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Title: Surface and bulk effects of K in highly efficient Cu 1-xK xInSe 2 solar cells

To advance knowledge of the beneficial effects of K in Cu(In,Ga)(Se,S) 2 (CIGS) photovoltaic (PV) absorbers, recent Cu-K-In-Se phase growth studies have been extended to PV performance. First, the effect of distributing K throughout bulk Cu 1-xK xInSe 2 absorbers at low K/(K+Cu) compositions (0 = x = 0.30) was studied. Efficiency, open-circuit voltage (VOC), and fill factor (FF) were greatly enhanced for x ~ 0.07, resulting in an officially-measured 15.0%-efficient solar cell, matching the world record CuInSe 2 efficiency. The improvements were a result of reduced interface and bulk recombination, relative to CuInSe 2 (x ~ 0). However, higher x compositions had reduced efficiency, short-circuit current density (J SC), and FF due to greatly increased interface recombination, relative to the x ~ 0 baseline. Next, the effect of confining K at the absorber/buffer interface at high K/(K+Cu) compositions (0.30 = x = 0.92) was researched. Previous work showed that these surface layer growth conditions produced CuInSe 2 with a large phase fraction of KInSe 2. After optimization (75 nm surface layer with x ~ 0.41), these KInSe 2 surface samples exhibited increased efficiency (officially 14.9%), VOC, and FF as a result of decreased interface recombination. The KInSe 2 surfacesmore » had features similar to previous reports for KF post-deposition treatments (PDTs) used in world record CIGS solar cells - taken as indirect evidence that KInSe 2 can form during these PDTs. Both the bulk and surface growth processes greatly reduced interface recombination. However, the KInSe 2 surface had higher K levels near the surface, greater lifetimes, and increased inversion near the buffer interface, relative to the champion bulk Cu 1-xK xInSe 2 absorber. These characteristics demonstrate that K may benefit PV performance by different mechanisms at the surface and in the absorber bulk.« less
ORCiD logo [1] ;  [2] ;  [3] ;  [3] ;  [4]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States); Univ. of Florida, Gainesville, FL (United States)
  2. National Cheng Kung Univ., Tainan City (Taiwan)
  3. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  4. Univ. of Florida, Gainesville, FL (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 0927-0248
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Solar Energy Materials and Solar Cells
Additional Journal Information:
Journal Volume: 185; Journal Issue: C; Journal ID: ISSN 0927-0248
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)
Country of Publication:
United States
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; Cu(In,Ga)Se2; CIGS; chalcopyrite; potassium; efficient; alloy
OSTI Identifier: