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Alkali Atoms Diffusion Mechanism in CuInSe 2 Explained by Kinetic Monte Carlo Simulations
Author(s) -
Kormath Madam Raghupathy Ramya,
Kühne Thomas D.,
Henkelman Graeme,
Mirhosseini Hossein
Publication year - 2019
Publication title -
advanced theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.068
H-Index - 17
ISSN - 2513-0390
DOI - 10.1002/adts.201900036
Subject(s) - alkali metal , diffusion , kinetic energy , ion , kinetic monte carlo , chemistry , atomic diffusion , lattice (music) , lattice diffusion coefficient , interstitial defect , crystallographic defect , chemical physics , monte carlo method , materials science , crystallography , effective diffusion coefficient , thermodynamics , physics , doping , statistics , mathematics , quantum mechanics , medicine , optoelectronics , organic chemistry , radiology , acoustics , magnetic resonance imaging
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.