An in-depth investigation of lead-free KGeCl perovskite solar cells employing optoelectronic, thermomechanical, and photovoltaic properties: DFT and SCAPS-1D frameworks

Potassium germanium chloride (KGeCl 3 ) has emerged as a promising contender for use as an absorber material for lead-free perovskite solar cells (PSCs), offering significant potential in this domain. In this study, we conducted a density functional theory (DFT) investigation to analyze and assess the structural, electronic, thermomechanical, and optical characteristics of the cubic KGeCl 3 absorber. The positive phonon dispersion curve confirmed the dynamical stability of KGeCl 3 . The elastic constant satisfied the Born criteria, validating the mechanical stability and ductility of solid KGeCl 3 . The electronic band structure and density of states (DOS) confirmed that the KGeCl 3 material is a semiconductor with a direct band gap of 0.754 eV (GGA) and 0.803 eV (mGGA-RSCAN). The study identified key optical parameters, including absorption, conductivity, reflectivity, dielectric function, refractive index, and loss function, revealing the potential suitability of KGeCl 3 for solar applications. The Helmholtz free energy ( F ), internal energy ( E ), entropy ( S ), and specific heat capacity ( C v ) are computed based on the phonon density of states. Additionally, we investigated twenty-four configurations comprising different combinations of electron transport layers (ETLs) and hole transport layers (HTLs) in SCAPS-1D software. For this purpose, ETLs such as Ws 2 , ZnSe, PCBM, and C 60 and HTLs such as CBTS, CdTe, CFTS, Cu 2 O, P3HT, and PEDOT:PSS are employed. The highlighted structure, ITO/CBTS/KGeCl 3 /Ws 2 /Ni, demonstrates remarkable performance with an efficiency of 22.01%, a V oc of 0.6799 V, a J sc of 41.439 mA cm −2 , and a FF of 78.12%. To analyze photovoltaic (PV) performance, we chose the top four solar cell (SC) configurations. Moreover, a comprehensive examination was conducted to assess the impact of various factors, including the thickness of different layers, capacitance, Mott-Schottky behavior, series and shunt resistance, temperature, and generation-recombination rates, as well as J - V (current-voltage density) and quantum efficiency (QE) characteristics. Crystal structure of KGeCl 3 and the design configuration of the KGeCl 3 -based PSC.