Characterization of tetrahedrite Cu10Cd2Sb4S13 monograin materials grown in molten CdI2 and LiI

Highlights: • CdI₂ and LiI as fluxes were used for synthesis-growth of tetrahedrite crystals. • Cu_10-xLi_xCd₂Sb₄S₁₃ solid solution formed if LiI as flux was used. • PL bands with maxima at 1.08 eV (CdI₂-flux) and at 1.16 eV (LiI-flux) were measured. • The thermal quenching E_A of PL bands were 88±6 (CdI₂-flux) and 199±7 meV (LiI-flux). • V_oc = 506 mV, j_sc = 4.46 mA/cm², FF = 50%, η = 1.13% - with tetrahedrite grown in LiI. Synthesis of Cd-substituted tetrahedrite Cu₁₀Cd₂Sb₄S₁₃ (THCd) monograin powders are performed by the molten salt synthesis-growth method using two different fluxes: CdI₂ and LiI. The X-ray diffraction (XRD) data of the materials indicates that mainly single phase of tetrahedrite Cu₁₀Cd₂Sb₄S₁₃ compound is formed in both flux salts. XRD pattern of THCd crystals grown in LiI reveals a shift of all diffraction peaks, lower CdS content and a smaller lattice parameter values in comparison with those formed in CdI₂. Energy dispersive X-ray spectroscopy reveals stoichiometric composition of Cu₁₀Cd₂Sb₄S₁₃ crystals grown in CdI₂ and Cu-poor grown in LiI. Analysis by Atomic Absorption Spectroscopy confirms the incorporation of Li into THCd crystals at the level of 6.7 × 10²⁰ at/cm³. The photoluminescence (PL) study of Cu₁₀Cd₂Sb₄S₁₃ microcrystals at T = 10 K shows single broad asymmetric photoluminescence bands with the maxima at around 1.08 and 1.16 eV for materials grown respectively in CdI₂ and LiI. The thermal quenching activation energy of this PL band is E_A= 88±6 and 199±7 meV for THCd crystals grown in CdI₂ and LiI, respectively. Changes in the lattice parameters, composition and shift in PL maximum give evidences of Li incorporation from LiI into the crystal lattice of THCd forming Cu_10-xLi_xCd₂Sb₄S₁₃ solid solution.