International Journal of Multidisciplinary Research and Publications ISSN (Online): 2581-6187 56 Ahmed Shahzad, Naseeb Ahmad, Muhammad Arbaz, Ifra Shahzadi, Moazama Ahsan, Zia Ur Rehman, Rizwan Akbar, Muhammad Kashif Bashir, Shahbaz Ali, “Exploring the Optoelectronic Potential of Cubic Halide-Perovskite KFeX3 (X = Cl, Br): A DFT Perspective,” International Journal of Multidisciplinary Research and Publications (IJMRAP), Volume 7, Issue 5, pp. 56-62, 2024. Exploring the Optoelectronic Potential of Cubic Halide-Perovskite KFeX3 (X = Cl, Br): A DFT Perspective Ahmed Shahzad 1 , Naseeb Ahmad 2 , Muhammad Arbaz 3* , Ifra Shahzadi 4 , Moazama Ahsan 1 , Zia Ur Rehman 5 , Rizwan Akbar 6 , Muhammad Kashif Bashir 7 , Shahbaz Ali 4* 1 Institute of Physics, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan-64200, Pakistan 2 Department of Physics, Baba Guru Nanak University, Nankana Sahib-39100, Pakistan 3 Department of Chemistry, Institute of Chemical Sciences, Government College University Lahore, 5400, Pakistan 4 Institute of Chemistry, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan-64200, Pakistan 5 School of Energy & Power Engineering, Xi'an Jiaotong University Xi'an, Shaanxi 710049 China 6 Department of Chemistry, COMSATS University Islamabad, Lahore, Pakistan 7 Institute of Physics, The Islamia university of Bahawalpur, 63100, Pakistan Email address: Kashifkarim68@gmail.com Abstract—The present work deals with exploring the electronic, optical, and structural properties of cubic halide-perovskites KFeX3 (X= Cl, Br) through first-principles calculations. The study used the CASTEP code with the PBE exchange-correlation functional in the GGA framework. Ultra-soft pseudo-potential (USP) plane-wave. DFT calculations were carried out for this study. The calculated elastic constants of KFeCl3 and KFeBr3 in their cubic phases supported their mechanical stability. Applying Pugh´s criteria, it is clear that neither of the materials is classified as a brittle material. Electronic band structure analysis indicates that KFeCl3 has an indirect band gap and KFeBr3 possesses a direct band gap, which is consistent with previous reports. Moreover, partial density of states (PDOS) and total density of states (TDOS) were also employed to analyze the electron localization of various bands. Peaks were fitted to the dispersion relation of a hypothetical dielectric function to determine the optical transitions within these compounds. These materials are insulating at 0 K and semiconductors above 0 K rather like the normal BCS metals. The real part of the dielectric function is rather flat with the energy, while the imaginary part of the dielectric function displays a broad spectral width with the energy, which achieves the overall transparency of the inevitable UV-active optoelectronic devices. Keywords— KFeCl3; Density Functional Theory; PDOS; KFeBr3; CASTEP. I. INTRODUCTION To date, perovskite materials have quickly become one of the most exciting materials for research in the field of solar cell technology due to their versatility in properties that could allow them to increase the efficiency of these devices [1]. These materials have optoelectronic properties such as tunable energy band gap, wide absorption band, and a common point defect [2]. Moreover, owing to the large charge diffusion lengths, low carrier effective masses, high-power conversion efficiency (PCE), and high charge carrier mobility of perovskites. Solar energy is the most abundant, cost-effective, and sustainable power source, although the current harnessing of solar energy via traditional photovoltaic technologies remains expensive compared to fossil fuel alternatives. Halide perovskites (ABX3), where A is a cation, B is a Pb 2+ , Sn 2+ , etc., and X is halide have attracted worldwide attention from many different scientific disciplines due to their abundance in nature and high performance [3]. Those materials offer a great range of properties and can be formed into thin films, as well as a variety of smaller structures, such as quantum dots, nanocrystals, nanowires, nanorods, nanoparticles as well as some macroscopic crystals. This makes them very appealing for a variety of different uses. Therefore, the question of whether perovskite cells would ever exceed the traditional silicone-based technology of the decades to come is forefront of everybody's lips [4]. Halide perovskites frequently exhibit temperature-induced structural phase transitions, with different crystallographic phases present in various thermal states including cubic, tetragonal, and orthorhombic forms [5]. Among them, the high-temperature phase is the cubic phase and it is preferred more at high temperatures than other phases. Although perovskites were known long ago, the popularity of perovskites increased substantially after the introduction of perovskite solar cells in 2009 [6]. A widespread surge in halide perovskites occurred in the demand (since 2009) due to the high PCE stability of all photovoltaic cells from 3.8% to 25.2% by 2019. Despite significant strides in research, challenges persist in harnessing halide perovskites for widespread commercial use [7]. These challenges necessitate innovative solutions to address issues such as cost-effectiveness, efficiency, and long- term stability. The current leading halide perovskites, notably those based on methylammonium lead trihalide (MAPbX3, where X can be Cl, Br, or I), incorporate organic components vulnerable to degradation upon exposure to environmental factors like air or moisture, thus compromising their stability [8]. Moreover, the presence of lead in these hybrid perovskites raises environmental concerns, further highlighting the