cm7b04010_si_004.cif (1.48 kB)
Polymorphism in Cu2ZnSnS4 and New Off-Stoichiometric Crystal Structure Types
dataset
posted on 2017-10-30, 00:00 authored by Christopher
J. Bosson, Max T. Birch, Douglas P. Halliday, Chiu C. Tang, Annette K. Kleppe, Peter D. HattonCu2ZnSnS4 (CZTS) is a very promising material
for the absorber layer in sustainable thin-film solar cells. Its photovoltaic
performance is currently limited by crystal structure disorder, which
causes fluctuations in electrostatic potential that decrease open-circuit
voltage. The origin of this disorder is still not fully understood.
This work investigates five samples of CZTS over a range of compositions,
fabricated by solid-state reaction. Their crystal structures are conclusively
identified using high-resolution anomalous X-ray diffraction. Three
of the samples display two distinct CZTS phases, evident in minute
splitting of some diffraction peaks (by ∼0.02°) due to
different c/a lattice parameter
ratios. These are attributed to different composition types of CZTS,
defined by different charge-neutral defect complexes. In addition
to such types previously reported, two new types are proposed: G-type,
in which [2CuSn3– + CuZn– + Cui+ + 3VS2+] defects are prevalent, and H-type, in which [3Si2– + VCu– + ZnCu+ + 2SnCu3+] defects are
prevalent. In both cases, the defects probably do not form a single
complex due to their large number. Above the order–disorder
phase transition the two CZTS phases generally converge to a single
phase. A mechanism of phase formation in CZTS is thus proposed. This
is the first time CZTS crystal structures have been investigated with
sufficiently high resolution to distinguish these different CZTS phases,
thereby establishing polymorphic behavior in CZTS.