Anion Substitution Effects on the Structural, Electronic, and Optical Properties of Inorganic CsPb(I_1–xBr_x)₃ and CsPb(Br_1–xCl_x)₃ Perovskites: Theoretical and Experimental Approaches

Abstract

Several inorganic perovskites of iodine, bromine, and chlorine halides have emerged as candidates for various optoelectronic devices. Highquality CsPb(I 1−x Br x ) 3 and CsPb(Br 1−x Cl x ) 3 (x = 0.00, 0.25, 0.50, 0.75, and 1.00) inorganic perovskite thin films were prepared in this study using a thermal evaporation system. Experiments and first-principles calculations were conducted to elucidate the structural, electronic, and optical properties of the prepared films at room temperature. The thin-film perovskite band gap was tuned from 1.85 to 3.13 eV by replacing I − with Br − and then Cl − . Dominant excitonic effects on the onset of optical absorption led us to explicitly account for enhancing absorption through the Sommerfield factor, enabling us to extract the electronic band gap and the exciton binding energy correctly. We correlated our experimental results with the theory of first principles and gained insight into the lattice parameters, electronic structure, excitonic binding energy (E b ), dielectric constant (ε), and reduced effective mass (μ) of the carriers. With increasing concentration (x) of Br and Cl, the E b increased from 39.44 meV for pure CsPbI 3 to 63.04 and 96.73 meV for pure CsPbBr 3 and CsPbCl 3 , respectively, because of a decrease in the dielectric constant and the almost constant value of μ at ∼0.051 m e . The Urbach energy (E U ) was calculated and found to fluctuate between 28 and 77 meV.

Density Functional Theory Analysis of Structural, Electronic, and Optical Properties of Mixed-Halide Orthorhombic Inorganic Perovskites

“…Table displays the calculated lattice parameters ( a , b , and c ), unit-cell volume ( V ), pressure derivatives ( B ′), bulk modulus ( B ), and total energy ( E ) along with measured and previously predicted values for comparison. Our calculated data are roughly consistent with those measured and previously predicted values, indicating the reliability of the current computational scheme. ,,,,,− Figure S1 shows that as the concentration of Br and Cl increases, the volume of the unit-cell decreases.…”

“…The conduction band minimum (CBM) and valence band maximum (VBM) were found to be localized at the Γ point. Table shows the E g calculated with mBJ-GGA ranging from 1.983 eV for CsPbI 3 to 3.325 eV for CsPbCl 3 , while E g calculated with mBJ + SOC ranges from 1.066 eV for CsPbI 3 to 2.182 eV for CsPbCl 3 , which is consistent with previous theoretical predictions. ,,,,,− Because of its proper band gap of 1.983 eV, CsPbI 3 is suitable for light-absorber applications, whereas CsPbBr 3 and CsPbCl 3 with band gaps of 2.420 and 3.325 eV, respectively, show promising application prospects in solar cells, LEDs, lasers, and photodetectors . Because the E g values with SOC are small in comparison to the experimental results, the alloy formula was used to correct the E g determined by the mBJ-GGA + SOC method ,− where Δ E g (A 1– x B x ) is the change in band gap for the mixed CsPb­(I 1– x Br x ) 3 and CsPb­(Br 1– x Cl x ) 3 perovskites, Δ E g (A) is the change in band gap for pure CsPbI 3 /CsPbBr 3 , and Δ E g (B) is the change in band gap for pure CsPbBr 3 /CsPbCl 3 .…”

Amplified Spontaneous Emission from Thermally Evaporated High-Quality Thin Films of CsPb(Br1–xYx)3 (Y = I, Cl) Perovskites

“…The pattern of pure CsPbBr 3 shows peaks at 15.61, 22.12, 24.58, 25.76, 26.86, 31.12, 34.86, 38.19, and 44.42°, whereas that of pure CsPbCl 3 shows peaks at 16.17, 22.79, 25.82, 32.32, 36.28, 39.79, and 46.29°. Table S1 in the Supporting Information shows the calculated lattice parameters of the perovskite thin films compared with previous studies. ,,− …”

“…The fabrication of perovskite thin films has previously been reported. , To fabricate CsPbI 3 , CsPbBr 3 , and CsPbCl 3 thin films, a 1:1 molar ratio of CsI/PbI 2 , CsBr/PbBr 2 , and CsCl/PbCl 2 were loaded, respectively, into a single boat inside the vacuum chamber of a TES. To tune the structural and optical properties of CsPb­(Br x Y 1– x ) 3 , we mixed perovskites in appropriate CsPbBr 3 /CsPbI 3 and CsPbCl 3 /CsPbBr 3 molar ratios.…”

Progress in the preparation and application of CsPbX3 perovskites

“…7,17,28,[50][51][52][53][54][55][56][57] Zhang et al prepared dense and uniform CsPbX 3 thin films by thermal evaporation and applied them in lasers, LEDs, PSCs, and other photoelectric fields. 1,16,35,[58][59][60][61][62][63][64] In recent years, electrospinning has emerged as a new method to prepare CsPbX 3 . Huang et al encapsulated CsPbX 3 NCs in different polymers and prepared CsPbX 3 nanofibers by electrospinning.…”