By dimensional reduction of the 3D motif of Cs2AgBiBr6, a lead‐free 2D hybrid double perovskite, (i‐PA)2CsAgBiBr7 (1, i‐PA=isopentylammonium), was successfully designed. It adopts a quantum‐confined bilayered structure with alternating organic and inorganic sheets. Strikingly, the unique 2D architecture endows it highly anisotropic nature of physical properties, including electric conductivity and optical absorption (the ratio αb/αc=1.9 at 405 nm). Such anisotropy attributes result in the strong polarization‐sensitive responses with large dichroic ratios up to 1.35, being comparable to some 2D inorganic materials. This is the first study on the hybrid double perovskites with strong polarization sensitivity. A crystal device of 1 also exhibits rapid response speed (ca. 200 μs) and excellent stabilities. The family of 2D hybrid double perovskites are promising optoelectronic candidates, and this work paves a new pathway for exploring new green polarization‐sensitive materials.
In terms of strong light-polarization coupling, ferroelectric materials with bulk photovoltaic effects afford a promising avenue for optoelectronic devices. However, due to severe polarization deterioration caused by leakage current of photoexcited carriers, most of ferroelectrics are merely capable of absorbing 8–20% of visible-light spectra. Ferroelectrics with the narrow bandgap (<2.0 eV) are still scarce, hindering their practical applications. Here, we present a lead-iodide hybrid biaxial ferroelectric, (isopentylammonium)2(ethylammonium)2Pb3I10, which shows large spontaneous polarization (~5.2 μC/cm2) and a narrow direct bandgap (~1.80 eV). Particularly, the symmetry breaking of 4/mmmFmm2 species results in its biaxial attributes, which has four equivalent polar directions. Accordingly, exceptional in-plane photovoltaic effects are exploited along the crystallographic [001] and [010] axes directions inside the crystallographic bc-plane. The coupling between ferroelectricity and photovoltaic effects endows great possibility toward self-driven photodetection. This study sheds light on future optoelectronic device applications.
Multiphoton absorption (MPA) has been utilized for important technological applications. High‐order multiphoton harvesting (e.g., five‐photon absorption, 5PA) exhibits unique properties that could benefit biophotonics. Within this field, perovskite oxide ferroelectrics (e.g., BaTiO3) enable low‐order optical nonlinearities of 2PA/3PA processes. However, it is challenging to obtain efficient, high‐order 5PA effects. Herein, for the first time, giant and broadband MPA properties are presented in the 2D hybrid perovskite ferroelectric (IA)2(MA)2Pb3Br10 (1; IA = isoamylammonium and MA = methylammonium), where multiphoton‐excited optical nonlinearities related to different MPA mechanisms over a broadband range of 550–2400 nm are observed. Strikingly, its 5PA absorption cross‐section (σ5) reaches up to 1.2 × 10−132 cm10 s4 photon−4 (at 2400 nm), almost 10 orders larger than some state‐of‐the‐art organic molecules and a record‐high value among all known ferroelectrics. This unprecedented 5PA effect results from the quantum‐confined motif of inorganic trilayer sheets (wells) and organic cations (barriers) in 1. Moreover, its large ferroelectric polarization of 5 µC cm−2 could promote modulation of MPA effects under external electric fields. As far as it is known, this is the first report on giant, broadband high‐order MPA properties in ferroelectrics, which provides potential, novel electric‐ordered materials for next‐generation biophotonic applications.
Polarized-light detection in solar-blind ultraviolet region is indispensable for optoelectronic applications,whereas new 2D candidates targeted at solar-blind UV range remain extremely scarce.2 Dh ybrid perovskite ferroelectrics that combine polarization and semiconducting properties are of increasing interest. Here,u sing the 3D-to-2D dimensional reduction of CH 3 NH 3 PbCl 3 ,wedesigned amultilayered hybrid perovskite ferroelectric,(CH 3 CH 2 NH 3) 2 (CH 3 NH 3) 2 Pb 3 Cl 10 , which shows spontaneous polarization and ah igh Curie temperature (390 K) comparable with that of BaTiO 3 (393 K). The wide band gap (ca. 3.35 eV) and anisotropic absorbance stemming from its intrinsic 2D motif,greatly favor its polarization-sensitive activity in UV region. The device displays excellent polarization-sensitive behavior under 266 nm, along with al arge dichroic ratio (ca. 1.38) and high on/off current ratio (ca. 2.3 10 3).
Antiferroelectric materials, characterized by an antiparallel array of adjacent dipoles, are holding a bright future for solid-state refrigeration based on their electrocaloric (EC) effects. Despite great advances of inorganic oxides and some organic soft polymers, their EC effects are achieved under quite high electric fields that result in too low EC strengths for practical application. Currently, it is a challenge to exploit soft antiferroelectric with strong EC strengths. Here, by the mixed-cation alloying, we present a new perovskite-type soft antiferroelectric, (isopentylammonium)2CsPb2Br7 (1), which incorporates both an organic spacing cation and an inorganic perovskitizer Cs+ moiety. Remarkably, the synergic cooperativity between the reorientation of the organic spacer and atomic displacement of Cs+ cation triggers its multiple ferroelectric–antiferroelectric–paraelectric phase transitions at 321 and 350 K. Their natural polarization vs electric field hysteresis loops are characterized to confirm ferroelectric and antiferroelectric orders of 1, respectively. It is emphasized that, under a low electric field of 13 kV/cm, the antipolar dipole realignment in 1 endows a giant near-room-temperature EC strength (ΔT EC/ΔE) of 15.4 K m MV–1 at antiferroelectric phase. This merit is on par with the record-high value of BaTiO3 (∼16 K m/MV) but far beyond the state-of-the-art soft polymers. The underlying EC mechanism for 1 is ascribed to the extremely low critical field to switch dipoles, involving the reorientation of the organic spacer and the shift of the Cs+ cation. Besides, notable EC entropy change (∼4.1 J K–1 kg–1) and temperature change (∼2 K) reveal potentials of 1 for solid-state refrigeration. As far as we know, this discovery of near-room-temperature EC strengths is unprecedented in the hybrid perovskite family, which sheds light on the exploration of new soft antiferroelectrics toward high-efficiency refrigeration devices.
2D hybrid perovskites demonstrate better performances than 3D counterparts in certain optoelectronic devices, whereas their natural attributes cannot be extracted from microcrystalline films, such as the natural dichroism for polarized light detection. Herein, for the first time, unusual minute‐scale rapid crystallization is developed to grow bulk crystals of 2D hybrid perovskite, (FPEA)2PbI4 (1, FPEA is p‐fluorophenethylammonium), which enables superior carrier transport property (≈64.1 ns) and low trap density (≈1010 cm−3). The rapid growth rate of 27.3 mm3 h−1 is almost two orders of magnitude higher than for other 2D counterparts. Strikingly, its natural quantum‐confined motif results in extraordinary dichroism with optical absorption ratio αc/αa ≈ 2.05, revealing great promises for polarized light detection. Consequently, crystal‐based photodetectors exhibit large photocurrent dichroic ratio Imax/Imin ≈ 2.1, fast response time (400 µs), and high detectivity (1011 Jones) to the polarized light. This is the record‐fast crystallization of highly dichroic 2D hybrid perovskites, which opens a new prospect for their future optoelectronic device applications.
By dimensional reduction of the 3D motif of Cs2AgBiBr6, a lead‐free 2D hybrid double perovskite, (i‐PA)2CsAgBiBr7 (1, i‐PA=isopentylammonium), was successfully designed. It adopts a quantum‐confined bilayered structure with alternating organic and inorganic sheets. Strikingly, the unique 2D architecture endows it highly anisotropic nature of physical properties, including electric conductivity and optical absorption (the ratio αb/αc=1.9 at 405 nm). Such anisotropy attributes result in the strong polarization‐sensitive responses with large dichroic ratios up to 1.35, being comparable to some 2D inorganic materials. This is the first study on the hybrid double perovskites with strong polarization sensitivity. A crystal device of 1 also exhibits rapid response speed (ca. 200 μs) and excellent stabilities. The family of 2D hybrid double perovskites are promising optoelectronic candidates, and this work paves a new pathway for exploring new green polarization‐sensitive materials.
3D perovskite CsPbBr3 has recently taken a blooming position for optoelectronic applications. However, due to the lack of natural anisotropy of optical attributes, it is a great challenge to fulfil polarization‐sensitive photodetection. Here, for the first time, we exploited dimensionality reduction of CsPbBr3 to tailor a 2D‐multilayered hybrid perovskite, (TRA)2CsPb2Br7 (1, in which TRA is (carboxy)cyclohexylmethylammonium), serving as a potential polarized‐light detecting candidate. Its unique quantum‐confined 2D structure results in intrinsic anisotropy of electrical conductivity, optical absorbance, and polarization‐dependent responses. Particularly, it exhibits remarkable dichroism with the photocurrent ratio (Ipc/Ipa) of ≈2.1, being much higher than that of the isotropic CsPbBr3 crystal and reported CH3NH3PbI3 nanowire (≈1.3), which reveals its great potentials for polarization‐sensitive photodetection. Further, crystal‐based detectors of 1 show fascinating responses to the polarized light, including high detectivity (>1010 Jones), fast responding time (≈300 μs), and sizeable on/off current ratios (>104). To our best knowledge, this is the first study on 2D Cs‐based hybrid perovskite exhibiting strong polarization‐sensitivity. The work highlights an effective pathway to explore new polarization sensitive candidates for hybrid perovskites and promotes their future electronic applications.
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