Surface and Bulk Effects of K in Cu1-xKxIn1-yGaySe2 Solar Cells

Christopher Muzzillo, Timothy Anderson

Research output: Contribution to journalArticlepeer-review

11 Scopus Citations


Two strategies for enhancing photovoltaic (PV) performance in chalcopyrite solar cells were investigated: Cu1−xKxIn1−yGaySe2 absorbers with low K content (K/(K+Cu), or x ~ 0.07) distributed throughout the bulk, and CuIn1−yGaySe2 absorbers with KIn1−yGaySe2 grown on their surfaces. Distributing K throughout the bulk absorbers improved power conversion efficiency, open-circuit voltage (VOC) and fill factor (FF) for Ga/(Ga+In) of 0, 0.3 and 0.5. Surface KIn1−yGaySe2 and bulk x ~ 0.07 Cu1−xKxIn1−yGaySe2 films with Ga/(Ga+In), or y of 0.3 and 0.5 also had improved efficiency, VOC, and FF, relative to CuIn1−yGaySe2 baselines. On the other hand, y ~ 1 absorbers did not benefit from K introduction. Similar to Cu1−xKxInSe2, the formation of Cu1−xKxGaSe2 alloys was favored at low temperatures and high Na supply by the substrate, relative to the formation of mixed-phase CuGaSe2 + KGaSe2. KIn1−yGaySe2 alloys were grown for the first time, as evidenced by X-ray diffraction and ultraviolet/visible spectroscopy. For all Ga/(Ga+In) compositions, the surface KIn1−yGaySe2 absorbers had superior PV performance in buffered and buffer-free devices. However, the bulk x ~ 0.07 absorbers only outperformed the baselines in buffered devices. The data demonstrate that KIn1−yGaySe2 passivates the surface of CuIn1−yGaySe2 to increase efficiency, VOC, and FF, while bulk Cu1−xKxIn1−yGaySe2 absorbers with x ~ 0.07 enhance efficiency, VOC, and FF by some other mechanism.

Original languageAmerican English
Pages (from-to)362-371
Number of pages10
JournalSolar Energy Materials and Solar Cells
StatePublished - 1 Jun 2018

Bibliographical note

Publisher Copyright:
© 2017 Elsevier B.V.

NREL Publication Number

  • NREL/JA-5K00-70736


  • (Cu,K)GaSe
  • Chalcopyrite
  • Cu(In,Ga)Se
  • K(In,Ga)Se
  • Passivation
  • Potassium


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