Contemporary development of energy-saving spintronics hinges on the new approach for harnessing spin in semiconductor materials by exploiting the effect of spin–orbit interaction (SOI). In a crystal structures lacking spatial inversion symmetry, the SOI leads to a spin-momentum coupling that breaks Kramer’s degeneracy in electronic bands. Accordingly, the SOI plays an important role for manipulation of electron spin, inducing to numerous novel effects such as spin Hall effect and spin interference . Specifically, Rashba SOI draws much attention originated by its electrical controllability, which is useful for spintronic devices, e.g spin-field effect transistor (S-FET) . For spintronics device operation, materials having strong Rashba SOI are inevitably required, which allows for operating at room temperatures. Therefore, it is crucially important to find a new material that exhibit strong Rashba SOI combined with stable spin-polarized states. One of the new class of materials possessing strong SOI is Hybrid Organic-Inorganic Perovskite (HOIP) , .
Recently, Hybrid Organic-Inorganic Perovskites CH3NH3PbX3 has emerged as a new class of semiconductor materials that demonstrate excellent performance in photovoltaic solar cells . These compounds have been reported to exhibit large and tunable SOI, spin-dependent optical selection rules and the existence of Rashba splitting . In addition, at room temperature, the role of organic cation in crystal structures could directly affect electronic properties and unique spin texture . Furthermore, the intrinsic mechanisms for long carrier lifetime have been proposed in CH3NH3PbI3 . Also, the long spin time has been observed experimentally in polycrystalline films of the HOIP . Therefore, based on such materials, it is possible to extend the functionality of material by exploiting the role of cation and substituting halogen atoms in crystal systems.
Here, we propose to use a substitution of halogen atom for investigating the electronic properties of bulk HOIP CH3NH3PbX3 (X Br, Cl). This paper is focused on the impact of special orientations of organic cation to the spin-splitting characteristic. By using first-principles density functional theory (DFT) calculations, we show that the preferential orientation of organic cation induces the Rashba splitting with anisotropic character of spin polarizations. Also, we found that the unidirectional spin textures are realized in a favored orientation of organic cation aligned along  and  directions. Our analysis using perturbation combined with the symmetry consideration found large spin–orbit strength from these splitting. In addition, on the basis of symmetry analysis, we confirmed that a unidirectional spin texture is preserved in the out-of-plane direction, which indicates the emergence of novel effect called as Persistent Spin Helix (PSH) state. Interestingly, it also suggested that PSH state yield a long spin lifetime, thereby potentially could enhance the performance of perovskite-based spintronic devices.
In this paper, we consider CH3NH3PbBr3 as a prototypical example of the bulk HOIP systems based on cubic crystal structure with a preferential orientation of cation align along the , and directions. We performed first-principles electronic structures calculations on the bulk CH3NH3PbX3 based on density functional theory (DFT) within the generalized gradient approximation (GGA) realized in OpenMX code . We used norm-conserving pseudopotensial  with an energy cut-off at
Results and discussion
Fig. 1(a)–(c) shows the optimized crystal structure of bulk HOIP CH3NH3PbX3 and it is consistent with the model. The calculated values of lattice parameter are summarized in Table 1. Overall, we find that these lattice parameters are in a good agreement with previous calculation. The electronic band structure is performed at high symmetry points of the cubic structures in the Brillouin zone. The chosen k-path is configured by the order of Γ-X-M-Γ-R-X shown in Fig. 1(d).
The band dispersion of CH3
In summary, we have investigated the effect of preferential orientations of organic cation on the electronic properties of the CH3NH3PbBr3 by using the first-principles DFT calculations. We found that the orientation of organic cation has a characteristic of anisotropical Rashba splitting showed by varying spin polarization along - direction. In addition, we revealed that the special orientations of organic cation oriented along and can induce the unidirectional out-of-plane
CRediT authorship contribution statement
Yedija Yusua Sibuea Teweng: Data curation, Formal analysis, Investigation, Software, Validation, Visualization & Writing - original draft. Moh. Adhib Ulil Absor: Conceptualization, Funding acquisition, Methodology, Project administration, Resources, Supervision & Writing - review and editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
This work was supported by PDUPT 2019 Research Grant (N0.2627/UN1.DITLIT/DIT-LIT/LT/2019) funded by the Ministry of Research and Technology and Higher Education (RISTEK-DIKTI), Republic of Indonesia. The computations in this research were conducted using the computer facilities at Universitas Gadjah Mada, Indonesia.
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The effects of organic cation rotation in hybrid Organic-Inorganic Perovskites: A critical review
2022, Materials and DesignSee AlsoThe Difference Between Inorganic & Organic ChemistryDifférences et difficultés – campusleaders.orgOrganique ou Inorganique ? | Passerelle du TexasDégradation inhibée des films à points quantiques à base de pérovskite organique-inorganique via des températures de recuit rapides.
Citation Excerpt :
They thought vdW force is vital for obtaining accurate structure. Besides, Mehdizadeh and SibueaTeweng calculated MAPbX3 (X = Cl, Br, I) systems [26,32]. Javaid et al. used four correlation function GGA + Tkatchenko - Scheffler (TS) correction, GGA + DFT - D3, optB88-vdW and revised PBE for solids to obtain precise lattice constant for different organic cation orientation .
The emergence of hybrid organic–inorganic perovskites (HOIPs) has made great progress in the photovoltaic (PV) field. In recent years, more and more articles have shown that the modification of organic cations can improve HOIPs’ performance, and a surge of interest has been paid to rethink the effect of organic cations. In our review, we summarized the influences of organic cation rotation on structure, optoelectrical properties, and stability. We also provide theoretical insights into why and how organic cations affect the performance of HOIPs in experiments. At last, we have proposed possible control methods and development directions in the hope that the rotation of organic cation can be better observed and utilized in inherently tunable perovskite materials, solar cells, LED, photocatalysis, photothermal conversion, and other related fields.
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