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1. Characterization of thin CdTe solar cells with a CdSeTe front layer

   https://doi.org/10.1557/adv.2019.332  

   Bothwell, Alexandra M.; Drayton, Jennifer A.; Jundt, Pascal M.; Sites, James R. (January 2019, MRS Advances)

   ABSTRACT Thin CdTe photovoltaic device efficiencies show significant improvement with the incorporation of a CdSeTe alloy layer deposited between a MgZnO emitter and CdTe absorber. CdTe and CdSeTe/CdTe devices fabricated by close-space sublimation with a total absorber thickness of 1.5 µm are studied using microscopy measurements and show minimal diffusion of Se into the CdTe. Current loss analysis shows that the CdSeTe layer is the primary absorber in the CdSeTe/CdTe structure, and fill factor loss analysis shows that ideality-factor reduction is the dominant mechanism of fill factor loss. Improvement in the CdSeTe/CdTe absorber quality compared to CdTe is also reflected in spectral and time-resolved photoluminescence measurements. Current density vs. voltage measurements show an increase in current density of up to 2 mA/cm 2 with the addition of CdSeTe due to a band gap shift from 1.5 to 1.42 eV for CdTe and CdSeTe/CdTe absorbers respectively. Voltage deficit is lower with the incorporation of the CdSeTe layer, corroborated by improved electroluminescence intensity. The addition of CdSeTe into CdTe device structures has increased device efficiencies from 14.7% to 15.6% for absorbers with a total thickness less than two microns. 

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2. Doping CdSe _x Te _1-x /CdTe Graded Absorber Films with Arsenic for Thin-Film Photovoltaics

   https://doi.org/10.1109/PVSC40753.2019.8981239  

   Munshi, Amit H.; Guo, Jinglong; Klie, Robert; Sampath, Walajabad S.; Danielson, Adam H.; Swain, Santosh; Reich, Carey L.; Shimpi, Tushar M.; McPherson, Seth W.; Lynn, Kelvin G.; et al (June 2019, 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC))

   CdTe thin-film photovoltaics have demonstrated some of the lowest costs of electricity generation owing to its low material cost and ease of manufacturing. However, the full potential of polycrystalline CdTe photovoltaics can only be realized if the open-circuit voltage can be increased beyond 1 V Open-circuit voltage ~850-900 mV has been consistently observed for state-of-the-art polycrystalline CdTe solar cells. Open-circuit voltage of over 1V has been demonstrated for single crystal CdTe devices by doping with Group V elements. Therefore, this study is aimed at understanding behavior of polycrystalline CdTe devices with arsenic doping, its activation and process and performance optimization in order to overcome current voltage limitations in CdTe solar cells. 

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3. Photovoltaic Characteristics of PERC-Like CdTe Solar Cells

   Roy, E.; Powell, K.; Yoon, H. (June 2023, Electronic Materials Conference)

   Rapid progress has been achieved in thin film CdTe solar cells, reaching a power conversion efficiency of 22.1 %. Researchers demonstrated a short-circuit current density (Jsc) of ≈ 31 mA/cm2 and a fill factor (FF) of ≈ 79 %, close to the theoretically calculated maximum values. However, the open-circuit voltage (Voc) remains below 0.9 V, much lower than the estimated Voc of 1.2 V. One strategy to improve the Voc is to implement a passivated back-contact on CdTe that can reduce the recombination by repelling minority carriers at the surface (i.e., electrons in CdTe). An aluminum oxide thin film (Al2O3) is an attractive candidate owing to its innate fixed negative charges (1012 ~ 1013 cm-2). Here, we use a patterned Al2O3 layer on CdTe to produce PERC-like CdTe solar cells (CdTe PERC). 

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4. Local Photovoltaic Measurements of CdTe Solar Cells Using Microscale Point Back-Contacts

   Powell, Kaden; Hsu, Yulin; Magginetti, David; Yoon, Heayoung (June 2021, electronic materials conference)

   Cadmium telluride (CdTe) thin-film semiconductors exhibit many desirable properties for low-cost and high-efficiency photovoltaic (PV) technology, including inherent robustness of inorganic absorber, a direct bandgap that allows full absorption of the solar spectrum with thicknesses of only few microns, and inexpensive and high-throughput manufacturing processes. At the best efficiency of 22 %, the power conversion efficiency of CdTe PVs is still well below the maximum theoretical limit (approximately 30 %). It has been suggested that the inferior efficiency is mainly attributed to the inherent polycrystalline nature of CdTe absorber (e.g., grains, grain boundaries). Understanding local photocarrier dynamics is vital to overcoming roadblocks toward higher efficiency CdTe PVs. However, conventional cell-level PV measurements often limit the microstructural analysis. In this work, we present a local PV characterization technique using point back-contacts. The thin-film CdTe solar cells used in this work were prepared by CSS (close-spaced sublimation) on a stack of n-type window layer (e.g., CdS) / transparent conductive layer (TCO; e.g., SnO2) / glass substrate. 

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5. Cadmium Telluride Cells on Silicon as Precursors for Two-Junction Tandem Cells

   Pandey, R.; Drayton, J.; Gregory, C.; Mohan Kumar, N.; Tyler, K.; King, R.; Sites, J. (January 2020, Conference record of the IEEE Photovoltaic Specialists Conference)

   Cadmium telluride and silicon are among the widely used absorber materials in photovoltaic industry. A tandem solar cell of these two can absorb significant portion of solar spectrum to yield high efficiency due to the added voltage of the two solar cells. On basis of low-cost production, a CdTe/Si cell has the potential to produce low-cost and high efficiency tandem PV. The CdTe top cell in a substrate configuration is essential to achieve a tandem between CdTe and Si. A functional CdS/CdTe solar cell in the substrate configuration was fabricated on a Si wafer. Current -Voltage measurements show a diode-like curve with lower J-V parameters compared to standard CdS/CdTe cells. SCAPS simulations were performed to identify possible reasons for poor performance and help improve the device performance. 

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