Exploration, Prediction, and Experimental Verification
of Structure and Optoelectronic Properties in I2‑Eu-IV‑X4 (I = Li, Cu, Ag; IV = Si, Ge, Sn; X = S, Se) Chalcogenide
Semiconductors
posted on 2023-12-18, 21:00authored byTianlin Wang, Timothy M. McWhorter, Garrett C. McKeown Wessler, Yi Yao, Ruyi Song, David B. Mitzi, Volker Blum
Recently,
there has been extensive research into photovoltaic,
thermoelectric, and nonlinear optical applications of chalcogenide
semiconductors within the large set of defect-resistant I2-II-IV-X4 (I = Li, Cu, Ag; II = Ba, Sr, Eu, Pb; IV = Si,
Ge, Sn; X = S, Se) compounds. Five Eu-including compounds have previously
been reported within this family, but a comparative study of possible
structures and electronic properties of all 18 Eu-based combinations
is still absent. Herein, we use hybrid density functional theory to
study rare-earth-including I2-II-IV-X4 semiconductors
with Eu on the II site, in order to further understand this family
and test the geometric tolerance factor approach (reported in our
previous work) as a tool for predicting potential stable structures.
We investigate how the exchange mixing parameter of the HSE06 density
functional, α, affects the energetic positions of electronic
levels, especially of the localized f-electron orbitals near the band
edges of the extended semiconductor structures, using literature photoemission
and band gap data of EuS for comparison. Lowest-energy quaternary
structure candidates, energy band structures, and densities of states
are computationally predicted for all 18 materials. Based on its predicted
photovoltaics-relevant band gap, the previously unknown compound Cu2EuSnSe4 was selected and synthesized. The experimental
structure, lattice parameters, and band gap of Cu2EuSnSe4 are consistent with the computational predictions, confirming
a 1.55 eV band gap.