The effect of chemical-composition modification on the chiroptical property of chiral organic ammonium cation-containing organic inorganic hybrid perovskite (chiral OIHP) is investigated. Varying the mixing ratio of bromide and iodide anions in Sor R-C 6 H 5 CH 2 (CH 3 )NH 3 ) 2 PbI 4(1−x) Br 4x modifies the band gap of chiral OIHP, leading to a shift of the circular dichroism (CD) signal from 495 to 474 nm. However, it is also found that an abrupt crystalline structure transition occurs, and the CD signal is turned off when iodide-determinant phases are transformed into the bromide-determinant phase. To obtain CD in the wavelength range where the bromide-determinant phase is supposed to exhibit chiroptical activity, that is, <474 nm, Sor R-C 12 H 7 CH 2 (CH 3 )NH 3 with a larger spacer group can be adopted; thus, the CD signal can be further blue-shifted to ∼375 nm. Here, we show that chemical-composition modification of chiral OIHP affects the chiroptical properties of chiral OIHP in two ways: (1) tuning the wavelength of CD by modulating the excitonic band structure and (2) switching the CD on and off by inducing a crystalline-structure change. These properties can be utilized for structural engineering of high-performance chiroptical materials for spin-polarized light-emitting devices and polarization-based optoelectronics.

Silver nanowire (AgNW)‐based transparent electrodes prepared via an all‐solution‐process are proposed as bottom electrodes in flexible perovskite solar cells (PVSCs). To enhance the chemical stability of AgNWs, a pinhole‐free amorphous aluminum doped zinc oxide (a‐AZO) protection layer is deposited on the AgNW network. Compared to its crystalline counterpart (c‐AZO), a‐AZO substantially improves the chemical stability of the AgNW network. For the first time, it is observed that inadequately protected AgNWs can evanesce via diffusion, whereas a‐AZO secures the integrity of AgNWs. When an optimally thick a‐AZO layer is used, the a‐AZO/AgNW/AZO composite electrode exhibits a transmittance of 88.6% at 550 nm and a sheet resistance of 11.86 Ω sq−1, which is comparable to that of commercial fluorine doped tin oxide. The PVSCs fabricated with a configuration of Au/spiro‐OMeTAD/CH3NH3PbI3/ZnO/AZO/AgNW/AZO on rigid and flexible substrates can achieve power conversion efficiencies (PCEs) of 13.93% and 11.23%, respectively. The PVSC with the a‐AZO/AgNW/AZO composite electrode retains 94% of its initial PCE after 400 bending iterations with a bending radius of 12.5 mm. The results clearly demonstrate the potential of AgNWs as bottom electrodes in flexible PVSCs, which can facilitate the commercialization and large‐scale deployment of PVSCs.

with different substances; therefore, the resulting change in polarization state can reveal the chemical configuration, [6] structural conformation, [7] and optoelectronic properties of a substance. [8] This chiroptical phenomenon and interpretation of chiral characteristics constitute the basis of chiral photonics. In particular, circularly polarized photoluminescence (CPPL) (i.e., differential emission of left-handed circularly polarized (LCP) and righthanded circularly polarized (RCP) lights) is absolutely necessary for scrutinizing the ground state of materials, [9] whereas circular dichroism (CD) spectroscopy (i.e., differential absorption of LCP and RCP lights) can provide useful information regarding the structure of the excited state of materials. [7] These complementary phenomena enable the development of advanced smart photonic technologies.A material is chiral if it cannot be superimposed on its mirror image. This phenomenon is commonly observed in natural organic compounds, such as small amino acids, saccharide, starch, and DNA. Owing to their noncentrosymmetric structure (e.g., no inversion symmetry, mirror plane, and glide plane), chiral materials exhibit nonlinear optical responses to CPL in CD and CPPL spectra. Although organic chiral materials are ubiquitous and exhibit strong chiroptical activity in the near-UV region, [10] the structural softness of organic chiral molecules makes them difficult to stack, resulting in poor charge transfer capability in practical polarization-based optoelectronic devices. Additionally, in chiral photonics research, focus should be on stable and broad wavelength tunability over the visible light region to realize optoelectronic devices based on the polarization phenomenon. In this regard, OIHPs have emerged as promising candidates for nonlinear optic devices because of their facile color tunability through halide composition engineering, [11] quantum size effects, [12] small effective mass, [13] long spin lifetime exceeding 1 ns, diffusion lengths ≈85 nm, and high electron/hole mobility. [14] A recent study demonstrated that OIHPs exhibit strong spin-orbit coupling of the electronic states, [15] spin-dependent optical selection rules, and large Rashba splitting, [16] suggesting that the OIHPs might exhibit exceptional spin polarization properties. [17] Despite the exceptional spin polarization properties, OIHP materials cannot be utilized in chiral photonics owing to their centrosymmetric crystal structure. However, the flexible crystal Organic-inorganic hybrid halide perovskites (OIHPs) are commonly used as prototypical materials for various applications, including photovoltaics, photodetectors, and light-emitting devices. Since the chiroptical properties of OIHPs are deciphered in 2017, chiral OIHPs have been rediscovered as new hybrid systems comprising chiral organic molecules and achiral inorganic octahedral layers. Owing to their exceptional optoelectrical properties and structural flexibility, chiral OIHPs have received a considerable amount of attention...

Scaling large-area solar cells is in high demand for the commercialization of perovskite solar cells (PSCs) with a high power-conversion efficiency (PCE).However, few roll-to-roll-compatible deposition methods for the formation of highly oriented uniform perovskite films are reported. Herein, a facile cold antisolvent bathing approach compatible with large-area fabrication is introduced. The wet precursor films are submerged in a cold antisolvent bath at 0 °C, and the retarded nucleation and growth kinetics allow highly oriented perovskite to be grown along the [110] and [220] directions, perpendicular to the substrate. The high degree of the preferred crystal orientation benefits the effective charge extraction and reduces the amount of inter-and intra-grain defects inside the perovskite films, improving the PCE from 16.48% (ambientbathed solar cell) to 18.50% (cold-bathed counterpart). The cold antisolvent bathing method is employed for the fabrication of large-area (8 × 10 cm 2 ) PSCs with uniform photovoltaic device parameters, thereby verifying the scale-up capability of the method.

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All‐inorganic cesium lead triiodide (CsPbI3) perovskite is considered a promising solution‐processable semiconductor for highly stable optoelectronic and photovoltaic applications. However, despite its excellent optoelectronic properties, the phase instability of CsPbI3 poses a critical hurdle for practical application. In this study, a novel stain‐mediated phase stabilization strategy is demonstrated to significantly enhance the phase stability of cubic α‐phase CsPbI3. Careful control of the degree of spatial confinement induced by anodized aluminum oxide (AAO) templates with varying pore sizes leads to effective manipulation of the phase stability of α‐CsPbI3. The Williamson–Hall method in conjunction with density functional theory calculations clearly confirms that the strain imposed on the perovskite lattice when confined in vertically aligned nanopores can alter the formation energy of the system, stabilizing α‐CsPbI3 at room temperature. Finally, the CsPbI3 grown inside nanoporous AAO templates exhibits exceptional phase stability over three months under ambient conditions, in which the resulting light‐emitting diode reveals a natural red color emission with very narrow bandwidth (full width at half maximum of 33 nm) at 702 nm. The universally applicable template‐based stabilization strategy can give in‐depth insights on the strain‐mediated phase transition mechanism in all‐inorganic perovskites.

Chiral perovskites are being extensively studied as a promising candidate for spintronic- and polarization-based optoelectronic devices due to their interesting spin-polarization properties. However, the origin of chiroptical activity in chiral perovskites is still unknown, as the chirality transfer mechanism has been rarely explored. Here, through the nano-confined growth of chiral perovskites (MBA2PbI4(1-x)Br4x), we verified that the asymmetric hydrogen-bonding interaction between chiral molecular spacers and the inorganic framework plays a key role in promoting the chiroptical activity of chiral perovskites. Based on this understanding, we observed remarkable asymmetry behavior (absorption dissymmetry of 2.0 × 10−3 and anisotropy factor of photoluminescence of 6.4 × 10−2 for left- and right-handed circularly polarized light) in nanoconfined chiral perovskites even at room temperature. Our findings suggest that electronic interactions between building blocks should be considered when interpreting the chirality transfer phenomena and designing hybrid materials for future spintronic and polarization-based devices.

The crystallographic orientation and phase distribution of two-dimensional Ruddlesden−Popper perovskites (2D-RPPs) should be carefully controlled to obtain high-performance 2D-RPP-based optoelectronic devices. However, these characteristics are still unclear. Herein, we systematically examine the formation mechanism of highly oriented multiphase 2D-RPPs. We argue that the 3D-like perovskites containing small organic cations nucleate first with out-of-plane (111) preferential orientation, followed by the further growth of twodimensional perovskites incorporating bulky organic cations owing to the difference in the solubility between small and bulky cations. This spatial segregation of organic cations across the film depth induces the formation of multiple perovskite phases, which produces n-value-graded 2D-RPP films with continually upshifted band energy alignment. Highly oriented multiphase 2D-RPP films with isobutylammonium (isoBA 2 (Cs 0.02 MA 0.64 FA 0.34 ) 4 Pb 5 I 16 ) were successfully employed as a photoabsorbers for perovskite solar cells (PSCs), exhibiting remarkable efficiency of over 16% and significantly enhanced environmental stability compared with their three-dimensional counterparts.O rganic−inorganic hybrid perovskite materials have shown useful optoelectronic properties for application in various devices, including photodetectors, light-emitting diodes, and solar cells. 1−8 Despite their tremendous potential, the intrinsic instability of organic− inorganic hybrid perovskites against moisture, heat, and light limits their commercialization. 9,10 Recently, two-dimensional Ruddlesden−Popper perovskites (2D-RPPs) have been recognized as a new class of materials that enable high performance and long-term stability. Furthermore, 2D-RPPs have a more widely tunable optoelectronic properties, which originate from their structural versatility and quantum confinement effect, and thus, offer a broader application range than their three-dimensional (3D) counterparts. 11−14 The crystal structure of 2D-RPPs is derived from typical 3D perovskite materials with an ABX 3 composition, where A is an univalent organic cation and B is a divalent metal cation, which are octahedrally coordinated with halide ions X. With the introduction of bulky alkylammonium spacer cations, the chemical composition of 2D-RPPs is expressed as A′ 2 A n−1 B n X 3n+1 (n = 1, 2, 3, ..., ∞), where n is the number of inorganic octahedra layers, which are sandwiched between spacer cations A′ to form unit building blocks. 15 The building