Degradation Mechanism in Cu(In,Ga)Se<sub>2</sub> Material and Solar Cells Due to Moisture and Heat Treatment of the Absorber Layer

Karki, Shankar; Paul, Pran K.; Deitz, Julia I.; Poudel, Deewakar; Rajan, Grace; Belfore, Benjamin; Danilov, Evgeny O.; Castellano, Felix N.; Grassman, Tyler J.; Arehart, Aaron R.; Rockett, Angus; Marsillac, Sylvain

doi:10.1109/jphotov.2019.2912707

Cited by 17 publications

(9 citation statements)

References 22 publications

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“… The improved N cv could contribute to V oc gain. After calculation using the method, the V oc gain from N cv improvement is 26.6 mV for the cell with a 80 nm RT-CIGS layer, while the total V oc gain is about 80 mV from I–V measurement. − …”

Section: Resultsmentioning

confidence: 99%

Above 15% Efficient Directly Sputtered CIGS Solar Cells Enabled by a Modified Back-Contact Interface

Dai

Gao

et al. 2021

ACS Appl. Mater. Interfaces

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The Schottky back-contact barrier at the Mo/Cu(In,Ga)Se2 (CIGS) interface is one of the critical issues that restrict the photovoltaic performance of CIGS solar cells. The formation of a MoSe2 intermediate layer can effectively reduce this back-contact barrier leading to efficient hole transport. However, the selenium-free atmosphere is unfavorable for the formation of the desired MoSe2 intermediate layer if the CIGS films are prepared by the commonly used direct sputtering process. In this work, high-efficiency CIGS solar cells with a MoSe2 intermediate layer were fabricated by the direct sputtering process without a selenium atmosphere. This is enabled by an intermediate CIGS layer deposited on the Mo substrate at room temperature before being ramped to a high temperature (600 °C). The room-temperature-deposited amorphous CIGS intermediate layer is Se rich, which reacts with the Mo substrate and forms very thin MoSe2 at the interface during the high-temperature process. The formed MoSe2 decreased the CIGS/Mo barrier height for better hole transport. Consequently, the CIGS solar cell with an 80 nm intermediate layer achieved a power conversion efficiency of up to 15.8%, which is a benchmark efficiency for the direct sputtering process without Se supply. This work provides the industry a new approach for commercialization of directly sputtered CIGS solar cells.

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Section: Resultsmentioning

confidence: 99%

Above 15% Efficient Directly Sputtered CIGS Solar Cells Enabled by a Modified Back-Contact Interface

Dai

Gao

et al. 2021

ACS Appl. Mater. Interfaces

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“…The mechanisms of the degradation of SLG/Mo and SLG/Mo/ CIGS interface taking into account the formation of confined zone and the interplay between the layers are schematically summed up in Sodium (and potassium) migration during aging through the solar cell was already described in the literature. 15,20,26,70 Sodium is reported beneficial for cell performance 71 but detrimental for long-term stability, decreasing the fill factor and open circuit potential. 20,26,70 Sodium accumulates at the CIGS grain boundaries, forming shunt paths that degrade electrical properties of the cell.…”

Section: Cigs Chemical Evolution Near Mo/cigs Interfacementioning

confidence: 99%

“…15,20,26,70 Sodium is reported beneficial for cell performance 71 but detrimental for long-term stability, decreasing the fill factor and open circuit potential. 20,26,70 Sodium accumulates at the CIGS grain boundaries, forming shunt paths that degrade electrical properties of the cell. 8 Diffusion of anions such as molybdates through the CIGS layer is expected to increase Na + migration thus contributing to the accelerated degradation.…”

Section: Cigs Chemical Evolution Near Mo/cigs Interfacementioning

confidence: 99%

“…[22][23][24][25] Alkali elements (Na, K) are observed to be redistributed after aging. 20,26 The removal of corrosion products by mechanical scribing or chemical etching (e.g., using KCN) allowed the cell to recover its initial performance. 22,23 Since CIGS layer growth might be influenced by molybdenum morphology and composition, it can be expected that the Mo/CIGS interface is relevant in the long-term stability of PV cells.…”

Section: Introductionmentioning

confidence: 99%

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Synergistic effect between molybdenum back contact and CIGS absorber in the degradation of solar cells

Debono,

L'Hostis,

Rebai

et al. 2023

Progress in Photovoltaics

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The stability of molybdenum (Mo) back contact and Cu (InxGa(1‐x)Se2(CIGS) absorber layers interfaces relevant for CIGS‐based solar cells was investigated using accelerated aging test, considering humidity and temperature daily variations as well as atmospheric pollution. Different configurations of sputtered Mo and co‐evaporated CIGS layers deposited on soda lime glass with or without ALD‐Al2O3 encapsulation were investigated. They were exposed for 14 days to 24 h‐cycles of temperature and humidity (25°C at 85% RH and 80°C at 30% RH) with and without solution of the pollutant salts (NaCl, Na2SO4, and (NH4)2SO4) deposited as drops on the sample to mimic marine, industrial, and rural atmospheric conditions, respectively. ALD‐Al2O3 encapsulation failed to protect the samples against the pollutants regardless of configuration. The evolution of the films was characterized by Raman spectroscopy, grazing incidence X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy. Unencapsulated Mo degraded forming a mixture of oxides (MoO2, MoO3, and Mo8O23). Unencapsulated CIGS on glass substrates was not altered, whereas dark spots were visible at the surface of Mo/CIGS configurations. Further characterization evidenced that even though the Mo layer was buried, its corrosion products were formed on top of CIGS. Mo corrosion products and copper selenide, Cu2‐xSe, were identified in dark spots. Their formation and evolution were further investigated by in situ Raman spectroscopy. A speculative mechanism explaining the interplay of molybdenum and CIGS layers during aging is proposed. In place of Mo oxides, detected on the open surface of bare Mo, soluble molybdates are expected in confined environment where alkalinity locally increases. The molybdate ions may then react with sodium ions accumulated at the grain boundaries of CIGS, forming Na2MoO4. The latter could form Na2Mo2O7 during drying because of pH decrease by atmospheric CO2 adsorption. High pH in confined zone, combined with relatively high temperature, is also believed to lixiviate gallium into soluble tetragallates [Ga (OH)4]2−, which could precipitate into Ga2O3 with pH decrease leaving Ga depleted Cu2‐xSe.

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“…Furthermore, the study of water-induced degradation, comparable to corrosion, is rarely studied. In previous publications, we have analyzed the impact of water on both CIGS and molybdenum components of CIGS devices [6,7]. However, the front transparent conductive oxide (TCO) layers are also of paramount importance.…”

Section: Introductionmentioning

confidence: 99%

Degradation Mechanism Due to Water Ingress Effect on the Top Contact of Cu(In,Ga)Se2 Solar Cells

et al. 2020

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The impact of moisture ingress on the surface of copper indium gallium diselenide (CIGS) solar cells was studied. While industry-scale modules are encapsulated in specialized polymers and glass, over time, the glass can break and the encapsulant can degrade. During such conditions, water can potentially degrade the interior layers and decrease performance. The first layer the water will come in contact with is the transparent conductive oxide (TCO) layer. To simulate the impact of this moisture ingress, complete devices were immersed in deionized water. To identify the potential sources of degradation, a common window layer for CIGS devices—a bilayer of intrinsic zinc oxide (i-ZnO) and conductive indium tin oxide (ITO)—was deposited. The thin films were then analyzed both pre and post water soaking. To determine the extent of ingress, dynamic secondary ion mass spectroscopy (SIMS) was performed on completed devices to analyze impurity diffusion (predominantly sodium and potassium) in the devices. The results were compared to device measurements, and indicated a degradation of device efficiency (mostly fill factor, contrary to previous studies), potentially due to a modification of the alkali profile.

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Degradation Mechanism in Cu(In,Ga)Se₂ Material and Solar Cells Due to Moisture and Heat Treatment of the Absorber Layer

Cited by 17 publications

References 22 publications

Above 15% Efficient Directly Sputtered CIGS Solar Cells Enabled by a Modified Back-Contact Interface

Above 15% Efficient Directly Sputtered CIGS Solar Cells Enabled by a Modified Back-Contact Interface

Synergistic effect between molybdenum back contact and CIGS absorber in the degradation of solar cells

Degradation Mechanism Due to Water Ingress Effect on the Top Contact of Cu(In,Ga)Se2 Solar Cells

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Degradation Mechanism in Cu(In,Ga)Se2 Material and Solar Cells Due to Moisture and Heat Treatment of the Absorber Layer

Cited by 17 publications

References 22 publications

Above 15% Efficient Directly Sputtered CIGS Solar Cells Enabled by a Modified Back-Contact Interface

Above 15% Efficient Directly Sputtered CIGS Solar Cells Enabled by a Modified Back-Contact Interface

Synergistic effect between molybdenum back contact and CIGS absorber in the degradation of solar cells

Degradation Mechanism Due to Water Ingress Effect on the Top Contact of Cu(In,Ga)Se2 Solar Cells

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Degradation Mechanism in Cu(In,Ga)Se₂ Material and Solar Cells Due to Moisture and Heat Treatment of the Absorber Layer