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Postdeposition Sulfurization of CuInSe 2 Solar Absorbers by Employing Sacrificial CuInS 2 Precursor Layers
Author(s) -
Khavari Faraz,
Saini Nishant,
Keller Jan,
Larsen Jes K.,
Sopiha Kostiantyn V.,
Martin Natalia M.,
Törndahl Tobias,
Björkman Charlotte Platzer,
Edoff Marika
Publication year - 2022
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.202100441
Subject(s) - band gap , raman spectroscopy , bilayer , solar cell , selenium , quantum efficiency , materials science , sulfur , analytical chemistry (journal) , raman scattering , chemistry , optoelectronics , optics , metallurgy , biochemistry , physics , chromatography , membrane
Herein, a new route of sulfur grading in CuInSe 2 (CISe) thin‐film solar absorbers by introducing an ultrathin (<50 nm) sacrificial sputtered CuInS 2 (CIS) layer on top of the CISe. Different CIS top layer compositions (Cu‐poor to Cu‐rich) are analyzed, before and after a high‐temperature treatment in selenium (Se)‐ or selenium+sulfur (SeS)‐rich atmospheres. An [S]/([S] + [Se]) grading from the surface into the bulk of the Se‐ and SeS‐treated samples is observed, and evidence of the formation of a mixed CuIn(S,Se) 2 phase by Raman analysis and X‐ray diffraction is provided. The optical bandgap from quantum efficiency measurements of solar cells is increased from 1.00 eV for the CISe reference to 1.14 and 1.30 eV for the Se‐ and SeS‐treated bilayer samples, respectively. A ≈150 mV higher V OC is observed for the SeS‐treated bilayer sample, but the cell exhibits blocking characteristics resulting in lower efficiency as compared with the CISe reference. This blocking is attributed to an internal electron barrier at the interface to the sulfur‐rich surface layer. The difference in reaction routes and possible ways to improve the developed sulfurization process are discussed.