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Crystallographic and Optical Properties of (Cu 1− x Li x ) 2 SnS 3 Photovoltaic Semiconductor
Author(s) -
Nakata Seiya,
Maeda Tsuyoshi,
Wada Takahiro
Publication year - 2019
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201800889
Subject(s) - band gap , monoclinic crystal system , analytical chemistry (journal) , lattice constant , solid solution , ionization energy , valence (chemistry) , materials science , semiconductor , crystallography , chemistry , ionization , crystal structure , diffraction , ion , physics , optics , optoelectronics , organic chemistry , chromatography , metallurgy
In order to clarify a lack of knowledge on lithium alloying with Cu 2 SnS 3 (CTS), the authors synthesized monoclinic (Cu 1– x Li x ) 2 SnS 3 with 0.0 ≤ x ≤ 0.10 and characterized their crystallographic and optical properties. Their lattice constants, a , b , and c increased and angle β decreased with increasing Li content. Two band‐gaps ( E g 1 and E g 2 ) are observed for the (Cu 1 –x Li x ) 2 SnS 3 samples because there is a double onset in the diffuse reflectance spectra. The E g 1 almost linearly increases from 0.91 eV for x = Li/(Li + Cu) = 0.0 to 0.99 eV for x = 0.1 and the E g 2 also linearly increases from 0.99 eV for x = 0.0 to 1.10 eV for x = 0.1. To understand the band diagram of the (Cu 1 –x Li x ) 2 SnS 3 solid solution, the energy level of the valence band maximum (VBM) from the vacuum level is determined from the ionization energy measured by photoemission yield spectroscopy (PYS). The energy levels of VBM for the (Cu 1− x Li x ) 2 SnS 3 solid solution monotonically decreases from −5.18 eV for x = 0.0 to −5.33 eV for x = 0.1 with increasing Li content. On the other hand, the energy levels of the conduction band minimum (CBM) is kept almost constant value by changing Li content. Therefore, the authors consider that the increase in the band‐gap energy of the (Cu 1 –x Li x ) 2 SnS 3 solid solution is mainly caused by lowering the VBM level.