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The Effect of Potassium Fluoride Postdeposition Treatments on the Optoelectronic Properties of Cu(In,Ga)Se 2 Single Crystals
Author(s) -
Ramírez Omar,
Bertrand Maud,
Debot Alice,
Siopa Daniel,
Valle Nathalie,
Schmauch Jörg,
Melchiorre Michele,
Siebentritt Susanne
Publication year - 2021
Publication title -
solar rrl
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.544
H-Index - 37
ISSN - 2367-198X
DOI - 10.1002/solr.202000727
Subject(s) - grain boundary , potassium , gallium , passivation , dopant , potassium fluoride , materials science , inorganic chemistry , fluoride , sputtering , analytical chemistry (journal) , alkali metal , chemistry , thin film , optoelectronics , doping , metallurgy , nanotechnology , microstructure , layer (electronics) , chromatography , organic chemistry
The power conversion efficiency boost of Cu(In,Ga)Se 2 in the past years has been possible due to the incorporation of heavy alkali atoms. Their addition through postdeposition treatments results in an improvement of the open‐circuit voltage, the origin of which has been associated with grain boundaries. Herein, the effect of potassium fluoride postdeposition treatments on the optoelectronic properties of a series of sodium‐free Cu(In,Ga)Se 2 single crystals with varying Cu and Ga content is discussed. Results suggest that improvement of the quasi‐Fermi level splitting can be achieved in the absence of grain boundaries, being greater in low‐gallium Cu‐poor absorbers. Secondary ion mass spectrometry reveals the presence of potassium inside the bulk of the films, suggesting that transport of potassium can occur through grain interiors. In addition, a type inversion from n to p in potassium fluoride‐treated low‐gallium Cu(In,Ga)Se 2 is observed, which along with study of the carrier lifetime demonstrates that potassium can act as a dopant. The fact that potassium on its own can alter the optoelectronic properties of Cu(In,Ga)Se 2 single crystals demonstrates that the effect of postdeposition treatments goes beyond grain boundary passivation.