Band gap engineering to stimulate the optoelectronic performance of lead-free halide perovskites RbGeX3 (X = Cl, Br) under pressure

First principle studies on structural, electronic, elastic, optical, and thermoelectric properties of XGeCl3 (X = Rb/Cs): Promising compounds for green energy application

“…Using three different approximations (GGA-PBE, TB-mBJ, and HSE06), the band gaps of two compounds, RbGeCl 3 and CsGeCl 3 are calculated as shown in Figure 3. We found that both compounds have direct band gaps (M-M) in the range of 1.26-1.75 eV, which indicates that they are semiconductors, and our results agree with other studies [39][40][41][42][43][44][45][46].…”

“…Figure 6D–F shows the electrical conductivity per relaxation time ( σ / τ ) of both compounds at various temperatures, including 300, 600, and 900 K. For XGeCl 3 (X = Rb/Cs) in the investigated chemical potential range, the value of σ / τ is found to be zero in the chemical range from 0.0 to 1.2 eV, after which it begins to increase with both sides of chemical potential and exhibits opposite behavior above ±1.5 eV [46]. It is noted that the behavior changes to the reverse of increasing with temperature above ±1.3 eV.…”

“…The electronic thermal conductivity of both compounds is found to linearly increase with temperatures up to 900 K, which measures the free electron transport for examined compounds. Low thermal conductivity and high electrical conductivity are characteristics of good thermoelectric materials suggesting optimum thermoelectric response of the XGeCl 3 (X = Rb/Cs) compounds [46, 47]. The computed high‐power factor as represented in Figure 6J–L for the investigated compounds suggests their application in thermoelectric devices.…”

Red shift of lead-free halide perovskite RbCaCl3 under pressure for enhancing optoelectronic performance

“…Hossain et al [37] demonstrated the transition of semiconductor to metallic phase of CsSnBr 3 at high pressure and found an extraordinary shift of absorption edge toward the low energy region under pressure. In addition, the band gap tuning of cubic perovskite chlorides CsYbCl 3 , RbGeCl 3 , and RbSnCl 3 under pressure was observed in recent articles, which significantly enhanced the optical responses responsible for better optoelectronic performance than that exhibited at ambient pressure [45][46][47]. The mechanical behavior of these systems was also remarkably affected by the applied hydrostatic pressure.…”

Enhanced optoelectronic activity of lead-free halide perovskites KMBr3 (M = Ge, Sn) under hydrostatic pressure

“…The pressure applied to perovskites can alter their properties in a range of ways, including the lattice parameter [46], the displacement of cations and anions [47,48], the rotation of octahedral cages [49], phase transitions [50,51], etc For metal halides, pressure normally modifies the physical and chemical properties, such as shrinkage of lattice volume, reduction of the band gap with decreasing the lattice parameter, and enhanced optoelectronic performance [37-39, 42, 44, 45]. In recent works, CsSnCl 3 , RbSnX 3 (X = Cl, Br), AGeI 3 (A = Rb, K), AGeF 3 (A = K, Rb), and RbGeX 3 (X = Cl, Br) exhibit noticeable increments in optical absorption in the visible range under elevated pressure [17,[52][53][54][55]. This phenomenon suggests that it is possible to improve Sn-and Ge-based PSCs by applying hydrostatic pressure.…”