IOSR Journal Of Applied Physics (IOSR-JAP) e-ISSN: 2278-4861.Volume 12, Issue 3 Ser. II (May – June 2020), PP 26-36 www.Iosrjournals.Org DOI: 10.9790/4861-1203022636 www.iosrjournals.org 26 | Page Ab Initio Investigation on the Thermoelectric Properties of γ-CuI for Thermoelectric Device Applications R. Vettumperumal 1* , R. Thangavel 2 , S. Kalyanaraman 3 1 Department of Physics, Fodhdhoo School, Noonu Atoll, Republic of Maldives – 04120. 2 Department of Applied Physics, Indian Institute of Technology, Dhanbad, India - 826004. 3 Sri Paramakalyani College, Alwarkurichi, Tamil Nadu, India – 627425. *Correspondence to: R. Vettumperumal,e-mail: vettumperumalphy@gmail.com. Abstract: Semi-classical transport thermoelectric properties of γ-CuI are investigated using density functional theory (DFT) calculation containing Boltzmann transport equations. The Tran–Blaha modified Becke–Johnson potential (Tb-mBJ) approximation is used as the exchange correlation potential. Thermoelectric properties such as, Seebeck co-efficient, electrical conductivity, thermal conductivity, power factor, figure of merit, thermoelectric voltage and thermoelectric conversion efficiency are discussed with constant relaxation time as a function of chemical potential. This is because the chemical potential is directly related with the carrier concentration and temperature. These parameters are strongly dependent on the doping level and temperature. The maximum range of figure of merit (0.8 – 1.0) and conversion efficiency (93%) is found to be in the range of chemical potential.0.032 – 0.036 Ry. The active thermoelectric region of γ-CuI is observed in the range of temperature from 300 K to 450 K. Hence, γ-CuIbehaves excellent thermoelectric material for heat generation and extraction applications. Keywords: Copper Iodide; Density functional theory; thermoelectric properties; chemical potential. --------------------------------------------------------------------------------------------------------------------------------------- Date of Submission: 16-05-2020 Date of Acceptance: 31-05-2020 --------------------------------------------------------------------------------------------------------------------------------------- I. Introduction Nowadays, the usages of plentiful heat sources (consumer electronics, solar cells, home heater and wearable devices) innear room temperature is tremendously reside in day to life. Harvesting of such energyfrom room temperature range devices has significant interest in the scope of present researchers. Agood thermoelectric material such as heavily doped semiconductors have an energy band gap value (E g ) close to 0.4 eV[1]. Mostly established thermoelectric materials have a tendency to be optically opaque because of their small band gap [2, 3]. Recently, quite a lot ofcategories of non-transparent thermoelectric materials such as tellurides[4], half-Heuslers[5] and silicides[6]were reported with attractive thermoelectric properties for renewable power generation applications. Few optically transparent (E g > 3 eV) thermoelectric devices are known to exist till now, which could be open a new field of novel applicationsin smart windows (or screens), cooling and thermal sensors. In addition to these, it is the fast on-chip cooling and power recovery [7, 8]in optoelectronic devices together with solar cells, infrared photo detectors, as well as fully transparent electronic devices. Transparent thermoelectric material ismostlybeing gooda transparent conductor (TC) with high S and low kvalues.N- and p-type transparent thermoelectric materials are indispensable to manufacture the thermoelectric device. However, the deficiency of highly conductive p-type TCs leads to the recent research has focused on thermoelectric properties of n-type TCs including heavily doped ZnO[9] In 2 O 3 [10] and SrTiO 3 [11]. Among these n-type TCs, Sn-doped In 2 O 3 (ITO) shows the highest value of figure of merit (ZT) ~ 0.14 at room temperature. Conversely, p-type TCs usually exhibit poor electrical conductivities, which is leading to poor thermoelectric performance at room temperature, for example, ZT ~ 0.001 for CuAlO 2 [12] and ZT ~ 0.002 for CuCrO 2 [13]. The p-type misfit-layered oxide Ca 3 Co 4 O 9 was possessing thermoelectric performance (ZT ~ 0.07 at room temperature for single crystal) comparable to the n-type TCs.But, it is not exactly transparent due to its small band gap (E g ~ 2.1 eV) value[14]. Therefore, the lack of p-type transparent thermoelectric materials is the foremostimpediment in comprehension of fully transparent thermoelectric devices. Beginning of 1907, transparent conducting properties of zincblende copper iodide (CuI)was exposed by Bädeker[15, 16]. The wide direct bandgap value of CuI (3.1 eV at room temperature) leads to a high transparency in the visible spectral range and it hasexciton binding energy (62 meV) is similar to that of ZnO[17]. Result of copper vacancies and small effective mass (0.30m 0 ) of the light holes,CuIhas a native p-type conductivity with high hole mobility (>40 cm 2 V −1 ·s −1 in bulk) [18]. It might be possible to improve the hole