The authors would like to thank Professor W.S. Sampath for use of his deposition systems, Kevan Cameron for system support, Dr. Amit Munshi for his work with thicker bilayer cells and supplemental footage of the in-line automated CSS vacuum deposition system, and Dr. Darius Kuciauskas for assistance with TRPL measurements. This material is based upon work supported by the U.S. Department of Energy&#8217;s Office of Energy Efficiency and Renewable Energy (EERE) under Solar Energy Technologies Office (SETO) Agreement Number DE-EE0007543.

<ol>
	<li>. Global energy demand rose by 2.3% in 2018, its fastest pace in the last decade Available from: <a target="_blank" href="https://www.iea.org/newsroom/news/2019/march/global-energy-demand-rose-by-23-in-2018-its-fastest-pace-in-the-last-decade.html">https://www.iea.org/newsroom/news/2019/march/global-energy-demand-rose-by-23-in-2018-its-fastest-pace-in-the-last-decade.html</a> (2019)</li><li>Morton, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solar+energy:+A+new+day+dawning?:+Silicon+valley+sunrise.">Solar energy: A new day dawning?: Silicon valley sunrise.</a> Nature. 443 (7107), 19-22 (2006).</li><li>. Best research-cell efficiency chart Available from: <a target="_blank" href="https://www.nrel.gov/pv/cell-efficiency.html">https://www.nrel.gov/pv/cell-efficiency.html</a> (2019)</li><li>Munshi, A., 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=Polycrystalline+CdSeTe/CdTe+absorber+cells+with+28+mA/cm2+short-circuit+current.">Polycrystalline CdSeTe/CdTe absorber cells with 28 mA/cm2 short-circuit current.</a> IEEE Journal of Photovoltaics. 8 (1), 310-314 (2018).</li><li>Metzger, W. K., 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=Exceeding+20%+efficiency+with+in+situ+group+V+doping+in+polycrystalline+CdTe+solar+cells.">Exceeding 20% efficiency with in situ group V doping in polycrystalline CdTe solar cells.</a> Nature Energy. 4, 837-845 (2019).</li><li>Hsiao, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electroplated+CdTe+solar+technology+at+Reel+Solar.">Electroplated CdTe solar technology at Reel Solar.</a> Proceedings of 46thIEEE PVSC. , (2019).</li><li>Bothwell, A. M., Drayton, J. A., Jundt, P. M., Sites, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+thin+CdTe+solar+cells+with+a+CdSeTe+front+layer.">Characterization of thin CdTe solar cells with a CdSeTe front layer.</a> MRS Advances. 4 (37), 2053-2062 (2019).</li><li>Fiducia, T. A. 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=Understanding+the+role+of+selenium+in+defect+passivation+for+highly+efficient+selenium-alloyed+cadmium+telluride+solar+cells.">Understanding the role of selenium in defect passivation for highly efficient selenium-alloyed cadmium telluride solar cells.</a> Nature Energy. 4, 504-511 (2019).</li><li>Swanson, D. E., 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=Single+vacuum+chamber+with+multiple+close+space+sublimation+sources+to+fabricate+CdTe+solar+cells.">Single vacuum chamber with multiple close space sublimation sources to fabricate CdTe solar cells.</a> Journal of Vacuum Science and Technology A. 34, 021202 (2016).</li><li>McCandless, B. E., Sites, J. R., Luque, A., Hegedus, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cadmium+telluride+solar+cells.">Cadmium telluride solar cells.</a> Handbook of Photovoltaic Science and Engineering. , 617-662 (2003).</li><li>Abbas, A., 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=Cadmium+chloride+assisted+re-crystallization+of+CdTe:+the+effect+of+annealing+over-treatment.">Cadmium chloride assisted re-crystallization of CdTe: the effect of annealing over-treatment.</a> Proceedings of 40th IEEE PVSC. , (2014).</li><li>Munshi, A., 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=Effect+of+varying+process+parameters+on+CdTe+thin+film+device+performance+and+its+relationship+to+film+microstructure.">Effect of varying process parameters on CdTe thin film device performance and its relationship to film microstructure.</a> Proceedings of 40th IEEE PVSC. , (2014).</li><li>Metzger, W. K., 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=Time-resolved+photoluminescence+studies+of+CdTe+solar+cells.">Time-resolved photoluminescence studies of CdTe solar cells.</a> Journal of Applied Physics. 94 (5), 3549-3555 (2003).</li><li>Moseley, J., 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=Luminescence+methodology+to+determine+grain-boundary,+grain-interior,+and+surface+recombination+in+thin+film+solar+cells.">Luminescence methodology to determine grain-boundary, grain-interior, and surface recombination in thin film solar cells.</a> Journal of Applied Physics. 124, 113104 (2018).</li><li>Amarasinghe, 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=Obtaining+large+columnar+CdTe+grains+and+long+lifetime+on+nanocrystalline+CdSe,+MgZnO,+or+CdS+layers.">Obtaining large columnar CdTe grains and long lifetime on nanocrystalline CdSe, MgZnO, or CdS layers.</a> Advanced Energy Materials. 8, 1702666 (2018).</li><li>Tencor Instruments. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Alpha-Step 100 User's Manual. , (1984).</li><li>Wojtowicz, A., Huss, A. M., Drayton, J. A., Sites, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+CdCl2+passivation+on+thin+CdTe+absorbers+fabricated+by+close-space+sublimation.">Effects of CdCl2 passivation on thin CdTe absorbers fabricated by close-space sublimation.</a> Proceedings of 44th IEEE PVSC. , (2017).</li><li>Kirchartz, T., Ding, K., Rau, U., Abou-Ras, D., Kirchartz, T., Rau, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fundamental+electrical+characterization+of+thin+film+solar+cells.">Fundamental electrical characterization of thin film solar cells.</a> Advanced Characterization Techniques for Thin Film Solar Cells. , 47 (2011).</li><li>Swanson, D. E., Sites, J. R., Sampath, W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Co-sublimation+of+CdSexTe1-x+layers+for+CdTe+solar+cells.">Co-sublimation of CdSexTe1-x layers for CdTe solar cells.</a> Solar Energy Materials &amp; Solar Cells. 159, 389-394 (2017).</li><li>McCandless, B. E., 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=Overcoming+Carrier+Concentration+Limits+in+Polycrystalline+CdTe+Thin+Films+with+In+Situ+Doping.">Overcoming Carrier Concentration Limits in Polycrystalline CdTe Thin Films with In Situ Doping.</a> Scientific Reports. 8, 14519 (2018).</li><li>Romeo, N., Bossio, A., Rosa, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+back+contact+in+CdTe/CdS+thin+film+solar+cells.">The back contact in CdTe/CdS thin film solar cells.</a> Proceedings ISES Solar World Congress 2017. , (2017).</li><li>Munshi, A. H., 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=Doping+CdSexTe1-x/CdTe+graded+absorber+films+with+arsenic+for+thin+film+photovoltaics.">Doping CdSexTe1-x/CdTe graded absorber films with arsenic for thin film photovoltaics.</a> Proceedings of 46th IEEE PVSC. , (2019).</li><li>Danielson, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Doping+CdTe+Absorber+Cells+using+Group+V+Elements.">Doping CdTe Absorber Cells using Group V Elements.</a> Proceedings of WCPEC-7. , (2018).</li><li>Hsiao, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Electron Reflector Strategy for CdTe Thin film Solar Cells. , (2010).</li><li>Swanson, D. E., 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=Incorporation+of+Cd1-xMgxTe+as+an+electron+reflector+for+cadmium+telluride+photovoltaic+cells.">Incorporation of Cd1-xMgxTe as an electron reflector for cadmium telluride photovoltaic cells.</a> Proceedings of MRS Spring Meeting and Exhibit. , (2015).</li><li>Wendt, R., Fischer, A., Grecu, D., Compaan, A. 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The authors have nothing to disclose.

Thin bilayer CdSeTe/CdTe photovoltaic devices demonstrate improvements in efficiency compared to their CdTe counterparts because of better material quality and increased current collection. Such enhanced efficiencies have been demonstrated in bilayer absorbers greater than 3 &#956;m5,7, and now with optimized fabrication conditions, it has been demonstrated that increased efficiencies are also achievable for thinner, 1.5-&#956;m bilayer absorbers.
<p class="j...

Global energy demand is quickly accelerating, and the year 2018 demonstrated the fastest( 2.3%) growth rate in the last decade1. Paired with increasing awareness of the effects of climate change and the burning of fossil fuels, the need for cost-competitive, clean, and renewable energy has become abundantly clear. Of the many renewable energy sources, solar energy is distinctive for its total potential, as the amount of solar energy that reaches earth far exceeds global energy consumption2.
Photovoltaic (PV) devices directly convert solar energy to electrical power and are versatile in scalability (e.g., personal use mini-modules and grid-integrated solar arrays) and material technologies. Technologies such as multi- and single-junction, single-crystal gallium arsenide (GaAs) solar cells have efficiencies reaching 39.2% and 35.5%, respectively3. However, fabrication of these high efficiency solar cells is costly and time-consuming. Polycrystalline cadmium telluride (CdTe) as a material for thin film PVs is advantageous for its low cost, high-throughput fabrication, variety of deposition techniques, and favorable absorption coefficient. These attributes make CdTe propitious for large- scale manufacturing, and improvements in efficiency have made CdTe cost-competitive with PV-market-dominant silicon and fossil fuels4.
One recent advancement that has driven the increase in CdTe device efficiency is the incorporation of cadmium selenium telluride (CdSeTe) alloy material into the absorber layer. Integrating the lower ~1.4 eV band gap CdSeTe material into a 1.5 eV CdTe absorber reduces the front band gap of the bilayer absorber. This increases the photon fraction above the band gap and thus improves current collection. Successful incorporation of CdSeTe into absorbers that are 3 &#956;m or thicker for increased current density has been demonstrated with various fabrication techniques (i.e., close-space sublimation, vapor transport deposition, and electroplating)5,6,7. Increased room temperature photoluminescence emission spectroscopy (PL), time-resolved photoluminescence (TRPL), and electroluminescence signals from bilayer absorber devices5,8 indicate that in addition to increased current collection, the CdSeTe appears to have better radiative efficiency and minority carrier lifetime, and a CdSeTe/CdTe device has a larger voltage relative to the ideal than with CdTe only. This has largely been attributed to selenium passivation of bulk defects9.
Little research has been reported on the incorporation of CdSeTe into thinner (&#8804;1.5 &#956;m) CdTe absorbers. We have therefore investigated the characteristics of thin 0.5 &#956;m CdSeTe/1.0 &#956;m CdTe bilayer-absorber devices fabricated by close-space sublimation (CSS) to determine whether the benefits seen in thick bilayer absorbers are also attainable with thin bilayer absorbers. Such CdSeTe/CdTe absorbers, more than twice as thin as their thicker counterparts, offer a notable decrease in deposition time and material and lower manufacturing costs. Finally, they hold potential for future device architecture developments which require absorber thicknesses of less than 2 &#956;m.
CSS deposition of absorbers in a single automated in-line vacuum system offers many advantages over other fabrication methods10,11. Faster deposition rates with CSS fabrication boosts device throughput and promotes larger experimental datasets. Additionally, the single vacuum environment of the CSS system in this work limits potential challenges with absorber interfaces. Thin-film PV devices have many interfaces, each of which can act as a recombination center for electrons and holes, thus reducing the overall device efficiency. The use of a single vacuum system for the CdSeTe, CdTe, and cadmium chloride (CdCl2) depositions (necessary for good absorber quality12,13,14,15,16) can produce a better interface and reduce interfacial defects.
The in-line automated vacuum system developed at Colorado State University10 is also advantageous in its scalability and repeatability. For example, deposition parameters are user-set, and the deposition process is automated such that the user does not need to make adjustments during absorber fabrication. Although small area research devices are fabricated in this system, the system design can be scaled up for larger area depositions, enabling a link between research-scale experimentation and module-scale implementation.
This protocol presents the fabrication methods used to manufacture 0.5-&#956;m CdSeTe/1.0-&#956;m CdTe thin-film PV devices. For comparison, a set of 1.5 &#956;m CdTe devices are fabricated. Single and bilayer absorber structures have nominally identical deposition conditions in all process steps, excluding the CdSeTe deposition. To characterize whether thin CdSeTe/CdTe absorbers retain the same benefits demonstrated by their thicker counterparts, current density-voltage (J-V), quantum efficiency (QE), and PL measurements are performed on the thin single and bilayer absorber devices. An increase in short-circuit current density (JSC) as measured by J-V and QE, in addition to an increase in PL signal for the CdSeTe/CdTe vs. CdTe device, indicate that thin CdSeTe/CdTe devices fabricated by CSS show notable improvement in current collection, material quality, and device efficiency.
Although this work focuses on the benefits associated with the incorporation of a CdSeTe alloy into a CdTe PV device structure, the complete fabrication process for CdTe and CdSeTe/CdTe devices is described subsequently in full. Figure 1A,B shows completed device structures for CdTe and CdSeTe/CdTe devices respectively, comprised of a transparent conducting oxide (TCO)-coated glass substrate, n-type magnesium zinc oxide (MgZnO) emitter layer, p-type CdTe or CdSeTe/CdTe absorber with CdCl2 treatment and copper doping treatment, thin Te layer, and nickel back contact. Excluding the CSS absorber deposition, the fabrication conditions are identical between the single and bilayer structure. Thus, unless otherwise noted, each step is performed on both CdTe and CdSeTe/CdTe structures.

<table border="0" cellpadding="0" cellspacing="0" style="width:572px;" width="573">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Alpha Step Surface Profilometer</td>
			<td style="width:71px;">Tencor Instruments</td>
			<td style="width:119px;">10-00020</td>
			<td style="width:167px;">Instrument for measuring film thickness</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">CdCl2 Material</td>
			<td style="width:71px;">5N Plus</td>
			<td style="width:119px;">N/A</td>
			<td>Material for absorber passivation treatment</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">CdSeTe Semiconductor Material</td>
			<td style="width:71px;">5N Plus</td>
			<td style="width:119px;">N/A</td>
			<td>P-type semiconductor material for absorber layer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">CdTe Semiconductor Material</td>
			<td style="width:71px;">5N Plus</td>
			<td style="width:119px;">N/A</td>
			<td>P-type semiconductor material for absorber layer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">CESAR RF Power Generator</td>
			<td style="width:71px;">Advanced Energy</td>
			<td style="width:119px;">61300050</td>
			<td>Power generator for MgZnO sputter deposition</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">CuCl Material</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:119px;">N/A</td>
			<td>Material for absorber doping</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Delineation Material</td>
			<td style="width:71px;">Kramer Industries Inc.</td>
			<td style="width:119px;">Melamine Type 3 60-80 mesh</td>
			<td>Plastic beading material for film delineation</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Glovebox Enclosure</td>
			<td style="width:71px;">Vaniman Manufacturing Co.</td>
			<td style="width:119px;">Problast 3</td>
			<td>Glovebox enclosure for film delineation</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Gold Crystal</td>
			<td style="width:71px;">Kurt J. Lesker Company</td>
			<td>KJLCRYSTAL6-G10</td>
			<td>Crystal for Te evaporation thickness monitor</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">HVLP and Standard Gravity Feed Spray Gun Kit</td>
			<td style="width:71px;">Husky</td>
			<td style="width:119px;">HDK00600SG</td>
			<td>Applicator spray gun for Ni paint back contact application</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">MgZnO Sputter Target</td>
			<td style="width:71px;">Plasmaterials, Inc.</td>
			<td style="width:119px;">PLA285287489</td>
			<td>N-type emitter layer material</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Micro 90 Glass Cleaning Solution</td>
			<td style="width:71px;">Cole-Parmer</td>
			<td>EW-18100-05</td>
			<td>Solution for initial glass cleaning</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">NSG Tec10 Substrates</td>
			<td style="width:71px;">Pilkington</td>
			<td style="width:119px;">N/A</td>
			<td>Transparent-conducting oxide glass for front electrical contact</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Super Shield Ni Conductive Coating</td>
			<td style="width:71px;">MG Chemicals</td>
			<td style="width:119px;">841AR-3.78L</td>
			<td>Conductive paint for back contact layer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Te Material</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:119px;">MKBZ5843V</td>
			<td>Material for back contact layer</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Thickness Monitor</td>
			<td style="width:71px;">R.D. Mathis Company</td>
			<td style="width:119px;">TM-100</td>
			<td>Instrument for programming and monitoring Te evaporation conditions</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Thinner 1</td>
			<td style="width:71px;">MG Chemicals</td>
			<td style="width:119px;">4351-1L</td>
			<td>Paint thinner to mix with Ni for back contact layer</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Ultrasonic Cleaner 1</td>
			<td style="width:71px;">L &#38; R Electronics</td>
			<td style="width:119px;">Q28OH</td>
			<td>Ultrasonic cleaner 1 for glass cleaning</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Ultrasonic Cleaner 2</td>
			<td style="width:71px;">Ultrasonic Clean</td>
			<td style="width:119px;">100S</td>
			<td>Ultrasonic cleaner 2 for glass cleaning</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">UV/VIS Lambda 2 Spectrometer</td>
			<td style="width:71px;">PerkinElmer</td>
			<td style="width:119px;">166351</td>
			<td>Spectrometer used for transmission measurements on CdSeTe films</td>
		</tr>
	</tbody>
</table>

close-space sublimation-deposited ultra-thin cdsete/cdte solar cells for enhanced short-circuit current density and photoluminescence

Developments in photovoltaic device architectures are necessary to make solar energy a cost-effective and reliable source of renewable energy amidst growing global energy demands and climate change. Thin film CdTe technology has demonstrated cost-competitiveness and increasing efficiencies due partially to rapid fabrication times, minimal material usage, and introduction of a CdSeTe alloy into a ~3 &#956;m absorber layer. This work presents the close-space sublimation fabrication of thin, 1.5 &#181;m CdSeTe/CdTe bilayer devices using an automated in-line vacuum deposition system. The thin bilayer structure and fabrication technique minimize deposition time, increase device efficiency, and facilitate future thin absorber-based device architecture development. Three fabrication parameters appear to be the most impactful for optimizing thin CdSeTe/CdTe absorber devices: substrate preheat temperature, CdSeTe:CdTe thickness ratio, and CdCl2 passivation. For proper sublimation of the CdSeTe, the substrate temperature prior to deposition must be ~540 &#176;C (higher than that for CdTe) as controlled by dwell time in a preheat source. Variation in the CdSeTe:CdTe thickness ratio reveals a strong dependence of device performance on this ratio. The optimal absorber thicknesses are 0.5 &#956;m CdSeTe/1.0 &#956;m CdTe, and non-optimized thickness ratios reduce efficiency through back-barrier effects. Thin absorbers are sensitive to CdCl2 passivation variation; a much less aggressive CdCl2 treatment (compared to thicker absorbers) regarding both temperature and time yields optimal device performance. With optimized fabrication conditions, CdSeTe/CdTe increases device short-circuit current density and photoluminescence intensity compared to single-absorber CdTe. Additionally, an in-line close-space sublimation vacuum deposition system offers material and time reduction, scalability, and attainability of future ultra-thin absorber architectures.

The addition of CdSeTe to a thin CdTe absorber improves device efficiency through superior absorber material quality and higher short-circuit current density (JSC). Figure 3A and Figure 3B, (adapted from Bothwell et al.8) show PL and TRPL, respectively, for the single CdTe absorber and CdSeTe/CdTe bilayer absorber devices. Both PL and TRPL measurements clearly show improved photoluminescence with the CdSeTe/CdTe bilayer absorbe...

Watch this Scientific Journal Video about Close-Space Sublimation-Deposited Ultra-Thin CdSeTe/CdTe Solar Cells for Enhanced Short-Circuit Current Density and Photoluminescence at JoVE.com

Close-Space Sublimation-Deposited Ultra-Thin CdSeTe/CdTe Solar Cells for Enhanced Short-Circuit Current Density and Photoluminescence

This work describes the complete fabrication process of thin absorber cadmium selenium telluride/cadmium telluride photovoltaic devices for enhanced efficiency. The process utilizes an automated in-line vacuum system for close-space sublimation deposition that is scalable, from fabrication of small area research devices as well as large-scale modules.

Developments in photovoltaic device architectures are necessary to make solar energy a cost-effective and reliable source of renewable energy amidst ...

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8.0K Views.  Colorado State University. This work describes the complete fabrication process of thin absorber cadmium selenium telluride/cadmium telluride photovoltaic devices for enhanced efficiency. The process utilizes an automated in-line vacuum system for close-space sublimation deposition that is scalable, from fabrication of small area research devices as well as large-scale modules.