Na‐Diffusion Enhanced p‐type Conductivity in Cu(In,Ga)Se<sub>2</sub>: A New Mechanism for Efficient Doping in Semiconductors

Yuan, Zhen-Kun; Chen, Shiyou; Xie, Yanwu; Park, Ji-Sang; Xiang, Hongjun; Gong, X. G.; Wei, Su‐Huai

doi:10.1002/aenm.201601191

Cited by 131 publications

(126 citation statements)

References 68 publications

(187 reference statements)

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“…The vacancymediated diffusion of Na has a larger migration barrier than those of K and Rb, whereas interstitial Na (Na i ) atoms diffuse faster than heavier AM in the interstitial site. It was suggested by Yuan et al [44] that the outdiffusion of Na and K atoms from the absorber layer could be the reason for the enhancement of hole concentration. [39] In addition, the presence of Na atoms in the grain interior (GI) indicates the high mobility of Na atoms (Na interstitial diffusion).…”

Section: Introductionmentioning

confidence: 99%

Alkali Atoms Diffusion Mechanism in CuInSe₂ Explained by Kinetic Monte Carlo Simulations

Raghupathy

Kühne

Henkelman

et al. 2019

Advcd Theory and Sims

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Adaptive kinetic Monte Carlo simulation (aKMC) is employed to study the dynamics and the diffusion of point defects in the CuInSe 2 lattice. The aKMC results show that lighter alkali atoms can diffuse into the CuInSe 2 grains, whereas the diffusion of heavier alkali atoms is limited to the Cu-poor region of the absorber. The key difference between the diffusion of lighter and heavier alkali elements is the energy barrier of the ion exchange between alkali interstitial atoms and Cu. For lighter alkali atoms like Na, the interstitial diffusion and the ion-exchange mechanism have comparable energy barriers. Therefore, Na interstitial atoms can diffuse into the grains and replace Cu atoms in the CuInSe 2 lattice. In contrast to Na, the ion-exchange mechanism occurs spontaneously for heavier alkali atoms like Rb and the further diffusion of these atoms depends on the availability of Cu vacancies. The outdiffusion of alkali substitutional atoms from the grains results in the formation of Cu vacancies which in turn increases the hole concentration in the absorber. In this respect, Na is more efficient than Rb due to the higher concentration of Na substitutional defects in the CuInSe 2 grains.

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Section: Introductionmentioning

confidence: 99%

Alkali Atoms Diffusion Mechanism in CuInSe₂ Explained by Kinetic Monte Carlo Simulations

Raghupathy

Kühne

Henkelman

et al. 2019

Advcd Theory and Sims

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“…From computational studies 29,30 , the capture of Na by V Cu and formation of sodium on copper (Na Cu ) antisite defects in CIGS seems thermodynamically favourable, even considering the most recent Na Cu formation energies calculated with a more reasonable Na electrochemical potential 31,32 . However, it is well known that Na segregates mostly to grain boundaries 33–35 .…”

Section: Introductionmentioning

confidence: 99%

Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers

et al. 2018

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Copper indium gallium diselenide-based technology provides the most efficient solar energy conversion among all thin-film photovoltaic devices. This is possible due to engineered gallium depth gradients and alkali extrinsic doping. Sodium is well known to impede interdiffusion of indium and gallium in polycrystalline Cu(In,Ga)Se2 films, thus influencing the gallium depth distribution. Here, however, sodium is shown to have the opposite effect in monocrystalline gallium-free CuInSe2 grown on GaAs substrates. Gallium in-diffusion from the substrates is enhanced when sodium is incorporated into the film, leading to Cu(In,Ga)Se2 and Cu(In,Ga)3Se5 phase formation. These results show that sodium does not decrease per se indium and gallium interdiffusion. Instead, it is suggested that sodium promotes indium and gallium intragrain diffusion, while it hinders intergrain diffusion by segregating at grain boundaries. The deeper understanding of dopant-mediated atomic diffusion mechanisms should lead to more effective chemical and electrical passivation strategies, and more efficient solar cells.

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“…[12][13][14][15][16][17] The most common approach for the incorporation of alkali atoms in CIGS layer was their natural diffusion from SLG substrate which contained Na and sometimes also K. 18,19 The incorporation of alkali atoms could greatly enhance both the structural and the electrical properties of CIGS absorber materials in comparison with the sodium-free glass. [12][13][14][15][16][17] The most common approach for the incorporation of alkali atoms in CIGS layer was their natural diffusion from SLG substrate which contained Na and sometimes also K. 18,19 The incorporation of alkali atoms could greatly enhance both the structural and the electrical properties of CIGS absorber materials in comparison with the sodium-free glass.…”

Section: Introductionmentioning

confidence: 99%

“…19,21,22 However, excessive Na diffusion from the SLG substrate not only hindered the grain size of CIGS film but also degraded its electrical property as well as the device performances with higher defect density. 16 Very recently, some researchers have conducted an oxidation treatment to their Mo back contact films prior to CIGS deposition and believed that MoO 3 on the surface of Mo back contact plays a key role by reacting with alkali cations from glass and releasing them towards CIGS film upon an alkali concentration difference. 16 Very recently, some researchers have conducted an oxidation treatment to their Mo back contact films prior to CIGS deposition and believed that MoO 3 on the surface of Mo back contact plays a key role by reacting with alkali cations from glass and releasing them towards CIGS film upon an alkali concentration difference.…”

Section: Introductionmentioning

confidence: 99%

Role of surface microstructure of Mo back contact on alkali atom diffusion and Ga grading in Cu(In,Ga)Se₂ thin film solar cells

Gong

Kong

et al. 2019

Energy Science & Engineering

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While the major function of molybdenum (Mo) back contact on soda‐lime glass (SLG) substrate in Cu(In,Ga)Se2 (CIGS) solar cells is to provide good adhesion and good conductivity, its role as the transportation channel for alkali elements from SLG substrate to CIGS layer has often been overlooked. In this work, we have intentionally fabricated tri‐layered structure in contrast to the conventional bi‐layered structure for Mo back contact with the microstructure of the thin topmost Mo layer manipulated by the Ar pressure and water vapor during sputtering deposition. It has been discovered that the CIGS solar cell conversion efficiency can be greatly affected by this thin topmost Mo layer of the back contact. Investigations on the elemental depth profiles in the CIGS devices and the chemical states of Mo on the back contact surfaces have revealed that the surface layer of Mo back contact has a strong effect on the diffusion of alkali elements from SLG into CIGS absorber layer, which in turn influences the formation of Ga gradient in the CIGS layer and thus the solar cell performance. It was revealed that Mo(OH)6 and MoO3 formed on the surface of Mo back contact play a key role in determining the K atom distribution and Ga gradient. A reaction mechanism was also proposed.

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Na‐Diffusion Enhanced p‐type Conductivity in Cu(In,Ga)Se₂: A New Mechanism for Efficient Doping in Semiconductors

Cited by 131 publications

References 68 publications

Alkali Atoms Diffusion Mechanism in CuInSe₂ Explained by Kinetic Monte Carlo Simulations

Alkali Atoms Diffusion Mechanism in CuInSe₂ Explained by Kinetic Monte Carlo Simulations

Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers

Role of surface microstructure of Mo back contact on alkali atom diffusion and Ga grading in Cu(In,Ga)Se₂ thin film solar cells

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Na‐Diffusion Enhanced p‐type Conductivity in Cu(In,Ga)Se2: A New Mechanism for Efficient Doping in Semiconductors

Cited by 131 publications

References 68 publications

Alkali Atoms Diffusion Mechanism in CuInSe2 Explained by Kinetic Monte Carlo Simulations

Alkali Atoms Diffusion Mechanism in CuInSe2 Explained by Kinetic Monte Carlo Simulations

Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers

Role of surface microstructure of Mo back contact on alkali atom diffusion and Ga grading in Cu(In,Ga)Se2 thin film solar cells

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Na‐Diffusion Enhanced p‐type Conductivity in Cu(In,Ga)Se₂: A New Mechanism for Efficient Doping in Semiconductors

Alkali Atoms Diffusion Mechanism in CuInSe₂ Explained by Kinetic Monte Carlo Simulations

Alkali Atoms Diffusion Mechanism in CuInSe₂ Explained by Kinetic Monte Carlo Simulations

Role of surface microstructure of Mo back contact on alkali atom diffusion and Ga grading in Cu(In,Ga)Se₂ thin film solar cells