughput direction (see Figure 4B)
	<ol>
		<li>In throughput direction: average the 2D temperature distribution in the dimension which is opposite to the throughput direction. What remains, is the average 1D temperature distribution in throughput direction.</li>
		<li>Perpendicular to the throughput direction: average the 2D temperature distribution in the dimension which is in throughput direction. What remains, is the average 1D temperature distribution perpendicular&#160;to the throughput direction. 
		NOTE: It is recommended to leave out the last centimeter (at least) of the edge for the averaging since optical artifacts at the object edge might falsify the resulting temperature average.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Xu, J., Zhang, J., Kuang, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Conveyor Belt Furnace Thermal Processing. , (2018).</li><li>Breitenstein, O., Warta, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Langenkamp Lock-in Thermography: Basics and Use for Evaluating Electronic Devices and Materials. , (2010).</li><li>Ravindra, N. M., Ravindra, K., Mahendra, S., Sopori, B., Fiory, A. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+and+Simulation+of+Emissivity+of+Silicon-Related+Materials+and+Structures.">Modeling and Simulation of Emissivity of Silicon-Related Materials and Structures.</a> Journal of Electronic Materials. 32 (10), 1052-1058 (2003).</li><li>Ourinson, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+Situ+Solar+Wafer+Temperature+Measurement+during+Firing+Process+via+Inline+IR+Thermography.">In Situ Solar Wafer Temperature Measurement during Firing Process via Inline IR Thermography.</a> Physica Status Solidi (RRL) - Rapid Research Letters. 13 (10), 1900270 (2019).</li><li>Ourinson, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In-situ+wafer+temperature+measurement+during+firing+process+via+inline+infrared+thermography.">In-situ wafer temperature measurement during firing process via inline infrared thermography.</a> AIP Conference Proceedings. 2156, 020013 (2019).</li><li>Cooper, I. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+and+Use+of+IR+Belt+Furnace+for+Rapid+Thermal+Firing+of+Screen-Printed+Contacts+to+Si+Solar+Cells.">Understanding and Use of IR Belt Furnace for Rapid Thermal Firing of Screen-Printed Contacts to Si Solar Cells.</a> IEEE Electron Device Letters. 31 (5), 461-463 (2010).</li><li>Schubert, G., Huster, F., Fath, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physical+understanding+of+printed+thick-film+front+contacts+of+crystalline+Si+solar+cells-Review+of+existing+models+and+recent+developments.">Physical understanding of printed thick-film front contacts of crystalline Si solar cells-Review of existing models and recent developments.</a> Solar Energy Materials and Solar Cells. 90 (18-19), 3399-3406 (2006).</li><li>Rauer, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aluminum+Alloying+in+Local+Contact+Areas+on+Dielectrically+Passivated+Rear+Surfaces+of+Silicon+Solar+Cells.">Aluminum Alloying in Local Contact Areas on Dielectrically Passivated Rear Surfaces of Silicon Solar Cells.</a> IEEE Electron Device Letters. 32 (7), 916-918 (2011).</li><li>Pawlik, M., Vilcot, J. -. P., Halbwax, M., Gauthier, M., Le Quang, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+the+firing+step+on+Al+2+O+3+passivation+on+p-type+Czochralski+Si+wafers:+Electrical+and+chemical+approaches.">Impact of the firing step on Al 2 O 3 passivation on p-type Czochralski Si wafers: Electrical and chemical approaches.</a> Japanese Journal of Applied Physics. 54 (8), 21 (2015).</li><li>Lee, B. J., Zhang, Z. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RAD-PRO:+Effective+Software+for+Modeling+Radiative+Properties+in+Rapid+Thermal+Processing.">RAD-PRO: Effective Software for Modeling Radiative Properties in Rapid Thermal Processing.</a> 2005 13th International Conference on Advanced Thermal Processing of Semiconductors. , (2005).</li><li>. Temperature Measurements Available from: <a target="_blank" href="https://meettechniek.info/measuring/temperature.html">https://meettechniek.info/measuring/temperature.html</a> (2020)</li><li>Blakers, A. W., Wang, A., Milne, A. M., Zhao, J., Green, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=22.8%+efficient+silicon+solar+cell.">22.8% efficient silicon solar cell.</a> Applied Physics Letters. 55 (13), 1363-1365 (1989).</li><li>Dullweber, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PERC+:+industrial+PERC+solar+cells+with+rear+Al+grid+enabling+bifaciality+and+reduced+Al+paste+consumption.">PERC+: industrial PERC solar cells with rear Al grid enabling bifaciality and reduced Al paste consumption.</a> Progress in Photovoltaics: Research and Applications. 24 (12), 1487-1498 (2016).</li><li>Ourinson, D., Emanuel, G., Lorenz, A., Clement, F., Glunz, S. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+the+burnout+phase+of+the+contact+firing+process+for+industrial+PERC.">Evaluation of the burnout phase of the contact firing process for industrial PERC.</a> AIP Conference Proceedings. 2147 (1), 040015 (2019).</li></ol>

The authors have nothing to disclose.

Commonly, thermography temperature is corrected via measuring and adapting the optical parameters of the object, transmissive window and path, and environmental temperature of the object and transmissive window2. As an alternative method, a temperature correction technique based on thermocouple measurements is described in this protocol. For the latter method, knowledge of the parameters mentioned above is not required. For the application shown here, this method is sufficient. However, it cannot be guaranteed that the thermocouple method is sufficient for all thermography applications in a conveyor belt furnace.
In the protocol, a uniform global temperature correction of the thermography image is proposed; although, it is more precise to correct the spatially resolved temperature. However, it has been found that the uniform temperature correction is more appropriate in cases of moving objects. Furthermore, it is intended to correct the temperature of the object rather than the surrounding objects (e.g., the belt and walls).
As mentioned in step 2.3.2.2, the example provided here is assumed to have a homogeneous temperature distribution along the object depth. In cases of objects with inhomogeneous temperature distribution along their depths, the temperature on one surface does not resemble the temperature on the opposite surface. Thus, the steps described in section 2.3.2.2&#160;do not apply for these cases. A solution for inhomogeneous temperature distribution along the object depth must be further studied.

Process control and quality assurance of objects processed in conveyor belt furnaces1 is important and accomplished by measuring the surface temperature of the object. Currently, the temperature is typically measured by a thermocouple1. As thermocouple measurements require contact with the object, thermocouples inevitably damage the object. Therefore, it is common to choose representative samples of a batch for temperature measurements, which are not further processed since they become damaged. The measured temperatures of these damaged objects are then generalized to the remaining samples from the batch, which are further processed. Accordingly, production must be interrupted for thermocouple measurements. Furthermore, the contact is local, needs to be readjusted after each measurement, and influences the local temperature.
Infrared (IR) thermography2 has a number of advantages over classic thermocouple measurements and represents a contactless, in-situ, real-time, time-saving, and spatially resolved temperature measurement method. Using this method, each sample of the batch, including those that are further processed, can be measured without interrupting production. In addition, the surface temperature distribution can be measured, which provides insight into temperature homogeneity during the process. The real-time feature allows correction of temperature settings on-the-fly. So far, the possible reasons for not using IR thermography in conveyor belt furnaces are 1) unknown optical parameters of hot objects (especially for nonmetals3) and 2) parasitic environmental radiation in the furnace (i.e., reflected radiation detected by the IR camera in addition to the emitted radiation from the object), which leads to false temperature output2.
Here, as a representative proof-of-concept example of IR thermography in a conveyor belt furnace, we successfully installed an inline thermography system into an IR lamp powered solar firing furnace (Figure 1), which is used during the contact firing process of industrial Si solar cells (Figure 2A,B)4,5. The firing process is a crucial step at the end of industrial solar cell production6. During this step, the contacts of the cell are formed7,8, and surface passivation is activated9. To successfully achieve the latter, the time-temperature profile during the firing process (Figure 2C) must be accurately realized. Therefore, sufficient and efficient temperature control is required. This protocol describes how to install an IR camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and evaluate the spatial surface temperature distribution of a target object.

<table border="0" cellpadding="0" cellspacing="0" style="width:665px;" width="665">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Datalogger incl. Thermal barrier</td>
			<td style="width:121px;">Datapaq Ltd.</td>
			<td style="width:161px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">IR thermography camera &#34;Image IR 8300&#34;</td>
			<td style="width:121px;">InfraTec GmbH</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">IR thermography software &#34;IRBIS Professional 3.1&#34;</td>
			<td style="width:121px;">InfraTec GmbH</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Solar cells</td>
			<td style="width:121px;">Fraunhofer ISE</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Solar firing furnace &#34;RFS 250 Plus&#34;</td>
			<td style="width:121px;">Rehm Thermal Systems GmbH</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sheath thermocouples type K</td>
			<td style="width:121px;">TMH GmbH</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Thermocouple quartzframe</td>
			<td style="width:121px;">Heraeus Noblelight GmbH</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

in situ surface temperature measurement in a conveyor belt furnace via inline infrared thermography

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. Currently, the surface temperature of objects processed in conveyor belt furnaces is typically measured via thermocouples. However, infrared (IR) thermography presents multiple advantages compared to thermocouple measurements, as it is a contactless, real-time, and spatially resolved method. Here, as a representative proof-of-concept example, an inline thermography system is successfully installed into an IR lamp powered solar firing furnace, which is used for the contact firing process of industrial Si solar cells. This protocol describes how to install an IR camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and perform the evaluation of spatial surface temperature distribution on a target object.

As shown in Figure 3B&#8722;D, the example object (here, a silicon solar cell; strictly speaking, a passivated emitter and rear cell [PERC]12; Figure 2A,B) can be clearly detected by the IR camera in different configurations4. The different configurations are monofacially metallized (Figure 3B), bifacially metallized13 (Figure 3C) and nonmetalized PERC samples&#160;(Figure 3D). The difference between the monofacial and bifacial configuration is that the former has a full area aluminum layer, whereas the latter has an H-pattern grid (similar to the silver front side) on the rear side. Here, the IR camera was positioned in a way that the camera FOV captured the peak temperature of the firing process. The peak phase is the most crucial phase during the firing process, since the contacts are actually formed during this phase14. Here, the temperature range of interest resembled the typical peak temperature range of the firing process (i.e., ca. 700&#8211;900 &#176;C1).
For the latter temperature range, the spectral emissivity is quite high and homogenous in the short, middle, and long wavelength infrared spectra3. A double sapphire layer was used as a transmissive window, allowing for good transmission in the short and middle IR wavelength spectra. In order to minimize detection of light from the IR lamps of the furnace (peak wavelength in short wavelength infrared range), an IR camera type with InSb as detector material was chosen, with a detection range of 3.7&#8722;4.1 &#181;m (including filters). Only one-third of the wafer in the throughput direction can be detected at the same time. However, it was sufficient for this work, since the wafer passes the existing field of view entirely.&#160;Naturally, temperature corrected thermography images are shown here. Strictly speaking, the image is temperature-corrected with respect to the solar cells.
As can be seen in Figure 3A, the contacting thermocouple on the opposite side of the optical path caused a temperature drop around itself (with a temperature drop of 10 K), most likely due to heat dissipation and shading. The latter drop is important to estimate the cell temperature during firing without thermocouples, compared to the temperature measured by the thermocouple. Here, the cell was positioned onto a frame when contacted by a thermocouple (Figure 3E). The heat dissipation by the frame caused a temperature drop of around 10 K. Together with the additional heat drop by the thermocouple, the latter measured a 20 K lower temperature than what the cells displayed during standard processing (without the thermocouple equipment). It is important to estimate the latter offset for the used thermocouple system, which is performed with the help of thermography, as shown. The IR camera allows observation of the local heat dissipation of the cells by the conveyor belt if placed directly on the belt (Figure 3F). This is the reason why cells are usually placed on belt elevations to minimize contact between them and the belt.
Figure 4 shows the surface temperature distribution. Since silicon solar cells are typically around 160 &#181;m thick and processed in the furnace for 30 s, it is likely that the temperature distribution along the cell depth is homogenous. Therefore, the results most likely suggest a temperature distribution rather than only a surface temperature distribution. Opposite to the throughput direction, an average temperature gradient of 1 K/cm was obtained. In the throughput direction, the incoming wafer quarter was substantially colder than the trailing wafer rest. The colder incoming portion experienced a gradient of 7 K/cm, while the hotter trailing part experienced a gradient of 0.5 K/cm.
In both directions, the cell edges (the remaining 2 cm) were ignored for determination of the gradients, since the detected temperature at the edges mixed with the colder outside boundary of the cells, resulting in false temperatures. Figure 4C shows a representative 2D temperature distribution of a monofacial solar cell, which was not metallized at the front side. The abovementioned trends in the same and opposite transport directions were observed here, as well. All in all, these results reveal that the solar cells in this work experienced a certain degree of spatial temperature inhomogeneity.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/60963/60963fig1.jpg" /> 
Figure 1: Most important equipment used in the protocol. (A) Lateral scheme of the conveyor belt furnace. This figure panel has been modified from Ourinson et al.4. (B) Zoomed-in last firing zone, visualizing the setup of the thermography system. 1) Furnace wall and isolation, 2) IR camera, 3) IR lamps, 4) insulating window, 5) object transport direction, 6) camera FOV, 7) transportation belt, 8) object, and 9) thermography software. &#160;This figure panel has been modified from Ourinson et al.4. (C) The firing furnace used during this protocol. (D) Image illustrating the used IR camera and transmissive IR window positioned in the firing furnace. The numbers correspond to the numbers from panels A and B. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60963/60963fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/60963/60963fig2.jpg" /> 
Figure 2: Measured objects and their temperatures. (A) Schematic cross-section of a monofacial PERC solar cell. (B) Front (left) and rear (right) side view of an industrial PERC cell. (C) Thermocouple-measured industrial time-temperature profile of a PERC solar cell during the firing process, including segmentation into phases and section, which is covered by the camera field of view. This figure has been modified from Ourinson et al.5. (D) Demonstration of disruption around the eutectic temperature (TEUT) of aluminium and silicon in a firing profile measured by a thermocouple, when the thermocouple is placed on the aluminium rear side of the solar cell. This figure has been modified from Ourinson et al.5. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60963/60963fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/60963/60963fig3.jpg" /> 
Figure 3: Representative temperature-corrected thermography images of PERC solar cells for identical firing conditions. (A) Visible local temperature drop caused by contact of a thermocouple from the rear side. (B) Thermography image of the upper one-third of a monofacially metallized PERC cell, including (1) visible busbars (2) positioned on the visible conveyor belt. TAV shows the average temperature on the wafer. (C) Thermography image of a bifacially metallized PERC cell. (D) Thermography image of a nonmetallized PERC wafer. (E) Thermography image of a wafer placed on a thermocouple frame and contacted by a thermocouple. TTC shows the wafer temperature measured by the thermocouple. (F) Thermography image of a wafer placed directly on the conveyor belt. (G) Color map of the temperature range measured by the IR camera. This figure has been modified from Ourinson et al.5. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60963/60963fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/60963/60963fig4v2.jpg" /> 
Figure 4: Temperature distribution of a PERC solar cell for identical firing conditions. (A) 2D peak temperature distribution of a monofacial PERC solar cell from the front side. (B) Average peak temperature distribution in (right picture) and perpendicular (left picture) to the cell transport direction.&#8221;<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60963/60963fig4v3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography at JoVE.com

In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography

This protocol describes how to install an infrared camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and evaluate the spatial surface temperature distribution of an object of interest. The example objects are industrial silicon solar cells.

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. ...

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Nanyang Technological University

Research

JoVE Journal

Engineering

4.3K Views.  Fraunhofer Institute for Solar Energy Systems ISE. This protocol describes how to install an infrared camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and evaluate the spatial surface temperature distribution of an object of interest. The example objects are industrial silicon solar cells.

Video: In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography

In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation

Supercontinuum generation (SCG) in a tapered chalcogenide fiber is desirable for broadening mid-infrared (or mid-IR, roughly the 2-20 &mu;m wavelength range) frequency combs1, 2 for applications such as molecular fingerprinting, 3 trace gas detection, 4 laser-driven particle acceleration, 5 and x-ray production via high harmonic generation. 6 Achieving efficient SCG in a tapered optical fiber requires precise control of the group velocity dispersion (GVD) and the temporal properties of the optical pulses at the beginning of the fiber, 7 which depend strongly on the geometry of the taper. 8 Due to variations in the tapering setup and procedure for successive SCG experiments-such as fiber length, tapering environment temperature, or power coupled into the fiber, in-situ spectral monitoring of the SCG is necessary to optimize the output spectrum for a single experiment.
	In-situ fiber tapering for SCG consists of coupling the pump source through the fiber to be tapered to a spectral measurement device. The fiber is then tapered while the spectral measurement signal is observed in real-time. When the signal reaches its peak, the tapering is stopped. The in-situ tapering procedure allows for generation of a stable, octave-spanning, mid-IR frequency comb from the sub harmonic of a commercially available near-IR frequency comb. 9 This method lowers cost due to the reduction in time and materials required to fabricate an optimal taper with a waist length of only 2 mm.
	The in-situ tapering technique can be extended to optimizing microstructured optical fiber (MOF) for SCG10 or tuning of the passband of MOFs, 11 optimizing tapered fiber pairs for fused fiber couplers12 and wavelength division multiplexers (WDMs), 13 or modifying dispersion compensation for compression or stretching of optical pulses.14-16

In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation

We describe a method for in-situ tapering of As2S3 fibers to achieve efficient mid-infrared supercontinuum generation. By tapering while monitoring the supercontinuum&#x2019;s spectrum, the spectral width can be maximized for a fiber taper. In-situ fiber tapering can be applied to optimize the performance of other fiber-based devices.

Supercontinuum  generation (SCG) in a tapered chalcogenide fiber is desirable for broadening mid-infrared  (or mid-IR, roughly the 2-20 &mu;m wavelength ...

Fabrication and Operation of a Nano-Optical Conveyor Belt

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological and physical sciences over the past few decades. The progress made in this field invites further study of even smaller systems and at a larger scale, with tools that could be distributed more easily and made more widely available. Unfortunately, the fundamental laws of diffraction limit the minimum size of the focal spot of a laser beam, which makes particles smaller than a half-wavelength in diameter hard to trap and generally prevents an operator from discriminating between particles which are closer together than one half-wavelength. This precludes the optical manipulation of many closely-spaced nanoparticles and&#160;limits the&#160;resolution of optical-mechanical systems. Furthermore, manipulation using focused beams requires beam-forming or steering optics, which can be very bulky and expensive. To address these limitations in the system scalability of conventional optical trapping our lab has devised an alternative technique which utilizes near-field optics to move particles across a chip. Instead of focusing laser beams in the far-field, the optical near field of plasmonic resonators produces the necessary local optical intensity enhancement to overcome the restrictions of diffraction and manipulate particles at higher resolution. Closely-spaced resonators produce strong optical traps which can be addressed to mediate the hand-off of particles from one to the next in a conveyor-belt-like fashion. Here, we describe how to design and produce a conveyor belt using a gold surface patterned with plasmonic C-shaped resonators and how to operate it with polarized laser light to achieve super-resolution nanoparticle manipulation and transport. The nano-optical conveyor belt chip can be produced using lithography techniques and easily packaged and distributed.

The scalability and resolution of conventional optical manipulation techniques are limited by diffraction. We circumvent the diffraction limit and describe a method of optically transporting nanoparticles across a chip using a gold surface patterned with a path of closely spaced C-shaped plasmonic resonators.

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological ...

Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film synthesis) for the purpose of exploratory materials research. Certain materials pose a challenge wherein the traditional bulk Hall bar device fabrication method is insufficient to produce a measureable device for sample transport measurement, principally because the single crystal size is too small to attach wire leads to the sample in a Hall bar configuration. This can be, for example, because the first batch of a new material synthesized yields very small single crystals or because flakes of samples of one to very few monolayers are desired. In order to enable rapid characterization of materials that may be carried out in parallel with improvements to their growth methodology, a method of device fabrication for very small samples has been devised to permit the characterization of novel materials as soon as a preliminary batch has been produced. A slight variation of this methodology is applicable to producing devices using exfoliated samples of two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDs), as well as multilayer heterostructures of such materials. Here we present detailed protocols for the experimental device fabrication of fragments and flakes of novel materials with micron-sized dimensions onto substrate and subsequent measurement in a commercial superconducting magnet, dry helium close-cycle cryostat magnetotransport system at temperatures down to 0.300 K and magnetic fields up to 12 T.

We describe the methodology of mechanical exfoliation and deposition of flakes of novel materials with micron-sized dimensions onto substrate, fabrication of experimental device structures for transport experimentation, and the magnetotransport measurement in a dry helium close-cycle cryostat at temperatures down to 0.300 K and magnetic fields up to 12 T.

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film ...

The Measurement of Unsteady Surface Pressure Using a Remote Microphone Probe

Microphones are widely applied to measure pressure fluctuations at the walls of solid bodies immersed in turbulent flows. Turbulent motions with various characteristic length scales can result in pressure fluctuations over a wide frequency range. This property of turbulence requires sensing devices to have sufficient sensitivity over a wide range of frequencies. Furthermore, the small characteristic length scales of turbulent structures require small sensing areas and the ability to place the sensors in very close proximity to each other. The complex geometries of the solid bodies, often including large surface curvatures or discontinuities, require the probe to have the ability to be set up in very limited spaces. The development of a remote microphone probe, which is inexpensive, consistent, and repeatable, is described in the present communication. It allows for the measurement of pressure fluctuations with high spatial resolution and dynamic response over a wide range of frequencies. The probe is small enough to be placed within the interior of typical wind tunnel models. The remote microphone probe includes a small, rigid, and hollow tube that penetrates the model surface to form the sensing area. This tube is connected to a standard microphone, at some distance away from the surface, using a "T" junction. An experimental method is introduced to determine the dynamic response of the remote microphone probe. In addition, an analytical method for determining the dynamic response is described. The analytical method can be applied in the design stage to determine the dimensions and properties of the RMP components.

Here, we present a protocol to measure, with high spatial resolution, the unsteady surface pressure in turbulent flows. This method demonstrates the construction of a remote microphone probe (RMP) and the determination of its frequency-dependent, complex transfer function. An analytical determination of the dynamic response is presented and validated.

Microphones are widely applied to measure pressure fluctuations at the walls of solid bodies immersed in turbulent flows. Turbulent motions with various ...

Optical Trap Loading of Dielectric Microparticles In Air

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly scattered dielectric microparticles adhered to a glass substrate are momentarily detached using ultrasonic vibrations generated by a piezoelectric transducer (PZT). Then, the optical beam focused on a selected particle lifts it up to the optical trap while the vibrationally excited microparticles fall back to the substrate. A particle may be trapped at the nominal focus of the trapping beam or at a position above the focus (referred to here as the levitation position) where gravity provides the restoring force. After the measurement, the trapped particle can be placed at a desired position on the substrate in a controlled manner. 
In this protocol, an experimental procedure for selective optical trap loading in air is outlined. First, the experimental setup is briefly introduced. Second, the design and fabrication of a PZT holder and a sample enclosure are illustrated in detail. The optical trap loading of a selected microparticle is then demonstrated with step-by-step instructions including sample preparation, launching into the trap, and use of electrostatic force to excite particle motion in the trap and measure charge. Finally, we present recorded particle trajectories of Brownian and ballistic motions of a trapped microparticle in air. These trajectories can be used to measure stiffness or to verify optical alignment through time domain and frequency domain analysis. Selective trap loading enables optical tweezers to track a particle and its changes over repeated trap loadings in a reversible manner, thereby enabling studies of particle-surface interaction.

A protocol for launching and stably trapping selected dielectric microparticles in air is presented.

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly ...

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.

A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented here.

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials ...

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) scaffolds with tunable specific surface areas up to 80 m2&#183;g-1. An aqueous solution of a zirconium salt, yttrium salt, and glucose is mixed with propylene oxide (PO) to form a gel. The gel is dried under ambient conditions to form a xerogel. The xerogel is pressed into pellets and then sintered in an argon atmosphere. During sintering, a YSZ ceramic phase forms and the organic components decompose, leaving behind amorphous carbon. The carbon formed in situ serves as a hard template, preserving a high surface area YSZ nanomorphology at sintering temperature. The carbon is subsequently removed by oxidation in air at low temperature, resulting in a porous, nanostructured YSZ scaffold. The concentration of the carbon template and the final scaffold surface area can be systematically tuned by varying the glucose concentration in the gel synthesis. The carbon template concentration was quantified using thermogravimetric analysis (TGA), the surface area and pore size distribution was determined by physical adsorption measurements, and the morphology was characterized using scanning electron microscopy (SEM). Phase purity and crystallite size was determined using X-ray diffraction (XRD). This fabrication approach provides a novel, flexible platform for realizing unprecedented scaffold surface areas and nanomorphologies for ceramic-based electrochemical energy conversion applications, e.g. solid oxide fuel cell (SOFC) electrodes.

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels

A protocol for fabricating porous, nanostructured yttria-stabilized-zirconia (YSZ) scaffolds at temperatures between 1,000 &#176;C and 1,400 &#176;C is presented.

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) ...

Preparation and High-temperature Anti-adhesion Behavior of a Slippery Surface on Stainless Steel

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A typical anti-wetting superhydrophobic surface easily fails when exposed to a high-temperature liquid. Recently, Nepenthes-inspired slippery surfaces demonstrated a new way to solve the adhesion problem. A lubricant layer on the slippery surface can act as a barrier between the repelled materials and the surface structure. However, the slippery surfaces in previous studies rarely showed high-temperature resistance. Here, we describe a protocol for the preparation of slippery surfaces with high-temperature resistance. A photolithography-assisted method was used to fabricate pillar structures on stainless steel. By functionalizing the surface with saline, a slippery surface was prepared by adding silicone oil. The prepared slippery surface maintained the anti-wetting property for water, even when the surface was heated to 300 &#176;C. Also, the slippery surface exhibited great anti-adhesion effects on soft tissues at high temperatures. This type of slippery surface on stainless steel has applications in medical devices, mechanical equipment, etc.

Slippery surfaces provide a new way to solve the adhesion problem. This protocol describes how to fabricate slippery surfaces at high temperatures. The results demonstrate that the slippery surfaces showed anti-wetting for liquids and a remarkable anti-adhesion effect on soft tissues at high temperatures.

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A ...

Generation of Size-controlled Poly (ethylene Glycol) Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. This paper proposes a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation. The polydimethylsiloxane (PDMS) chip was fabricated using the multi-layer soft lithography method. Hexadecane containing surfactant was used as the continuous phase, and PEGDA with the ultraviolet (UV) photo-initiator was the dispersed phase. Surfactants allowed the local surface tension to drop and formed a more cusped tip which promoted breaking into tiny micro-droplets. As the pressure of dispersed phase was constant, the size of droplets became smaller with increasing continuous phase pressure before dispersed phase flow was broken off. As a result, droplets with size variation from 1 &#181;m to 80 &#181;m in diameter could be selectively achieved by changing the pressure ratio in two inlet channels, and the average coefficient of variation was estimated to be below 7%. Furthermore, droplets could turn into micro-beads by UV exposure for photo-polymerization. Conjugating biomolecules on such micro-beads surface have many potential applications in the fields of biology and chemistry.

Generation of Size-controlled Poly ethylene Glycol Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Here, we present a protocol to illustrate the fabrication processes and verifying experiments of a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation.

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. ...

Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere

A technique to measure the temperature of water and non-turbid aqueous media surrounding an induction-heated small magnetic sphere is presented. This technique utilizes wavelengths of 1150 and 1412 nm, at which the absorption coefficient of water is dependent on temperature. Water or a non-turbid aqueous gel containing a 2.0-mm- or 0.5-mm-diameter magnetic sphere is irradiated with 1150 nm or 1412 nm incident light, as selected using a narrow bandpass filter; additionally, two-dimensional absorbance images, which are the transverse projections of the absorption coefficient, are acquired via a near-infrared camera. When the three-dimensional distributions of temperature can be assumed to be spherically symmetric, they are estimated by applying inverse Abel transforms to the absorbance profiles. The temperatures were observed to consistently change according to time and the induction heating power.

A technique utilizing wavelengths of 1150 and 1412 nm to measure the temperature of water surrounding an induction-heated small magnetic sphere is presented.

A technique to measure the temperature of water and non-turbid aqueous media surrounding an induction-heated small magnetic sphere is presented. This ...

In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography

Summary

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Chapters in this video

In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation

Fabrication and Operation of a Nano-Optical Conveyor Belt

Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials

The Measurement of Unsteady Surface Pressure Using a Remote Microphone Probe

Optical Trap Loading of Dielectric Microparticles In Air

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

Preparation and High-temperature Anti-adhesion Behavior of a Slippery Surface on Stainless Steel

Generation of Size-controlled Poly (ethylene Glycol) Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere