Band Bending at CdTe Solar Cell Contacts: Correlating Electro‐Optical and X‐Ray Photoelectron Spectroscopy Analyses of Thin Film Solar Cells

Kuciauskas, Darius; Perkins, Craig L.; Nardone, Marco; Lee, Chungho; Mallick, Rajni; Xiong, Gang

doi:10.1002/solr.202300073

Cited by 6 publications

(17 citation statements)

References 36 publications

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“…Dopants can also increase non-radiative bulk recombination (e.g., Cu in high voltage CdTe solar cells, [81,42] comparison of Cu and As doping by Onno et al, [25] and comparison of As-doped devices 4 and 5 in this study), therefore reducing bulk recombination continues to be important. Back contact recombination, interface charges, band alignments, [27] and contact selectivity [25] will likely increase in importance for absorbers with reduced electronic disorder.…”

Section: Discussionmentioning

confidence: 99%

“…Fabrication and Characterization of As-doped Solar Cells 4: The Cd-SeTe/CdTe bilayer device stack was fabricated by vapor transport deposition (VTD) with in situ As doping followed by ZnTe and metal back contact. [17,4,19,25,27] Carrier density determined with capacitance-voltage (CV) was p = 2 × 10 16 cm −3 . JV and EQE characteristics were given in Ref.…”

Section: Methodsmentioning

confidence: 99%

“…[78] When the metal back contact is a perfect reflector, V SQ OC = 1.149 V for this bandgap, [37] and device voltages are up to 902 mV. [27] The difference ( V OC − V Device 4 has V OC = 902 mV, [27] similar to V OC of the record efficiency solar cell (V OC = 899 mV). [6] Therefore, nonradiative recombination losses for device 4 are V OC − V rad OC = −(120-150) mV, comparable with radiative recombination losses introduced by the band tails.…”

Section: Voltage Losses In As-doped Solar Cellsmentioning

confidence: 97%

“…Solar cells 4 were fabricated by vapor transport deposition (VTD) and in situ As doping at First Solar. [4,19,27] Figure 5 shows PL emission data for these devices. At 4 K, As-doped devices have high radiative efficiency.…”

Section: Amplitude Of Electronic Potential Fluctuations In As-doped C...mentioning

confidence: 99%

“…[ 25 ] According to this model bulk properties (implied voltage or quasi‐Fermi level splitting) are sufficient for ≈ 1 V solar cells, but incorrect interface band offsets impede charge carrier collection. However, devices with a broad range of interface layers and interface band offsets (front–MZO, [ 20 ] SnO 2 , [ 19 ] graded Cd(O,S,Se,Te), [ 26 ] and back–TeO 2 , [ 22 ] ZnTe, [ 19,27 ] doped Al 2 O 3 [ 23 ] ) have voltages equal to or below 900 mV, making interface selectivity unlikely to dominate V OC ‐losses for such a large range of front and back contact architectures.…”

Section: Introductionmentioning

confidence: 99%

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Why Increased CdSeTe Charge Carrier Lifetimes and Radiative Efficiencies did not Result in Voltage Boost for CdTe Solar Cells

Kuciauskas

Nardone

Bothwell

et al. 2023

Advanced Energy Materials

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After a focused effort over the last decade, order‐of‐magnitude improvements in doping and electro‐optical characteristics (radiative efficiency, carrier lifetime, and passivation) have been reported for polycrystalline CdSeTe solar cells. Surprisingly, this did not result in higher solar cell voltages regardless of device contacting layers, absorber grading profiles, and other changes in device architecture. From detailed evaluation of radiative emission and carrier dynamics in CdSeTe heterostructures and devices, it is shown that the complexity introduced to the absorber to achieve lifetime and passivation metrics resulted in charge carrier trapping, which now negatively affects CdSeTe absorbers. It is found that the defects with activation energy Ea ≈ 0.14‐0.22 eV dominate radiative emission and carrier dynamics in undoped CdSeTe, and electronic potential fluctuations with the amplitude γ ≈ 45–60 meV are present in As‐doped CdSeTe/CdTe. Because of potential fluctuations, radiative voltage is reduced by ≈ −100 mV, to = 1020‐1050 mV (for 1.4 eV bandgap). For record‐efficiency solar cells with VOC ≥900 mV, radiative and nonradiative recombination voltage losses are comparable, and future research needs to focus on reducing dopant compensation which causes potential fluctuations. This represents a paradigm shift for CdTe solar cells, with non‐radiative bulk recombination no longer representing a dominant voltage loss pathway.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Voltage Losses In As-doped Solar Cellsmentioning

confidence: 97%

Section: Amplitude Of Electronic Potential Fluctuations In As-doped C...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Why Increased CdSeTe Charge Carrier Lifetimes and Radiative Efficiencies did not Result in Voltage Boost for CdTe Solar Cells

Kuciauskas

Nardone

Bothwell

et al. 2023

Advanced Energy Materials

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Understanding and Advancing Bifacial Thin Film Solar Cells under Dual Illumination

Phillips,

Friedl,

Ottinger

et al. 2023

Solar RRL

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There is a great deal of interest in increasing the energy yield from thin film solar cells by implementing bifacial operation. However, deleterious band bending and high interface recombination at the back transparent electrode can cause problems. Here, we investigate how bifacial thin film devices perform when illuminated through the front, back, and simultaneously through both interfaces using numerical modeling. We show that the downward band bending near the back interface is reduced during illumination when the carrier concentration is low. This effect is not found when the doping is relatively high, but the minority carrier distribution is still modified. Under either condition, the power generated under bifacial illumination exceeds the sum of the power generated when the illumination is solely from the back or the front. We also show that the back illuminated device performance is independent of the angle at which the light enters the back of the device, which provide accommodation for scattered light. Finally, we calculate the power enhancement for bifacial devices relative to front illuminated devices and show that any significant loss in frontside power generation is difficult to overcome with back illumination under real world albedo conditions.This article is protected by copyright. All rights reserved.

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Comprehensive Study of Carrier Recombination in High‐Efficiency CdTe Solar Cells Using Transient Photovoltage

Abudulimu,

Carter,

Phillips

et al. 2024

Solar RRL

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Cadmium telluride (CdTe) solar cells represent a commercially successful photovoltaic technology, with an annual production capacity approaching 20 GW. However, improving the open‐circuit voltage (V OC ) remains challenging. This study aims to deepen the understanding of charge carrier recombination in CdTe solar cells and to explore alternative dynamical characterization methods that address the limitations found in conventionally used time‐resolved photoluminescence (TRPL) for CdTe solar cells. We utilized transient photovoltage (TPV) and transient photocurrent (TPC) techniques to investigate charge carrier dynamics under conditions resembling real‐world solar cell operation. Our results reveal that an effective non‐radiative recombination lifetime of 580 ns dominates the charge dynamics at VOC values below 850 mV. Above this threshold, radiative recombination becomes significant, with a radiative recombination coefficient of 1.1×10‐9 cm³ s‐1. Additionally, the stationary charge carrier density at 1 sun was determined to be around 1×1014 cm‐3. By accurately determining both radiative and non‐radiative recombination, this work provides a comprehensive understanding of carrier dynamics in high‐performing CdTe devices and paves the way for improving the VOC and performance of CdTe solar cells.This article is protected by copyright. All rights reserved.

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Band Bending at CdTe Solar Cell Contacts: Correlating Electro‐Optical and X‐Ray Photoelectron Spectroscopy Analyses of Thin Film Solar Cells

Cited by 6 publications

References 36 publications

Why Increased CdSeTe Charge Carrier Lifetimes and Radiative Efficiencies did not Result in Voltage Boost for CdTe Solar Cells

Why Increased CdSeTe Charge Carrier Lifetimes and Radiative Efficiencies did not Result in Voltage Boost for CdTe Solar Cells

Understanding and Advancing Bifacial Thin Film Solar Cells under Dual Illumination

Comprehensive Study of Carrier Recombination in High‐Efficiency CdTe Solar Cells Using Transient Photovoltage

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