Chemistry of K in Cu(In,Ga)Se2 photovoltaic absorbers: Effects of temperature on Cu-K-In-Se films

JOURNAL OF ALLOYS AND COMPOUNDS

卷:726

Article

Muzzillo, Christopher P.^1,2  Tong, Ho Ming^2,3  Anderson, Tim² 

[1] Natl Renewable Energy Lab, Golden, CO 80401 USA

[2] Univ Florida, Dept Chem Engn, Gainesville, FL 32611 USA

[3] Oak Ridge Natl Lab, Oak Ridge, TN 37831 USA

关键词: Photovoltaics;    Solar cells;    Semiconductors;    Phase transformation;    Thin films;    Physical vapor deposition;   

DOI  :  10.1016/j.jallcom.2017.08.019

来源: Elsevier

【 摘 要 】

Incorporation of K has led to world record Cu(In,Ga)Se-2 photovoltaic power conversion efficiencies, but there is poor consensus about the role of phase impurities in these advances. This work lays a foundation for identifying and controlling these phase impurities. Films of Cu-K-In-Se were co-evaporated at varied K/(K + Cu) compositions and substrate temperatures (with constant (K + Cu)/In similar to 0.85). Increased Na composition on the substrate's surface and decreased growth temperature were both found to favor Cu1-xKxInSe2 alloy formation, relative to two-phase CuInSe2+KInSe2 formation. Structures from X-ray diffraction (XRD), band gaps, resistivities, minority carrier lifetimes and carrier concentrations from time-resolved photoluminescence were in agreement with previous reports, where low K/(K + Cu) composition films exhibited properties promising for photovoltaic absorbers. Films grown at 400-500 degrees C were then annealed to 600 degrees C in a controlled Se ambient, which caused K loss by evaporation in proportion to the initial K/(K + Cu) composition. Similar to growth emperature, annealing drove Cu1-xKxInSe2 alloy consumption and CuInSe2+KInSe2 production, as evidenced by high temperature XRD. Annealing also decomposed KInSe2 and formed K(2)ln(12)Se(19). At high temperature, the KInSe2 crystal lattice gradually contracted as temperature and time increased, as well as just time. Evaporative loss of K during annealing could accompany the generation of vacancies on K lattice sites, and may explain the KInSe2 lattice contraction. This knowledge of Cu-K-In-Se material chemistry may be used to predict and control minor phase impurities in Cu(In,Ga)(Se,S)(2) photovoltaic absorbers-where impurities below typical detection limits may have played a role in recent world record photovoltaic efficiencies that utilized KF post-deposition treatments. Published by Elsevier B.V.

【 授权许可】

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