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Open Access Publications from the University of California

Electron-Selective TiO 2 Contact for Cu(In,Ga)Se 2 Solar Cells

  • Author(s): Hsu, W
  • Sutter-Fella, CM
  • Hettick, M
  • Cheng, L
  • Chan, S
  • Chen, Y
  • Zeng, Y
  • Zheng, M
  • Wang, HP
  • Chiang, CC
  • Javey, A
  • et al.

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The non-toxic and wide bandgap material TiO 2 is explored as an n-type buffer layer on p-type Cu(In,Ga)Se 2 (CIGS) absorber layer for thin film solar cells. The amorphous TiO 2 thin film deposited by atomic layer deposition process at low temperatures shows conformal coverage on the CIGS absorber layer. Solar cells from non-vacuum deposited CIGS absorbers with TiO 2 buffer layer result in a high short-circuit current density of 38.9 mA/cm 2 as compared to 36.9 mA/cm 2 measured in the reference cell with CdS buffer layer, without compromising open-circuit voltage. The significant photocurrent gain, mainly in the UV part of the spectrum, can be attributed to the low parasitic absorption loss in the ultrathin TiO 2 layer (∼10 nm) with a larger bandgap of 3.4 eV compared to 2.4 eV of the traditionally used CdS. Overall the solar cell conversion efficiency was improved from 9.5% to 9.9% by substituting the CdS by TiO 2 on an active cell area of 10.5 mm 2. Optimized TiO 2 /CIGS solar cells show excellent long-term stability. The results imply that TiO 2 is a promising buffer layer material for CIGS solar cells, avoiding the toxic CdS buffer layer with added performance advantage.

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