Thin-Film Solar Cells with 19% Efficiency by Thermal Evaporation of CdSe and CdTe

Ablekim, Tursun; Duenow, Joel N.; Zheng, Xin; Moutinho, H. R.; Moseley, John; Perkins, Craig L.; Johnston, Steven W.; O’Keefe, Patrick; Colegrove, Eric; Albin, David S.; Reese, Matthew O.; Metzger, Wyatt K.

doi:10.1021/acsenergylett.9b02836

Cited by 115 publications

(67 citation statements)

References 30 publications

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“…This is similar to the data present by Ablekim et al where limited Se diffusion into the CdTe layer was demonstrated, with the Se content predominately in the first 500 nm. 32 Removal of the CdS layer has not however counteracted the problem of void formation due to intermixing, with numerous voids still being apparent. While the use of sputtered CdSe can clearly achieve some measure of Se diffusion through the CdTe layer during deposition, the formed CST phase may be compromised by the void formation and the lack of an effectively graded band gap.…”

Section: Resultsmentioning

confidence: 99%

Microscopic Analysis of Interdiffusion and Void Formation in CdTe_(1–x)Se_xand CdTe Layers

Baines

Bowen

Mendis

et al. 2020

ACS Appl. Mater. Interfaces

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The use of CdSe layers has recently emerged as a route to improving CdTe photovoltaics through the formation of a CdTe (1– x ) Se x (CST) phase. However, the extent of the Se diffusion and the influence it has on the CdTe grain structure has not been widely investigated. In this study, we used transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD) to investigate the impact of growing CdTe layers on three different window layer structures CdS, CdSe, and CdS/CdSe. We demonstrate that extensive intermixing occurs between CdS, CdSe, and CdTe layers resulting in large voids forming at the front interface, which will degrade device performance. The use of CdS/CdSe bilayer structures leads to the formation of a parasitic CdS (1– x ) Se x phase. Following removal of CdS from the cell structure, effective CdTe and CdSe intermixing was achieved. However, the use of sputtered CdSe had limited success in producing Se grading in CST.

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Section: Resultsmentioning

confidence: 99%

Microscopic Analysis of Interdiffusion and Void Formation in CdTe_(1–x)Se_xand CdTe Layers

Baines

Bowen

Mendis

et al. 2020

ACS Appl. Mater. Interfaces

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“…Solar cells used graded absorber, where the near-interface bandgap of %1.4 eV was due to Se alloying in CdSeTe, and in the bulk CdTe bandgap was 1.50 eV. [25] The bandgap spatial distributions in high -efficiency CdSeTe solar cells fabricated in different laboratories using semiconductor vapor transport deposition, [25,40,74] close space sublimation, [16,21] and evaporation [75] were characterized with CL on bevel and cross-sectional samples. Chemical imaging showed that heterogeneous Se and Cl distributions modulate bandgap with depth, but also within crystalline grains.…”

Section: Methodsmentioning

confidence: 99%

Identification of Recombination Losses in CdSe/CdTe Solar Cells from Spectroscopic and Microscopic Time‐Resolved Photoluminescence

2021

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Due to the lowest‐cost and best reliability, CdTe solar cells are the leading thin‐film photovoltaic technology. Increasing open‐circuit voltage by reducing recombination represents the most promising path toward further improvements. Analysis is needed to identify limitations that cause efficiency losses. To achieve this goal for Cu‐doped CdSe/CdTe solar cells, time‐resolved spectroscopy and microscopy are developed and applied. Recombination lifetimes and radiative efficiency identify that defect‐mediated recombination is the dominant voltage loss mechanism. When carrier lifetimes are averaged over many crystalline grains, they increase from 180 to 430 ns when Al2O3 is applied to the back contact. The quasi‐Fermi‐level splitting correspondingly increases from 880–905 to 906–931 mV, indicating a pathway to overcome the long‐standing 900 mV voltage limitation. However, the dominant recombination losses are attributed to the absorber bulk. From microscopic carrier lifetime measurements, it is identified that space charge fields due to charged grain boundaries (GBs) lead to recombination in the CdTe absorber bulk. At high injection, GB space charge fields are screened, but that occurs above 1 Sun excitation conditions. Alloying with selenium in the near‐interface CdSeTe absorber region reduces GB losses and is identified as one of the factors leading to high radiative and power conversion efficiency.

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“…[5][6][7][8] Meanwhile, incorporation of Se to form a ternary alloy of CdSe x Te 1Àx adjacent the emitter has further improved the current collection at longer wavelengths. [9][10][11][12][13][14][15] The Se alloy layer has been shown to be effective both because of its narrower bandgap (%1.4 eV), which allows additional photon collection, and because of the increased passivation when deployed as an absorber layer adjacent to the MZO emitter. [13,16,17] The full structure of the cells used in this work is shown in Figure 1a.…”

Section: Introductionmentioning

confidence: 99%

CdTe‐Based Solar Cells with Variations in Mg Concentration in the MgZnO Emitter

et al. 2021

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The optimal fraction of Mg incorporation in sputter‐deposited MgXZn1−XO (MZO) emitters for thin‐film CdTe‐based solar cells is evaluated by varying it over a range of x from 0 to 0.35. This range allows a variation in the conduction band offset from −0.1 eV (cliff like) to +0.32 eV (spike like). A maximum efficiency of 18.5% for cells with the bilayer CdSeTe/CdTe absorber occurs at x = 0.15, which corresponds to a spike‐like band offset near 0.2 eV, as confirmed by X‐ray photoelectron spectroscopy. In addition, good cell performance is seen over a fairly broad range of x extending from 0.1 to 0.25. The MZO optical bandgap increases with the Mg fraction, consistent with an increasing conduction band offset. Temperature‐dependent current−voltage measurements and time‐resolved photoluminescence show improvement in the emitter/absorber interface with the incorporation of Mg. Capacitance−voltage measurements show that the depletion region extends further into the absorber with more Mg, and X‐ray diffraction confirms a change from a hexagonal‐dominant crystal structure toward zinc blende at x = 0.35.

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Thin-Film Solar Cells with 19% Efficiency by Thermal Evaporation of CdSe and CdTe

Cited by 115 publications

References 30 publications

Microscopic Analysis of Interdiffusion and Void Formation in CdTe_(1–x)Se_xand CdTe Layers

Microscopic Analysis of Interdiffusion and Void Formation in CdTe_(1–x)Se_xand CdTe Layers

Identification of Recombination Losses in CdSe/CdTe Solar Cells from Spectroscopic and Microscopic Time‐Resolved Photoluminescence

CdTe‐Based Solar Cells with Variations in Mg Concentration in the MgZnO Emitter

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Thin-Film Solar Cells with 19% Efficiency by Thermal Evaporation of CdSe and CdTe

Cited by 115 publications

References 30 publications

Microscopic Analysis of Interdiffusion and Void Formation in CdTe(1–x)Sexand CdTe Layers

Microscopic Analysis of Interdiffusion and Void Formation in CdTe(1–x)Sexand CdTe Layers

Identification of Recombination Losses in CdSe/CdTe Solar Cells from Spectroscopic and Microscopic Time‐Resolved Photoluminescence

CdTe‐Based Solar Cells with Variations in Mg Concentration in the MgZnO Emitter

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Microscopic Analysis of Interdiffusion and Void Formation in CdTe_(1–x)Se_xand CdTe Layers

Microscopic Analysis of Interdiffusion and Void Formation in CdTe_(1–x)Se_xand CdTe Layers