title: Electron-Selective TiO2 Contact for Cu(In,Ga)Se2 Solar Cells.
abstract: The non-toxic and wide bandgap material TiO2 is explored as an n-type buffer layer on p-type Cu(In,Ga)Se2 (CIGS) absorber layer for thin film solar cells. The amorphous TiO2 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 TiO2 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 TiO2 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 TiO2 on an active cell area of 10.5 mm(2). Optimized TiO2/CIGS solar cells show excellent long-term stability. The results imply that TiO2 is a promising buffer layer material for CIGS solar cells, avoiding the toxic CdS buffer layer with added performance advantage.
authors.affiliation: Electrical Engineering and Computer Sciences Department, University of California, Berkeley, CA 94720.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.|Green Energy &Environment Research Laboratorie, Industrial Technology Research Institute, 31040, Hsinchu, Taiwan, R.O.C.
authors.forename: Weitse
authors.initials: W
authors.lastname: Hsu
authors.affiliation: Electrical Engineering and Computer Sciences Department, University of California, Berkeley, CA 94720.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
authors.forename: Carolin M
authors.initials: CM
authors.lastname: Sutter-Fella
authors.affiliation: Electrical Engineering and Computer Sciences Department, University of California, Berkeley, CA 94720.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
authors.forename: Mark
authors.initials: M
authors.lastname: Hettick
authors.affiliation: Green Energy &Environment Research Laboratorie, Industrial Technology Research Institute, 31040, Hsinchu, Taiwan, R.O.C.
authors.forename: Lungteng
authors.initials: L
authors.lastname: Cheng
authors.affiliation: Green Energy &Environment Research Laboratorie, Industrial Technology Research Institute, 31040, Hsinchu, Taiwan, R.O.C.
authors.forename: Shengwen
authors.initials: S
authors.lastname: Chan
authors.affiliation: Green Energy &Environment Research Laboratorie, Industrial Technology Research Institute, 31040, Hsinchu, Taiwan, R.O.C.
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Electrical Engineering and Computer Sciences Department, University of California, Berkeley, CA 94720.
authors.forename: Yuping
authors.initials: Y
authors.lastname: Zeng
authors.affiliation: Electrical Engineering and Computer Sciences Department, University of California, Berkeley, CA 94720.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
authors.forename: Maxwell
authors.initials: M
authors.lastname: Zheng
authors.affiliation: Electrical Engineering and Computer Sciences Department, University of California, Berkeley, CA 94720.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
authors.forename: Hsin-Ping
authors.initials: HP
authors.lastname: Wang
authors.affiliation: Green Energy &Environment Research Laboratorie, Industrial Technology Research Institute, 31040, Hsinchu, Taiwan, R.O.C.
authors.forename: Chien-Chih
authors.initials: CC
authors.lastname: Chiang
authors.affiliation: Electrical Engineering and Computer Sciences Department, University of California, Berkeley, CA 94720.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
authors.forename: Ali
authors.initials: A
authors.lastname: Javey