The bulk photovoltaic effect (BPVE) is a promising optoelectronic phenomenon for generating a steady-state photocurrent without a bias voltage. Nevertheless, the simple and rational design of materials exhibiting the BPVE remains an important topic in the relevant fields. Here, we report the observation of the BPVE in a simple chiral-polar pair of layered perovskite-type lead iodides in the crystal space group of P1 (#1), which were synthesized by assembling R- and S-chiral organic cations, respectively. The sign of the zero-bias photocurrent is altered by the R/S-chirality of the assembled cations, which define the direction of electric polarization derived from the electric dipole moment of each chiral organic cation aligned in a crystal. The strategy of chirality control in a crystal is expected to be useful when searching for BPVE materials.

The circular photogalvanic effect (CPGE) is a novel spin-related optoelectronic phenomenon based on the SOC of noncentrosymmetric systems. [15] Under the CPGE, a steady photocurrent is generated by the irradiation of circularly polarized light (CPL) without an external bias voltage, and the photocurrent direction is reversed by switching the photon helicity. [15,16] The CPGE originates from the asymmetric distribution of photocarriers in a momentum space (k-space) excited by CPL in interband transitions with a spin-flip between the spin-splitting states (Scheme 1). [16] The direction of the zero-bias photocurrent can be controlled based on the helicity of the CPL, as the asymmetric distribution of photocarriers arises from the selection rule of CPL excitation, Δm J = ±1, where m J is the magnetic quantum number of the total angular momentum (Scheme 1). [16] Hence, noncentrosymmetric systems, wherein SOC could induce spin-splitting in electronic states, are promising platforms to generate the CPGE. In fact, the CPGE has been observed in various polar systems, such as group III-V compound semiconductors, [16][17][18][19] the surface of topological insulators, [20][21][22] a bulk Rashba semiconductor, [23] and transition metal dichalcogenides. [24][25][26][27] In these studies, the correlation between polarity and the CPGE was investigated in detail, andThe control of the optoelectronic properties of 2D organic-inorganic hybrid perovskite (2D-OIHP) lead halides is an increasingly prevalent topic. Herein, the observation of the circular photogalvanic effect (CPGE) in new enantiomorphic 2D-OIHP lead iodides is reported, which are synthesized as a first OIHP-related system belonging to a chiral space group by incorporating organic chiral cations into the inorganic layers of lead iodides. The CPGE is an optoelectronic phenomenon associated with the spin-orbit coupling of heavy atoms in noncentrosymmetric systems. Owing to the CPGE, lighthelicity-dependent steady photocurrents are generated without an external bias voltage under the irradiation of circularly polarized light. Furthermore, the sign reversal of the CPGE photocurrent depending on the chirality of the designed 2D-OIHP lead iodides is observed. This result indicates formation of the theoretically predicted radial spin-polarized texture in k-space of chiral systems owing to spin-momentum locking. Hence, chiral 2D-OIHP lead halides can be a promising platform for engineering opto-spintronic functionalities.

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Two‐dimensional organic–inorganic hybrid perovskites (2D‐OIHPs) are attracting interest due to their structural tunability and rich functional characteristics, such as ferroelectricity and ferromagnetism. Here, we report the chiral‐polar ferromagnetic 2D‐OIHP copper chlorides with discernable electric polarization in the inorganic layers. In these systems, the magneto‐electric (ME) correlation has been clearly observed by measuring a magneto‐electric directional anisotropy (MEA), in which an optical absorption coefficient changes with reversal of the light propagating direction. We have found that the MEA can be induced by a low magnetic field of about 50 mT, reflecting soft magnetic nature. The present results suggest a new paradigm for designing functional ME multiferroics, which effectively couples magnetic and electric properties.

The bulk photovoltaic effect (BPVE) is a promising optoelectronic phenomenon that produces a steady-state photocurrent in homogeneous bulk materials without the application of an electric field. In principle, the BPVE is allowed to be observed in noncentrosymmetric systems. However, guidelines on the effectiveness of crystal symmetry for the BPVE, such as chirality and polarity, remain unknown because of the lack of systematically controllable materials. For this reason, three types of noncentrosymmetric two-dimensional organic−inorganic hybrid perovskites (2D-OIHPs) of lead iodides with the formula A 2 PbI 4 and chiral ammonium cations (A + ) were used in the experiments. These were classified as (i) achiral−polar systems, (ii) chiral−nonpolar systems, and (iii) chiral−polar systems. All systems showed a strong current enhancement under light irradiation and an electric field. However, only (i) and (iii) systems showed the BPVE. Furthermore, direction reversal of the detected zero-bias photocurrent (I 0 ) was observed when the direction of the electric polarization was changed. The absence of the detected BPVE in the (ii) system can be attributed to the zero net electric polarization (P) of the crystal structure, whereas (i) and (iii) systems possess nonzero P. Based on these observations, the features of the BPVE in 2D-OIHP lead iodides demonstrated in this work could be interpreted using the shift current mechanism.