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The Earth Abundant Thin Film Photovoltaic Cu2 ZnSn(Sx Se1-x)4 (CZTS,Se) : Electronic Properties and Buffer-Layer Band Alignments

Event Details

Event Dates: 

Thursday, August 15, 2013 - 11:00am

Seminar Location: 

  • JILA X317

Speaker Name(s): 

Richard Haight

Speaker Affiliation(s): 

IBM TJ Watson Research Center
Seminar Type/Subject

Scientific Seminar Type: 

  • JILA Public Seminar

Event Details & Abstract: 

CZTS,Se is an earth abundant thin film photovoltaic material that can be deposited by evaporation of the individual elements or spun on from the solution phase. Solution phase deposition is unique in that it is the most commercially viable fabrication method and, at IBM has yielded world record efficiencies exceeding 11%. In this talk I will describe studies of the electronic properties of CZTS,Se fabricated from both methods. In particular, using femtosecond ultraviolet photoelectron spectroscopy (fs-UPS) in addition to other characterization techniques, we have been able to extract key electronic properties of the CZTS,Se surface and its interfaces with n-type buffer materials (the p-n junction). These electronic parameters include Fermi level position and band bending in the CZTS,Se, conduction and valence band offsets with CdS and Cd-free buffer layers and ionization potentials, which we correlate with device measurements. While the closed circuit current, Jsc of our devices has improved dramatically and is close to its theoretical limit, increasing the open circuit voltage, Voc has proven problematic. This limitation is related to fundamental defects in CZTS,Se and I will describe experimental and theoretical results that provide key insight into this problem.