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Comparison of Sulfur Incorporation into CuInSe 2 and CuGaSe 2 Thin‐Film Solar Absorbers
Author(s) -
Khavari Faraz,
Keller Jan,
Larsen Jes K.,
Sopiha Kostiantyn V.,
Törndahl Tobias,
Edoff Marika
Publication year - 2020
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.202000415
Subject(s) - annealing (glass) , sulfur , selenium , solar cell , chemistry , analytical chemistry (journal) , alloy , diffusion , materials science , crystallography , chemical engineering , metallurgy , optoelectronics , thermodynamics , physics , chromatography , engineering
Herein, sulfurization of CuInSe 2 and CuGaSe 2 (CGSe) absorber layers is compared to improve the understanding of sulfur incorporation into Cu(In,Ga)Se 2 films by annealing in a sulfur atmosphere. It is found for Cu‐poor CuInSe 2 that for an annealing temperature of 430 °C, sulfur is incorporated into the surface of the absorber and forms an inhomogeneous CuIn(S,Se) 2 layer. In addition, at 530 °C, a surface layer of CuInS 2 is formed. In contrast, for Cu‐poor CuGaSe 2 samples, S can only be introduced at 530 °C, mainly forming an alloy of CuGa(S,Se) 2 , where no closed CuGaS 2 layer is found. In Cu‐rich CuGaSe 2 samples, however, selenium is substituted by S already at 330 °C, which can be explained by a rapid phase transformation of Cu 2 − x Se into Cu 2 − x (S,Se). This transformation facilitates S in‐diffusion and catalyzes CuGa(S,Se) 2 formation, likewise that previously reported to occur in CuInSe 2 . Finally, the Cu‐poor CuInSe 2 solar cell performance is improved by the sulfurization step at 430 °C, whereas for the 530 °C sample, a decreasing fill factor and short‐circuit current density are observed, indicating lower diffusion length accompanied by possible formation of an electron transport barrier. In contrast, the electrical characteristics deteriorate for all sulfurized Cu‐poor CuGaSe 2 cells.