An in-depth investigation of lead-free KGeCl₃ perovskite solar cells employing optoelectronic, thermomechanical, and photovoltaic properties: DFT and SCAPS-1D frameworks

Abstract

Potassium germanium chloride (KGeCl₃) 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 KGeCl₃ absorber. The positive phonon dispersion curve confirmed the dynamical stability of KGeCl₃. The elastic constant satisfied the Born criteria, validating the mechanical stability and ductility of solid KGeCl₃. The electronic band structure and density of states (DOS) confirmed that the KGeCl₃ 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 KGeCl₃ for solar applications. The Helmholtz free energy (<i>F</i>), internal energy (<i>E</i>), entropy (<i>S</i>), and specific heat capacity (<i>C</i>_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 Ws₂, ZnSe, PCBM, and C₆₀ and HTLs such as CBTS, CdTe, CFTS, Cu₂O, P3HT, and PEDOT:PSS are employed. The highlighted structure, ITO/CBTS/KGeCl₃/Ws₂/Ni, demonstrates remarkable performance with an efficiency of 22.01%, a <i>V</i>_oc of 0.6799 V, a <i>J</i>_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 <i>J</i>-<i>V</i> (current-voltage density) and quantum efficiency (QE) characteristics.