DFT-Based Tailoring of the Thermoelectric and Photovoltaic Response of the Halide Double Perovskite Cs₂TlYF₆ (Y = Ag, Co)

The novel material halide double perovskites Cs₂TlYF₆ (Y = Ag, Co) are the potential candidates for thermoelectric and photovoltaic devices. The ground state and temperature dependent electronic transport properties are computed for Cs₂TlYF₆ (Y = Ag, Co) by utilizing density functional theory as employed within WIEN2k package. The negative energy of formation and obtained optimization plots validated the stability of studied halides. The computed electronic properties (band structure, DOS) reveal the semiconductor behavior with band gap value of 1.95 eV and 3.55 eV for Cs₂TlAgF₆ and Cs₂TlCoF₆, correspondingly. The optical features are illustrated in terms of dielectric function \(\varepsilon \left(\omega \right)\) , coefficient of optical absrobance, extinction coefficient, refractive index, and reflectivity. The optimal absorbance in the visible and UV spectrum of light, affirms the materials availability for optoelectronic devices. Thermoelectric characteristics exhibit maximum ZT value, higher Seebeck coefficients and lower thermal conductivity. A ZT of 1.46 at 300 K is attained for Cs₂TlCoF₆, while 0.74 is achieved for Cs₂TlAgF₆. Presented theoretical simulations indicate that the explored materials can of potential usage in renewable energy fields.