In this paper, interface engineering via sputtering of CdO nanolayer at the buffer-CdS/CdTe-absorber interface is demonstrated as an efficient approach to improve the performance of solar cell device. The i-CdO interfacial layer with various thicknesses from 5 nm to 35 nm was deposited by DC magnetron sputtering. Comparative studies on TCO/CdS/CdTe and TCO/CdS/CdO/CdTe interfaces have been conducted by current-voltage, capacitance-voltage and admittance spectroscopy measurements. The current-voltage characteristics of the devices with an area of 0.45 cm 2 under 100 mW/cm 2 illumination, at the optimum thickness of CdO intermediate layer in the proposed structures, show increases of the short circuit current density and the open circuit voltage by 5% and 25%, respectively. The efficiency improvement of 3.1% of p-i-n cell over p-n cell is observed. Results of the temperature-dependent current-voltage and admittance measurements revealed the removing of the deep level defect with the activation energy of 0.43 eV and the reducing of the ideality factor from 1.9 to 1.8 via buffer/absorber interfacial passivation method. Interface passivation appears to be critical to improve the short circuit current density and the open circuit voltage, and CdO thin film is clearly effective for this purpose.
Zghaibeh, M., Okonkwo, P.C., et al. (2022) CdTe Solar Cells Fabrication and Examination Techniques: A Focused Review. International Journal of Green Energy, 20, 555-570. https://doi.org/10.1080/15435075.2022.2126943
Romeo, A. and Artegiani, E. (2021) CdTe-Based Thin Film Solar Cells: Past, Present and Future. Energies, 14, Article 1684. https://doi.org/10.3390/en14061684
Bonnet, D. (1992) The CdTe Thin Film Solar Cell—An Overview. International Journal of Solar Energy, 12, 914-924. https://doi.org/10.1080/01425919208909746
Britt, J. and Ferekides, C. (1993) Thin-Film CdS/CdTe Solar Cell with 15.8% Efficiency. Applied Physics Letters, 62, Article ID: 2851. https://doi.org/10.1063/1.109629
Wu, X. (2004) High-Efficiency Polycrystalline CdTe Thin-Film Solar Cells. Solar Energy, 77, 803-814. https://doi.org/10.1016/j.solener.2004.06.006
Wu, X., Dhere, R., Albin, D. and Gessert, T. (2001) Advances in CdTe R&D at NREL. Proceedings of the NCPV Program Review Meeting, Colorado, 14-17 October 2001, 47.
Gloeckler, M., Sankin, I. and Zhao, Z. (2013) CdTe Solar Cells at the Threshold to 20% Efficiency. IEEE Journal of Photovoltaics, 3, 1389-1393. https://doi.org/10.1109/JPHOTOV.2013.2278661
Geisthardt, R., Topic, M. and Sites, J. (2015) Status and Potential of CdTe Solar-Cell Efficiency. IEEE Journal of Photovoltaics, 5, 1217-1221. https://doi.org/10.1109/JPHOTOV.2015.2434594
Artegiani, E., Leoncini, M., Barbato, M., Meneghini, M., Meneghesso, G., Cavallini, M. and Romeo, A. (2019) Analysis of Magnesium Zinc Oxide Layers for High Efficiency CdTe Devices. Thin Solid Films, 672, 22-25. https://doi.org/10.1016/j.tsf.2019.01.004
Song, T., Kanevce, A. and Sites, J. (2016) Emitter/Absorber Interface of CdTe Solar Cells. Journal of Applied Physics, 119, Article ID: 233104. https://doi.org/10.1063/1.4953820
Burst, J. (2016) CdTe Solar Cells with Open-Circuit Voltage Breaking the1V Barrier. Nature Energy, 1, Article No. 16015. https://doi.org/10.1038/nenergy.2016.15
Wilhelm, H., Schock, H. and Scheer, R. (2011) Interface Recombination in Heterojunction Solar Cells: Influence of Buffer Layer Thickness. Journal of Applied Physics, 109, Article ID: 084514. https://doi.org/10.1063/1.3554409
Sites, J. and Pan, J. (2006) Strategies to Increase CdTe Solar Cell Voltage. Thin Solid Films, 515, Article ID: 6099. https://doi.org/10.1016/j.tsf.2006.12.147
Munshi, A., Kephart, J., Abbas, A., Shimpi, T., Barth, K., Walls, J., et al. (2018) Polycrystalline CdTe Photovoltaics with Efficiency over 18% through Improved Absorber Passivation and Current Collection. Solar Energy Materials and Solar Cells, 176, 9-18. https://doi.org/10.1016/j.solmat.2017.11.031
Colegrove, E., Yang, J., Harvey, S., Young, M., Burst, J., Duenow, J., Albin, D., Wei, S. and Metzger, W. (2018) Experimental and Theoretical Comparison of Sb, As, and P Diffusion Mechanisms and Doping in CdTe. Journal of Physics D: Applied Physics, 51, Article ID: 075102. https://doi.org/10.1088/1361-6463/aaa67e
Kephart, J., McCamy, J., Ma, Z., Ganjoo, A., Alamgir, F. and Sampath, W. (2016) Band Alignment of Front Contact Layers for High-Efficiency CdTe Solar Cells. Solar Energy Materials and Solar Cells, 157, 266-275. https://doi.org/10.1016/j.solmat.2016.05.050
Kim, S., Suh, J., Kim, T., Hong, J. and Cho, S. (2019) Plasmon-Enhanced Performance of CdS/CdTe Solar Cells Using Au Nanoparticles. Optics Express, 27, 22017-22024. https://doi.org/10.1364/OE.27.022017
Kosyachenko, L.A., et al. (2013) Optical Absorptivity and Recombination Losses: The limitations Imposed by the Thickness of Absorber Layer in CdS/CdTe Solar Cells. Solar Energy Materials and Solar Cells, 114, 179-185. https://doi.org/10.1016/j.solmat.2013.03.003
Yang, J., Yin, W., Park, J., Ma, J. and Wei, S. (2016) Review on First-Principles Study of Defect Properties of CdTe as a Solar Cell Absorber. Semiconductor Science and Technology, 31, Article ID: 083002. https://doi.org/10.1088/0268-1242/31/8/083002
Kavanagh, S., Walsh, A. and Scanlon, D. (2021) Rapid Recombination by Cadmium Vacancies in CdTe. ACS Energy Letters, 6, 1392-1398. https://doi.org/10.1021/acsenergylett.1c00380
Li, C., et al. (2014) S-Te Interdiffusion within Grains and Grain Boundaries in CdTe Solar Cells. IEEE Journal of Photovoltaics, 4, 1636-1643. https://doi.org/10.1109/JPHOTOV.2014.2351622
Taylor, A., Major, J.D., Kartopu, G., Lamb, D., Duenow, J., Dhere, R.G., et al. (2015) A Comparative Study of Microstructural Stability and Sulphur Diffusion in CdS/CdTe Photovoltaic Devices. Solar Energy Materials and Solar Cells, 141, 341-349. https://doi.org/10.1016/j.solmat.2015.06.010
Potlog, T. (2016) Thin-Film Photovoltaic Devices Based on A2B6 Compounds. In: Tiginyanu, I., Topala, P. and Ursaki, V., Eds., Nanostructures and Thin Films for Multifunctional Applications, NanoScience and Technology, Springer, Cham, 143-186. https://doi.org/10.1007/978-3-319-30198-3_5
Kabir, M., Shahahmadi, S., Lim, V., Zaidi, S., Sopian, K. and Amin, N. (2012) Amorphous Silicon Single-Junction Thin-Film Solar Cell Exceeding 10% Efficiency by Design Optimization. International Journal of Photoenergy, 5, Article ID: 460919. https://doi.org/10.1155/2012/460919
Hossain, M.M., Ul Karim, M.M., Banik, S., Jahan, N.A. and Matin, M.A. (2016) Design of a High Efficiency Ultrathin CdTe/CdS p-i-n Solar Cell with Optimized Thickness and Doping Density of Different Layers. Proceedings of 2016 International Conference on Advances in Electrical, Electronic and Systems Engineering (ICAEES), Putrajaya, 14-16 November 2016, 305-308. https://doi.org/10.1109/ICAEES.2016.7888058
Gurumurugan, K., Mangalaraj, D., Narayandass, S. and Nakanishi, Y. (1996) DC Reactive Magnetron Sputtered CdO Thin Films. Materials Letters, 28, 307-312. https://doi.org/10.1016/0167-577X(96)00074-2
Al Qassem, A., Fedorov, V., Suman, V., Gagara, L. and Potlog, T. (2019) Improved Photovoltaic Parameters in CdTe Solar Cells by Insertion of a i-CdO Layer. Proceedings of 36th EU PVSEC 2019 Conference, Marseille, 9-13 September 2019, 673-677.
Li, J.V., Johnston, S.W., Li, X., Albin, D.S., Gessert, T.A. and Levi, D.H. (2010) Discussion of Some “Trap Signatures” Observed by Admittance Spectroscopy in CdTe Thin-Film Solar Cells. Journal of Applied Physics, 108, Article ID: 06450. https://doi.org/10.1063/1.3475373
Yun, J.H., et al. (2014) Performance Improvement in CdTe Solar Cells by Modifying the CdS/CdTe Interface with a Cd Treatment. Current Applied Physics, 14, 630-635. https://doi.org/10.1016/j.cap.2013.11.036
Li, D.B., Bista, S.S., Awni, R.A., et al. (2022) 20%-Efficient Polycrystalline Cd(Se,Te) Thin-Film Solar Cells with Compositional Gradient Near the Front Junction. Nature Communications, 13, Article No. 7849. https://doi.org/10.1038/s41467-022-35442-8
Schroder, D. (2006) Semiconductor Material and Device Characterization. 3rd Edition, Wiley, Hoboken, 63. https://doi.org/10.1002/0471749095
Castaldini, A., Cavallini, A., Fraboni, B., Fernandez, P. and Piqueras, J. (1998) Deep Energy Levels in CdTe and CdZnTe. Journal of Applied Physics, 83, Article ID: 2121. https://doi.org/10.1063/1.366946
Ochoa-Landín, R., Vigil-Galan, O., Vorobiev, Y.V. and Ramírez-Bon, R. (2009) Chemically-Deposited Te Layers Improving the Parameters of Back Contacts for CdTe Solar Cells. Solar Energy, 83, 134-138. https://doi.org/10.1016/j.solener.2008.07.005
Raadik, T., Krustok, J., Josepson, R., Hiie, J., Potlog, T. and Spalatu, N. (2013) Temperature Dependent Electroreflectance Study of CdTe Solar Cells. Thin Solid Films, 535, 279-282. https://doi.org/10.1016/j.tsf.2012.12.083
Bastola, E., Bordovalos, A., LeBlanc, E., Shrestha, N., Reese, M. and Ellingson, R. (2019) Doping of CdTe Using CuCl2 Solution for Highly Efficient Photovoltaic Devices. Proceedings of 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC), Chicago, 16-21 June 2019, 1846-1850. https://doi.org/10.1109/PVSC40753.2019.8980780
Walter, T., Herberholz, R., Müller, C. and Schock, H.W. (1996) Determination of Defect Distributions from Admittance Measurements and Application to Cu(In,Ga) Se2 Based Heterojunctions. Journal of Applied Physics, 80, 4411-4420. https://doi.org/10.1063/1.363401
Gilmore, A., Kaydanov, V., Kaydanov, V. and Ohno, T. (2000) Mobility in SnO2:F Thin Polycrystalline Films: Grain Boundary Effect and Scattering in the Grain Bulk. MRS Online Proceedings Library, 666, Article No. 310. https://doi.org/10.1557/PROC-666-F3.10
Bayhan, H. and Kavasoglu, A. (2003) Admittance and Impedance Spectroscopy on Cu(In,Ga)Se2 Solar Cells. Turkish Journal of Physics, 27, 529-535.
Gul, R., McCloy, J.S., Murugesan, M., Montag, B. and Singh, J. (2022) Cl-Doped CdTe Crystal Growth for Medical Imaging Applications. Crystals, 12, Article 1365. https://doi.org/10.3390/cryst12101365
Reislohner, U., Grillenberger, J. and Witthuhn, W. (1998) Band-Gap Level of the Cadmium Vacancy in CdTe. Journal of Crystal Growth, 184-185, 1160-1164.
Potter, M.D.G., et al. (2000) A Study of the Effects of Varying Cadmium Chloride Treatment on the Luminescent Properties of CdTe/CdS Thin Film Solar Cells. Thin Solid Films, 361-362, 248-252. https://doi.org/10.1016/S0040-6090(99)00782-8
Hoschl, P., Grill, R., Franc, J., Moravec, P. and Belas, E. (1993) Cl-Doping of Te-Rich CdTe: Complex Formation, Self-Compensation and Self-Purification from First Principle. Materials Science and Engineering B, 16, 215.
Popovych, V., Virt, I., Sizov, F., Tetyorkin, V., Tsybrii, Z., Darchuk, L., Parfenjuk, O. and Ilashchuk, M. (2007) The Effect of Chlorine Doping Concentration on the Quality of CdTe Single Crystals Grown by the Modified Physical Vapor Transport Method. Journal of Crystal Growth, 308, 63-70. https://doi.org/10.1016/j.jcrysgro.2007.07.041
Su-Huai, W. and Zhang, S. (2002) Chemical Trends of Defect Formation and Doping Limit in II-VI Semiconductors: The Case of CdTe. Physical Review B, 66, 155211. https://doi.org/10.1103/PhysRevB.66.155211
Herberholz, R., Igalson, M. and Schock, H. (1998) Distinction between Bulk and Interface States in CuInSe2/CdS/ZnO by Space Charge Spectroscopy. Journal of Applied Physics, 83, Article No. 318. https://doi.org/10.1063/1.366686
Major, J., Al Turkestani, M., Bowen, L., Brossard, M., Li, C., Lagoudakis, P. and Durose, K. (2016) A Low-Cost Non-Toxic Post-Growth Activation Step for CdTe Solar Cells. Nature Communications, 7, Article ID: 13231.
Castaldini, A., Cavallini, A., Fraboni, B., Fernandez, P. and Piqueras, J. (1996) Comparison of Electrical and Luminescence Data for the A Center in CdTe. Applied Physics Letters, 69, 3510-3512. https://doi.org/10.1063/1.117228
Kremer, R. and Leigh, W. (1988) Deep Levels in CdTe. Journal of Crystal Growth, 86, 490-496. https://doi.org/10.1016/0022-0248(90)90764-C
Maghouli, M. and Eshghi, H. (2020) Studying the Effect of Deposition Time on Physical Properties of CdTe Thin Films; Influence of CdTe Electrical Properties on CdS/CdTe Heterojunction Rectifying Behavior. Optik, 218, Article ID: 165132. https://doi.org/10.1016/j.ijleo.2020.165132
Seymour, F.H., Kaydanov, V. and Ohno, T.R. (2005) Cu and CdCl2 Influence on Defects Detected in CdTe Solar Cells with Admittance Spectroscopy. Applied Physics Letters, 87, Article ID: 153507. https://doi.org/10.1063/1.2099515
Shepidchenko, A.S., Mirbt, B., Sanyal, A., Hakansson, A. and Klintenberg, M. (2013) Small Hole Polaron in CdTe: Cd-Vacancy Revisited. Journal of Physics: Condensed Matter, 25, Article ID: 415801.
Lindstrom, A., Mirbt, S., Sanyal, B. and Klintenberg, M. (2016) High Resistivity in Undoped CdTe: Carrier Compensation of Te Antisites and Cd Vacancies. Journal of Physics D: Applied Physics, 49, Article ID: 035101. https://doi.org/10.1088/0022-3727/49/3/035101
Soundararajan, R., Lynn, S., Awadallah, C., Szeles, S. and Wei, H. (2006) Study of Defect Levels in CdTe Using Thermoelectric Effect Spectroscopy. Journal of Electronic Materials, 35, 1333-1340. https://doi.org/10.1007/s11664-006-0264-0
Becerril, M., Zelaya-Angel, O., Vargas-García, J.-R., Ramírez-Bon, R. and González-Hernández, J. (2001) Effects of Cd Vacancies on the Electrical Properties of Polycrystalline CdTe Sputtered Films. Journal of Physics and Chemistry of Solids, 62, 1081-1085. https://doi.org/10.1016/S0022-3697(00)00284-5