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Title: The effect of Na on Cu-K-In-Se thin film growth

Journal Article · · Journal of Crystal Growth
 [1];  [2];  [3]
  1. Univ. of Florida, Gainesville, FL (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Univ. of Florida, Gainesville, FL (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Univ. of Florida, Gainesville, FL (United States)
+ Show Author Affiliations

Co-evaporation of Cu-KF-In-Se was performed on substrates with varied Na supply. Compositions of interest for photovoltaic absorbers were studied, with ratios of (K + Cu)/In ~ 0.85 and K/(K + Cu) ~ 0-0.57. Bare soda-lime glass (SLG) substrates had the highest Na supply as measured by secondary ion mass spectrometry, while SLG/Mo and SLG/SiO2/Mo substrates led to 3x and 3000x less Na in the growing film, respectively. Increased Na supply favored Cu1-xKxInSe2 (CKIS) alloy formation as proven by X-ray diffraction (XRD), while decreased Na supply favored the formation of CuInSe2 + KInSe2 mixed-phase films. Scanning electron microscopy and energy dispersive X-ray spectroscopy revealed the KInSe2 precipitates to be readily recognizable planar crystals. Extrinsic KF addition during film growth promoted diffusion of Na out from the various substrates and into the growing film, in agreement with previous reports. Time-resolved photoluminescence showed enhanced minority carrier lifetimes for films with moderate K compositions (0.04 < K/(K + Cu) < 0.14) grown on SLG/Mo. Due to the relatively high detection limit of KInSe2 by XRD and the low magnitude of chalcopyrite lattice shift for CKIS alloys with these compositions, it is unclear if the lifetime gains were associated with CKIS alloying, minor KInSe2 content, or both. The identified Na-K interdependency can be used to engineer alkali metal bonding in Cu(In,Ga)(Se,S)2 absorbers to optimize both initial and long-term photovoltaic power generation.

Research Organization:
National Renewable Energy Laboratory (NREL), Golden, CO (United States)
Sponsoring Organization:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
Grant/Contract Number:
AC36-08GO28308
OSTI ID:
1427350
Report Number(s):
NREL/JA--5K00-71039
Journal Information:
Journal of Crystal Growth, Journal Name: Journal of Crystal Growth Journal Issue: C Vol. 488; ISSN 0022-0248
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (1)

Revealing the beneficial role of K in grain interiors, grain boundaries, and at the buffer interface for highly efficient CuInSe 2 solar cells
  • Muzzillo, Christopher P.; Poplawsky, Jonathan D.; Tong, Ho Ming
  • Progress in Photovoltaics: Research and Applications, Vol. 26, Issue 10 https://doi.org/10.1002/pip.3022
journal June 2018

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