Crystal growth, electronic and optical properties of Tl2CdSnSe4, a recently discovered prospective semiconductor for application in thin film solar cells and optoelectronics

Insights from Experiment and Theory on Peculiarities of the Electronic Structure and Optical Properties of the Tl2HgGeSe4 Crystal

“…With the aim of evaluating peculiar features of population by electronic states of the valence band area of the Tl 2 HgGeSe 4 crystal and the nature of its energy band gap, we carry out first-principles DFT computation of the electronic structure of this compound. Recent data dealing with DFT computation of several quaternary chalcogenides belonging to the Cu­(Tl) 2 B II D IV X 4 -type series present ,,,, that it is necessary to treat different models to achieve a good agreement of theoretical and experimental results. This fact is explained by the fact that the generally employed GGA-PBE technique fails in many cases when using for XC potential in calculations of the Cu­(Tl) 2 B II D IV X 4 -type compounds.…”

“…The system energy scale was calibrated by employing reference pure etalon gold and copper metals as reported elsewhere . It should be noted that, in the case of XPS studies of Cu­(Tl) 2 B II D IV X 4 -type sulfides and selenides, the charging surface effects are generally overcome by measuring the reference core-level C 1s line originated from a thin layer of adsorbed hydrocarbon by adjusting its binding energy (BE) to 284.6 eV. , However, when employing a Mg Kα X-ray source to excite the XPS spectra of Ge-bearing compounds, there is a superposition of the hydrocarbon C 1s spectrum with the neighboring auger Ge L 2 M 23 M 23 line . As a result, in the present experiments, the charging surface effect has been compensated by using a specially constructed flood gun available in the SPECS UHV analysis system as we used to do such a technique in the case of Ge-bearing Cu­(Tl) 2 B II D IV X 4 -type chalcogenides. ,, Following the findings on the electronic structure of quaternary Ge-bearing selenides Cu­(Tl) 2 B II GeSe 4 indicating that among electronic states associated with these atoms one could expect essential input of Se­(Ge) 4p-like states in the valence band area, ,, we have recorded the fluorescent XES Se­(Ge) Kβ 2 spectra originating due to the transition from the N II,III shell to the K level and supplying information regarding the peculiarities of energy distributions of valence Se­(Ge) p-like electronic states. , The latter bands were derived with a DRS-2 M spectrometer in the third order of reflection and employing for spectral excitation a BHV-7 X-ray tube with a Au anode.…”

“…We used a grid amounting to 1000 k -points for Brillouin zone sampling via its irreducible wedge. The computing iterations were carried out until reaching the condition q = ∫|ρ n – ρ n –1 | d r ≤ 10 –4 , where ρ n ( r ) and ρ n –1 ( r ) are ascribed to the charge density of the present and previous iterations, respectively, as it is generally proposed to follow in the case of (Cu,Tl) 2 B II D IV X 4 -type sulfides and selenides. ,,,, …”

“…Following the fact that the detailed insight on the electronic band structure is a primary key for predicting suitable routes of modification of the physical/chemical properties of solids to a desired technological request, the electronic band structure computing data and/or X-ray spectroscopy investigations were gained recently for Tl 2 HgSnS 4 and Tl 2 B II D IV Se 4 (B II = Cd and Hg and D IV = Ge and Sn) compounds. − These results allow for a statement that the contribution of electronic p-like states associated with S­(Se) atoms prevails in their valence band area, and contributions of Tl 6s states prevail near the valence band bottom. The Tl 2 HgSnS 4 and Tl 2 B II D IV Se 4 (B II = Cd and Hg; D IV = Ge and Sn) chalcogenides are direct gap materials. − …”

Single-phase CZTSe via isothermal recrystallization in a KI–KCl flux

“…Quaternary chalcogenides with the general formula A 2 B II C IV X 4 (A -Cu, Ag; B -Zn, Cd, Hg, Fe; C -Sn, Ge, Si; X -S, Se) are known to be promising compounds for various photovoltaic devices. [1][2][3][4] Among these, compounds with the kesterite structure, Cu 2 ZnSnSe 4 and Cu 2 ZnSnS 4 (hereafter noted as CZTSSe), and their solid solutions have attracted great attention as alternatives to CIGSSe (Cu, In) Ga (S, Se) 2 -based thin films to be used as an adsorbing layer in solar panels. Despite recent achievements in the engineering of CIGSSe solar cells with an efficiency above 20%, they are commercially and environmentally unpromising due to the shortage of In and Ga and, consequently, the high cost of the end product.…”