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Title: Properties of Cu 1–xK xInSe 2 alloys

Adding potassium to Cu(In,Ga)Se 2 absorbers has been shown to enhance photovoltaic power conversion efficiency. To illuminate possible mechanisms for this enhancement and limits to beneficial K incorporation, the properties of Cu 1-xK xInSe 2 (CKIS) thin-film alloys have been studied. Films with K/(K + Cu), or x, from 0 to 1 were grown by co-evaporation, and probed by XRF, EPMA, SEM, XRD, UV-Visible spectroscopy, current-voltage, and TRPL measurements. Composition from in situ quartz crystal and EIES monitoring was well correlated with final film composition. Crystal lattice parameters showed linear dependence on x, indicating complete K incorporation and coherent structural character at all compositions in the <100> and <010> lattice directions, despite the different symmetries of CuInSe 2 and KInSe 2. The band gap energy showed pronounced bowing with x composition, in excellent agreement with experimental reports and semiconductor theory. Films of Mo/CKIS/Ni were non-ohmic, and increasing x from 0 to 0.58 decreased the apparent CKIS resistivity. Further evidence of decreased CKIS resistivity was observed with photoluminescence response, which increased by about half a decade for x > 0, and indicates increased majority carrier concentration. Minority carrier lifetimes increased by about an order of magnitude for films grown at xmore » = 0.07 and 0.14, relative to CuInSe 2 and x ≥ 0.30. As a result, this is the first report of a Cu-K-In-Se film with >1 at.% K, and the observed property changes at increased x (wider band gap; lower resistivity; increased lifetime) comprise valuable photovoltaic performance-enhancement strategies, suggesting that CKIS alloys have a role to play in future engineering advances.« less
Authors:
 [1] ;  [2] ;  [2] ;  [3]
  1. Univ. of Florida, Gainesville, FL (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States). National Center for Photovoltaics
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  3. Univ. of Florida, Gainesville, FL (United States)
Publication Date:
Report Number(s):
NREL/JA-5K00-67323
Journal ID: ISSN 0022-2461
Grant/Contract Number:
AC36-08GO28308; FOA-0000492
Type:
Accepted Manuscript
Journal Name:
Journal of Materials Science
Additional Journal Information:
Journal Volume: 51; Journal Issue: 14; Journal ID: ISSN 0022-2461
Publisher:
Springer
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S); SunShot Foundational Program to Advance Cell Efficiency (F-PACE)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; photovoltaic power conversion; thin films; composition; Cu(In,Ga)Se2; CIGS; chalcopyrite; (Cu,K)InSe2; potassium; alloy
OSTI Identifier:
1329988