Unraveling the strain-induced and spin–orbit coupling effect of novel inorganic halide perovskites of Ca₃AsI₃ using DFT

The utilization of photovoltaic (PV) technology in the energy sector is notable due to its substantial capacity to displace fossil fuels by diminishing oil consumption, mitigating greenhouse gas (GHG) emission, and mitigating environmental degradation.¹ Silicon (Si), GaAs, CdTe, and Cu(In,Ga)(S,Se)₂ (CIGS) solar cell materials have made tremendous advances in the PV area.^2–5 Because of its high power conversion efficiency (PCE), stability, and radiation hardness, crystalline silicon (Si) takes the lead in their commercialization.^6–8 Traditional solar cells such as Si, however, have limited potential for advancement because of their indirect, suboptimal bandgaps and expensive fabrication processes.⁹ Halide perovskites were introduced in 2009.¹⁰ The remarkable properties of organic–inorganic halide perovskites (OILHPs), such as their reasonable bandgap, ample availability, impressive ability to absorb visible light, decent reflectivity, and affordable manufacturing costs, have generated a great deal of research interest in solar technology.^10–16 Their PCE has increased quickly in the past thirteen years, from 3.8% to 25.8%.^17–20 Unfortunately, the long-term durability issue of OILHPs is currently a major problem because of their susceptibility to moisture, wind, sunlight, and temperature when utilized in a real environment. Moreover, the application and development of perovskite cells on a broad scale are unfortunately restricted by Pb’s low stability, device hysteresis, and toxicity. The three significant obstacles that must be removed before it can be widely commercialized are material toxicity, device hysteresis, and perovskite material stability. Toxic lead needs to be replaced by other nontoxic materials because concerns about the environment arise from the use of such poisonous material.^21–25 Recently, A₃BX₃ type perovskites have attracted great attention due to their exceptional properties such as being a Pb free and direct bandgap material and having mechanical stability and better electronic properties. To date, there have been no comprehensive reports on Ca₃AsI₃. Therefore, a comprehensive study of inorganic Ca₃AsI₃ perovskites is essential for future electronic and optoelectronic device applications.

Numerous investigations have been conducted in recent times using strain engineering, a technique that enables the improvement of specific characteristics of a substance.^26–30 Strain engineering has been identified as a successful method that can modify the configurations and electronic characteristics of organic–inorganic halide perovskites, leading to a better comprehension of the correlation between the structure and properties.^31–37 The study also involved an examination of how pressure affected the structure and bandgap of CsGeBr₃ and CsGeCl₃.^38,39 One way to increase the photovoltaic performance of CaAsI₃ is to restrict its bandgap to within the 1.2–1.4 eV range. If subjected to compressive strain, the inorganic cubic perovskite CsSnCl₃ has the potential to demonstrate remarkable optoelectronic properties by transitioning from a semiconductor to a metallic state.^40,41 Applying either compressive or tensile strain can effectively modify the properties of the bandgap and dielectric function of the CsGeI₃ perovskite.⁴² Modulation of electronic properties in different materials can generally be achieved through the spin–orbit coupling (SOC) effect.^43,44 While light elements exhibit minimal SOC, heavier atoms display a more prominent SOC effect.⁴⁵ The generation of SOC is attributed to the relativistic effect, which causes the alignment of electron spins and the motion of electrons in their orbitals.⁴⁶ As far as we know, no reports have been published to date regarding the electronic and optical characteristics of Ca₃AsI₃ subjected to both strain and SOC. Therefore, a comprehensive study of the effect of strain and SOC on inorganic Ca₃AsI₃ perovskites is essential for future electronic and optoelectronic device applications.

The objective of this study is to use first-principles density-functional theory (FP-DFT) calculations to investigate the structural, electronic, and optical characteristics of cubic Ca₃AsI₃ when subjected to varying levels of strain and SOC. Our investigation involves the use of two different approaches to examine the band structure of Ca₃AsI₃. In our research, we specifically examined the alterations in the bandgap resulting from changes in both strain and SOC, encompassing both increases and decreases. Hence, conducting this research would be advantageous in determining the SOC and strain-specific characteristics of Ca₃AsI₃ inorganic materials and their practical use in next-gen solar cells and energy storage devices.

The analysis of the dynamical stability of material structures and the investigation of optical properties involved the implementation of first-order time-dependent perturbation theory. In order to perform calculations related to the optical properties, a Monkhorst–Pack k-point grid consisting of an 8 × 8 × 8 Γ-centered configuration is employed to sample the Brillouin zone. After that, we analyzed the complex dielectric function to identify the energy range (in eV) in which it exhibits absorption peaks. The real and imaginary parts of the complex dielectric function are added together to obtain ε(ω) = ɛ₁ (ω) + jɛ₂ (ω).

The Ca₃AsI₃ material is depicted in Fig. 1(a) as being a member of the Pm-3m (no. 221) cubic space group.⁵²  Figure 1(a) demonstrates that the unit cell of the structure is composed of seven atoms, with Ca atoms present at 3c (0.5, 0, 0.5) sites, As atoms are situated at 1b (0.5, 0.5, 0.5) sites, and I atoms occupy the 3d (0, 0.5, 0) sites. The first Brillouin zone’s (BZ) k-path is illustrated in Fig. 1(b), with emphasis on the high symmetrical BZ points (Γ-X-M-R-Γ) that are essential for the electronic band structure of Ca₃AsI₃. The band diagram’s recurrence across these points is observed throughout the entire structure. After optimization, the computed lattice parameter for Ca₃AsI₃ was determined to be 6.27 Å, which is considered the most favorable structure.

The density of charges in Ca₃AsI₃ with respect to the (200) crystallographic plane is illustrated in Fig. 2(a) as a 2D map. The colors on the right-hand side of the image’s scale bar indicate the electron density intensity. In Fig. 2(b), there is a depiction of the charge density from a top-down perspective, similar to a bird’s eye view.

This vantage point allows for a clear comprehension of how the charges disperse around the atoms with varying levels of concentration. The charge distribution is illustrated from a 3D perspective in Fig. 2(c). It is evident that the positively charged particles tend to aggregate near the Ca (calcium) atom and the arrangement of charges appears to be uniform. The I (iodine) atom was encircled by a considerable number of negative charges.

As a result of the overlap between the charges of the Ca (calcium) atom and the As (arsenic) atom, it is not feasible to distinguish the As atom individually in the charge density diagram. Consequently, the Ca and As ions developed a covalent bond.^53,54 The charge distribution map provided further evidence that the Ca (calcium) and I (iodine) ions have formed an ionic bond as their charge contours were found to be non-coincidental.^19,54 The ionic bonding mechanism reinforces the bond strength within the structural unit, while the covalent bond between Ca and As ions is leveraged to create a less robust bond. Conversely, As (arsenic) and I (iodine) exhibit antibonding characteristics.

After structural optimization, we computed the electronic band structure and highly symmetric point direction of Ca₃AsI₃. Typically, for a system to be a good candidate for application in optoelectronics devices, a direct bandgap is required.^55–57  Figure 3(a) illustrates the band structures of unstrained Ca₃AsI₃ perovskite formations. In order to interpret the bandgap value from the figure, the Fermi level is fixed at zero. The Γ-X-M-R-Γ path of the cubic structure is being analyzed with respect to the k-axis, and Fig. 3(a) depicts the conduction band minimum (CBM) and valence band maximum (VBM), both of which are situated at the Γ-point.

Based on the results obtained using the PBE function, it can be concluded that the Ca₃AsI₃ material being studied has a direct bandgap structure, with a value of ∼1.58 eV. These findings demonstrate a high level of conformity with the values that were previously documented.³² The evaluation of bandgap using the GGA approach often results in underestimation of its value, which is a well-known drawback of this method. In addition, the LDA+U and LDA methods also found that the bandgap value was underestimated.³³ To overcome this kind of bandgap computation, some researchers have provided a variety of approaches, including the GW method and hybrid functional.^34,35 Furthermore, a direct bandgap is a necessary characteristic that a crystalline substance must possess to be appropriate for advanced photo-thermal and renewable energy purposes. These compounds are considered ideal for efficient solar cells and cells used in photovoltaic applications because of their high value for direct bandgap.

The partial density of states (PDOS), which often depicts the influence of individual atoms and their various states on the bandgap energy of Ca₃AsI₃ formation, usually reflects this. The spread of PDOS for Ca₃AsI₃ structures is shown in Fig. 3(b) in the region of −3 to 3 eV. In Ca₃AsI₃, the places of Ca and As that have been hybridized with I extend across the full energy level while sparing the bandgap. It shows that the primary kind of bonding for Ca–I and As–I is covalent. Moreover, due to significant atomic position variations in Ca₃Asl₃ [Fig. 3(b)] formation, the electron charge was transferred from Ca and As to I. According to the analysis of the cubic phase, it can be said that I-5p orbitals play a significant role in referring to the valence band of every perovskite structure. The main contribution to the conduction band is from the As-4p orbital, whereas the Ca-4s orbital has very little effect.

To perform relativistic calculations, we utilized the PBE functional method to detect the size of the relativistic effect and assess how the heavy element Ca as well as As influences the SOC-included electronic structures of Ca₃AsI₃ perovskites. The impact of SOC on the conduction and valence band regions was significant, leading to changes in the positions of the CBM and VBM, as illustrated in Figs. 4(a) and 4(b). The VBM exhibited significant alterations in its upward shift, while the CBM underwent a downward shift toward the Fermi level. However, the bandgap energy value of Ca₃Asl₃ caused by the SOC is 1.27 eV. Ca₃AsI₃ perovskite structures exhibit a decrease in the bandgap value as a result of the SOC effect. This change in the bandgap is illustrated in Fig. 4(a).

One could obtain a more thorough comprehension of the band construction of cubic Ca₃AsI₃ by investigating the PDOS while considering the influence of the SOC. The inclusion of the SOC effect results in alterations to the conduction and valence bands as a result of the distinct electron influence compared to the PDOS when SOC is not considered. The PDOS illustrated in Fig. 4(b) demonstrates that there is no consistent pattern observed in the impression of the Ca atom when SOC is included. Ca and I atoms have a slight effect on the conduction-band area between 0.635 and 1.75 eV, but the influence of I-5p(j = 0.5) and I-5p(j = 1.5) is noticeable in the valence-band region between −3 and −0.635 eV. The As-4p(j = 0.5) and As-4p(j = 1.5) atoms have a significant impact on the conduction band area between 0.635 and 1.75 eV. However, Ca and I have a smaller effect on the valence-band region between −3 and −0.635 eV.

Investigations were carried out on how strain affected the Ca₃AsI₃ bandgap when incorporating the SOC effect and without it. Ca₃AsI₃ bandgaps scaled between 1.14 and 1.84 eV after the strain was applied in the effective range of −6% to 6% with a 1% space between each value. Figure 5 shows how the Ca₃AsI₃ band topologies change under biaxial compressive and tensile strain. During compressive strain, it is discovered that the VBM and CBM are pushed toward the Fermi level (−6% to 0%) for Ca₃AsI₃ [Figs. 5(a) and 5(b)] but the CBM and VBM are kept at the Γ (gamma) point. When the SOC effect of Ca₃AsI₃ production is taken into consideration, the band configurations under compressive strain are as shown in Fig. 6(a), where Fig. 6(b) shows a magnified view. When compressive strain is applied, the orbital overlap causes a reduction in the length of the Ca, As, and I bonds. Covalent bonding is produced by the orbital overlap because Ca, As, and I are strongly hybridized when incorporating the SOC effect and without it. The bandgap is shown to decrease with increasing compressive strain (i.e., incorporating the SOC effect and without it). As shown in Fig. 5(c) for Ca₃AsI₃, the electronic band structure similarly varies when subjected to tensile strain (0%–6%). The bandgap may widen under tensile tension because the VBM and CBM have been moved from the Fermi level. To enable a lowered force between the atoms of Ca, As, and I, the bond length and atomic distance between the atoms are enhanced. The bandgap ultimately widens for the Ca₃AsI₃ structure under tensile tension, which is shown in a magnified view in Fig. 5(d). The gamma point (Γ-point) under compressive and tensile strain, incorporating the SOC effect and without it, is shown in a magnified view in Figs. 6(b), 5(b), 6(d), and d5(d).

The changes in the bandgap for Ca₃AsI₃ structures when subjected to compressive and tensile strains, incorporating the SOC effect and without it, are presented in Table I and Fig. 7 for reference. According to these findings, the bandgap reduces virtually linearly as compressive strain increases (incorporating the SOC effect and without it), but it increases linearly when tensile strain increases (Fig. 7). Surprisingly, Ca₃AsI₃ continues to be a direct-bandgap semiconductor throughout the whole strain region. Ca₃AsI₃ has a bandgap between 1.3 and 1.4 eV for both compressive strain (without SOC) and tensile strain (with SOC). Based on the Shockley–Queisser hypothesis, it is proposed that this structure will perform the best in terms of photovoltaics under these circumstances.⁵⁹ 

Furthermore, the orbital distributions of the particles (Ca, As, and I) change as strain is introduced. Figures 8(a)–8(c) show the PDOS of Ca₃AsI₃ under compressive strain, while Figs. 8(d)–8(f) demonstrate the PDOS under tensile strain. Figures 8(a)–8(c) show the PDOS of Ca₃AsI₃ under compressive strain, while Figs. 8(d)–8(f) demonstrate the PDOS under tensile strain, Fig. 8 shows the PDOS incorporated with the SOC effect. As the strain transitions from −6% to +6%, the partial density of states (PDOS) related to the 5p orbital of the I atoms shows a nearness to the valence band side, which is positioned below the Fermi level. The density of states (DOS) within the conduction band region is greatly influenced by the presence of the 4p orbital of the As atoms. While the static position and structure of the occupied density of states (DOS) for the As-4p orbital remain unchanged on the conduction band side, the total contribution to the DOS increases as the applied strain is varied between −6% and +6%. The figure makes it evident that a higher tensile strain results in an increased total density of states (DOS) for the Ca₃AsI₃ structure. Specifically, there is a shift from around 18.5 electrons/eV at −6% strain to about 30 electrons/eV at +6% strain. Except for the bandgap region, hybridized orbitals of Ca–As and Ca–I can be seen across the entire energy range.

To obtain a precise estimation of the band structure, the computation takes into account the SOC effect. Figures 9(a)–9(f) indicate that the SOC effect is significant in both the conduction and valence band regions, particularly when there are fluctuations in the levels of the conduction band minimum (CBM) and valence band maximum (VBM). The 5p(j = 0.5) and 5p(j = 1.5) orbitals of the I atom exhibit activity near the valence band side, positioned slightly near the Fermi level. Similarly, closer to the Fermi level, the 4p(j = 0.5) and 4p(j = 1.5) orbitals of the As atom exhibit activity toward the conduction band side. Thus, the As atom’s 4p orbitals dominate the total DOS in the conduction band section.

Taking the SOC effect into account, the performance of the total density of states (TDOS) increases as the applied strain is altered from −6% to +6%. Figure 9 shows that when taking the SOC effect into account, the total density of states (TDOS) for the Ca₃AsI₃ configuration is 14 electrons/eV at a strain of −6% and 19 electrons/eV at a strain of +6%. Figures 10(a) and 10(b) illustrate the TDOS of Ca₃AsI₃ for different biaxial compressive and tensile stresses, taking into account or disregarding the influence of spin–orbit coupling (SOC). The TDOS can assist us in comprehending the electronic band structure behavior of Ca₃AsI₃. When not subjected to strain, the contribution of the I atom's orbitals to the total density of states (TDOS) of the valence band below the Fermi level (E_F) is considerable, while the impact of the Ca-4s, Ca-3p, and As-3d orbitals is minimal, regardless of the consideration of the SOC effect.

Conversely, the contribution of the As atom's orbitals to the TDOS of the conduction band above E_F is significant, while the impact of the Ca-4s, Ca-3p, and I-5p orbitals is negligible, regardless of the consideration of the SOC effect. The presence of a gap in the TDOS around the Fermi level signifies the semiconducting nature of the material and draws attention to its bandgap properties.³¹ When subjected to compressive strains ranging from −6% to 0%, the TDOS line of Ca₃AsI₃ shifts closer to the Fermi level. This occurs regardless of whether the SOC effect is taken into account or not, and it causes an enhancement in the material’s conductivity. Conversely, under tensile strains (0% to +6%), regardless of whether the SOC effect is taken into account or not, the TDOS line moves away from the Fermi level, causing a decrease in the conductivity of Ca₃AsI₃ materials. Based on a detailed examination of the band structure and TDOS of Ca₃AsI₃, there is a prediction of a transition occurring in the bandgap.

The Kramers–Kronig transformation is employed to derive the real part of the dielectric function,⁶⁰ while the components of the momentum matrix are used to calculate the imaginary part of the dielectric function.⁶¹ 

By analyzing the real part of the dielectric constant, one can acquire knowledge about polarization and dispersion effects.^62,63 A value of 7.98 is obtained for ɛ₁ (0) of cubic Ca₃AsI₃ through calculation. In Fig. 10(a), it can be observed that the real part ɛ₁ (0) of the dielectric function displays pronounced absorption peaks close to photon energies, particularly at ∼2.1 and 3.2 eV. In the Ca₃AsI₃ structure, the real part values of ε₁(ω) follow a trend of rising from ε₁(0), peaking, and then declining to form multiple peaks. The magnitude and location of these peaks are affected by variations in the biaxial strain. Typically, materials characterized by high bandgap values demonstrate lower peak values of a dielectric constant than their low bandgap counterparts.⁶⁴  Figure 10(b) shows that compressed under force, the peak of the dielectric constant in the Ca₃AsI₃ structure was shifted to a lower photon energy (redshift) due to a reduction in the bandgap. An increase in tensile strain resulted in a lower peak in the dielectric constant of the Ca₃AsI₃ structure, which shifted toward a higher photon energy (blueshift).

The peaks detected in the imaginary part of the dielectric function are a result of carrier transitions occurring between the valence and conduction bands.⁶⁵ The imaginary part ɛ₂ (ω) of a system is closely linked to its band structure. The principal peak in ɛ₂ (ω) occurs at a photon energy of 3.6 eV, as shown in Fig. 10(c), which corresponds to the highest optical point of 5.93 for cubic Ca₃AsI₃. The data obtained from the Ca₃AsI₃ compound imply that its maximum peaks fall within the visible and infrared range, likely due to its narrowness. Figure 11(d) demonstrates that the application of strain results in the enlargement and displacement of the dielectric function’s imaginary portion near the long wavelength region. Roughly speaking, the imaginary portion of the Ca₃AsI₃’s spectrum can be categorized into two distinct regions: a lower energy range spanning from 2.1 to 4.7 eV and a higher energy range spanning from 5.3 to 7.8 eV. The absorption peaks present in the imaginary portion of the spectrum have a significant impact on the valence-to-conduction band shift of charge carriers. The displacement of these peaks can be attributed to variations in the lattice constant and bandgap.

A redshift and blueshift in the imaginary peaks are displayed under compressive and tensile strains, respectively, as demonstrated in Fig. 11(d). Based on our findings, the Ca₃AsI₃ perovskite material being studied could potentially exhibit an adjustable absorption spectral region under biaxial compressive and tensile strains. Furthermore, we observed that the imaginary dielectric component becomes zero beyond 8 eV photon energy, indicating the material’s higher optical transparency and lower optical absorption. The potential of a material to attain high solar PCE is significantly influenced by its ability to absorb light energy,³⁴ and the optical absorption coefficient is a key parameter that supports this.³⁶ Across all configurations, analogous features can be observed between the profile of the optical absorption coefficient and the imaginary portion of the dielectric constant.⁵⁴ In Ca₃AsI₃, the optical absorption spectra exhibit the maximum peak in the visible zone.⁶⁶ 

Figures 12(a) and 12(b) display the absorption coefficient of Ca₃AsI₃ in terms of photon energy for both unstrained and various biaxially strained conditions. The absorption edge undergoes a considerable displacement toward the blue region of the spectrum in the presence of tensile strain and a notable shift toward the red end of the spectrum when there is compressive strain. In structures, the absorption coefficient in the visible light territory is increased by compressive strain, in comparison to the unstrained system. For systems that are subjected to tensile strain, the opposite is observed. The strain-induced alteration in the absorption of the Ca₃AsI₃ is in line with the anticipated bandgap. If the compressive strain is augmented, the absorption coefficient in the visible range of the Ca₃AsI₃ structure increases, and this property is beneficial for the development of solar cells. The Ca₃AsI₃ compound experiences a reduction in the absorption coefficient in the visible light territory when subjected to increased tensile strain.

The light-responsive characteristics of a substance can be examined by studying the energy dissipation of an electron,³⁴ denoted as L(ω). It determines the extent of energy loss that occurs within a medium or substance during propagation. In case the energy level of a released photon exceeds the material’s bandgap, then a peak in the plot of L(ω) for Ca₃AsI₃ indicates a loss of energy. Figure 12(d) illustrates that the cubic structure of Ca₃AsI₃ exhibits peaks in the range of 7–10 eV in the plot of L(ω), and the unstrained state is indicated in Fig. 12(c). If the energy is below the bandgap, then there is no scattering that can be detected. The loss function for photon energy in the strained Ca₃AsI₃ material is observed up to 10 eV. As shown in Fig. 12(d), the optical loss of Ca₃AsI₃ has been estimated under different biaxial compressive and tensile strain conditions. The findings suggest a redshift, which indicates a considerable shift toward the direction of lower photon energies. The application of compressive strain results in an optical loss variation in all structures. Within the visible light spectrum, the optical losses of the Ca₃AsI₃ structure are greater under tensile strain rather than under compressive strain.

Compressive strain 0–6 is clearly discussed in this article. Now we discuss how much strain should be applied on Ca₃AsI₃ to change its phase and how it is changes the behavior from semiconductor to metallic-phase. As the compressive strain increases (incorporating the SOC effect and without it), both the valence band maximum (VBM) and conduction band minimum (CBM) progressively move closer to the Fermi level, resulting in a reduction in the energy bandgap.^43,67–69 When the compressive strain increases (incorporating the SOC effect and without it) from 0% to 15%, the band structure analysis reveals a notable decrease in the direct bandgap of the Ca₃AsI₃ perovskite material, decreasing from 1.58 to 0 eV (without SOC) and 1.27–0 eV (with SOC).

The band structure displays a metallic feature in Figs. 13(d)–13(f) when the compression reaches the critical value of 15% (without SOC) and 12% (with SOC). Upon reaching the critical value of 15% and 12% of compression, the band structure exhibits a distinct metallic characteristic, illustrated in Figs. 13(d) and 13(e), providing clear evidence of a robust transition from a semiconductor to a metal phase. Similar trends have been occurred in CsSnBr₃, CsSnCl₃ and other perovskites.^40,67,68

Through the analysis of the density of states (DOS), researchers have gained a more comprehensive understanding of the metallic behavior of Ca₃AsI₃ under compressive strains incorporating the SOC effect and without SOC.⁴⁰  Figure 14 illustrates the partial density of states (PDOS) of the Ca₃AsI₃ perovskite at various applied compressive strains incorporating the SOC effect and without SOC. At 12% (with SOC) and 15% (without SOC) strain, there is an increase in the contribution of the I-5p orbital, which becomes more prominent near both the valence and conduction bands. A material is considered metallic when there is a non-zero value of density of states (DOS) at the Fermi level.^70,71 At 12% compressive strain (with SOC) and 15% compressive strain (without SOC), the TDOS exhibits a noteworthy non-zero value, indicating a semiconductor to metallic transition in the Ca₃AsI₃ metal halide at the specific pressure points shown in Figs. 14(d) and 14(e). The observation of a significant DOS at the Fermi level, particularly evident at 12% (with SOC) and 15% (without SOC) and showing an increasing trend with increasing compressive strain, strongly suggests a semiconductor to metallic transition in the Ca₃AsI₃ metal halide under high-compressive strain conditions. The comprehensive examination of the band structure and density of states in this study supports the prediction of the semiconductor to metallic transition in Ca₃AsI₃ under compressive strain. Therefore, it is essential to conduct future experimental investigations to precisely determine the transition pressure for the semiconductor to metal transition in Ca₃AsI₃.

This study utilized first-principles DFT calculations to examine the electrical, optical, and structural properties of the inorganic material Ca₃AsI₃. The computed lattice parameter of 6.27 Å for Ca₃AsI₃ indicates the most favorable structure. The structure of Ca₃AsI₃ was found to have a direct bandgap value of 1.58 eV. Taking the SOC effect into account causes a decrease in the electronic bandgap of Ca₃AsI₃ to 1.27 eV. The bandgap exhibits a decrease with an increase in the level of compressive strain applied, regardless of whether the SOC effect is considered or not. Conversely, the bandgap increases as the induced tensile strain increases. According to the PDOS analysis, the electronic states responsible for the formation the valence band and conduction band in Ca₃AsI₃ primarily originate from the orbitals of As and I atoms rather than from those of Ca. Under a range of strain conditions spanning from −6% to +6%, the characteristics concerning light absorption and loss, along with the dielectric function of Ca₃AsI₃, were thoroughly examined. According to our research, the strain-driven optical characteristics of Ca₃AsI₃ exhibit absorption peaks (blue-shift and red-shift) close to the ultraviolet to visible spectrum at various induced stresses. In addition, applying compressive strain causes the peak of the Ca₃AsI₃ dielectric constant to shift to a lower photon energy (redshift). However, applying higher levels of tensile strain causes it to shift to a higher photon energy (blueshift). On the other hand, in the visible light spectrum, the optical losses of the Ca₃AsI₃ structure are greater under tensile strains rather than under compressive strains. The outcome of this research has the potential to enable further investigations into the application of Ca₃AsI₃ in photovoltaic and optoelectronic devices.

The authors are grateful to the Department of Electrical and Electronic Engineering, Begum Rokeya University, Rangpur 5404, Bangladesh, for permitting them to use the advanced energy materials and the solar cell research laboratory.

The authors have no conflicts to disclose.

Md. Ferdous Rahman: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Resources (equal); Software (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Md. Azizur Rahman: Data curation (equal); Formal analysis (equal); Methodology (equal); Resources (equal); Software (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Md. Rasidul Islam: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Investigation (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Avijit Ghosh: Data curation (equal); Formal analysis (equal); Resources (equal); Software (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Md. Abul Bashar Shanto: Data curation (equal); Formal analysis (equal); Resources (equal); Software (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Mithun Chowdhury: Data curation (equal); Formal analysis (equal); Resources (equal); Software (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Md. Al Ijajul Islam: Data curation (equal); Resources (equal); Software (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Md. Hafizur Rahman Data curation (equal); Formal analysis (equal); Resources (equal); Software (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). M. Khalid Hossain: Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). M. A. Islam: Data curation (equal); Formal analysis (equal); Resources (equal); Software (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal).

The data that support the findings of this study are available from the corresponding author upon reasonable request.