Abstracts Book - IMRC 2018

• SC4-P081
ELECTRONIC STRUCTURE AND OXIDATION STATES ANALYSIS OF
CU2ZNSN(S,SE)4 KESTERITE THIN FILMS OBTAINED BY SPRAY
PYROLYSIS FOR PHOTOVOLTAIC APPLICATIONS
Raquel Garza Hernandez 1 , Holly J. Edwards 2 , James T Gibbon 2 , Vinod R. Dhanak 2 , Francisco
Servando Aguirre Tostado 1
1
Centro de Investigación en Materiales Avanzados, S.C., Laboratorio de Energías Alternas y
Electronica Flexible, Mexico. 2 Stephenson Institute for Renewable Energy, University of
Liverpool, Department of Physics, United Kingdom, Channel Islands & Isle of Man.
For large scale and sustainable PV, the ability to combine cheap, abundant and
nontoxic materials with low cost and low power deposition techniques is
incredibly attractive. A good candidate is Cu2ZnSnS4 (CZTS) which has an optical
band gap (1.4–1.6 eV) and high absorption coefficient (10 4 cm -1 ) suitable for its
use in solar cell as light absorber. This material has reached an efficiency of 8.4%
but it still lesser than the efficiency of CZTSSe (~12.6%). Recently, there have
been efforts to improve the efficiency of CZTSSe solar cells by modifying the S/Se
ratio. In this work, CZTS, CZTSxSey and CZTSe thin films have been deposited by
spray pyrolysis technique on glass substrates. Structural phase identification
was performed using x-ray diffraction (XRD) and Raman spectroscopy. The main
peaks characteristic for kesterite structure were observed in the three
compounds by x-ray diffraction (XRD). The crystallite size for CZTS, CZTSxSey and
CZTSe were 6 nm, 25 nm and 62 nm, respectively, as a result of the incorporation
of selenium in the lattice. The Raman spectra showed the vibrational mode A
(anion vibrations) located on 335 cm -1 and 196 cm -1 attributed to CZTS and
CZTSe, respectively. X-ray photoelectron spectroscopy (XPS) was used to study
the core levels of the constituent elements, surface contaminants, ionization
potential and valence band spectra. The conduction band was determined by
inverse photoemission spectroscopy (IPES). The kesterite thin films are
constituted by Sn 4+ and Cu + confirmed by the Auger parameter. The valence
band is dominated by a mixture of the anion p- and Cu d-orbitals. The Valence
Band Maximum (VBM) of the CZTS, CZTSSe and CZTSe were -0.45 eV, -0.35 eV
and -0.11 eV, respectively. The electronic band gaps obtained XPS and IPES, for
CZTS, CZTSSe and CZTSe were 1.47 eV, 1.2 eV and 1.13 eV, respectively, agree
with the optical bandgap obtained by UV-Vis spectroscopy.