Weichuan Zhang

Inorganic–organic hybrid switchable dielectric materials with the coexistence of magnetic anomalies induced by reversible high-temperature phase transition

An inorganic–organic hybrid compound that features a zero-dimensional inorganic structural framework, N-methylpiperidinium tetrabromoferrate(III) (compound 1, [C6H14N][FeBr4]), has been reported as a new switchable dielectric material with the coexistence of weak magnetic anomalies. It is noteworthy that 1 demonstrates remarkable dielectric responses, which can be tuned between two distinct dielectric states and reversibly switched by phase transition at ∼340 K (Tc). Its high-dielectric constants are at least 4 times as large as that of the low-dielectric state. Structural analysis reveals that 1 belongs to the monoclinic crystal system with the space group P21/c at room temperature, but transforms into an orthorhombic system with the space group Cmcm above Tc. The disordering of organic cations affords a driving force for high-temperature phase transition in 1 along with its switchable dielectric activities. Besides, weak magnetic anomalies were also found in 1 at the vicinity of its Tc, which should be reminiscent of another possible physical channel to the phase transition. This finding suggests that 1 might be a potential multifunctional material with the coexistence of switchable dielectric bistability and magnetic responses, which opens up new possibilities to develop molecular functional materials.

Broadband white-light emission with a high color rendering index in a two-dimensional organic–inorganic hybrid perovskite

Two-dimensional (2D) organic–inorganic hybrid layered perovskites have attracted increasing attention as promising candidates in optoelectronics, due to their excellent physical attributes. However, although great efforts have been made, broadband white-light emission with a high color rendering index based on 2D hybrid perovskites still remains rare. Here, we report a broadband white-light emissive 2D organic–inorganic hybrid (110)-oriented perovskite, N-(3-aminopropyl)imidazole tetrachloro-lead (1), in which the 2D corrugated layered inorganic framework is formed by corner-shared highly distorted lead chloride octahedra. Remarkably, the color rendering index of 1 is up to 93, which is superior to that of previously reported broadband white-light emission in 2D organic–inorganic hybrid perovskites. Such a 2D hybrid layered perovskite material with a high color rendering index may provide potential applications in white light-emitting diodes.

[(CH3)3NH]3Bi2I9: A Polar Lead-Free Hybrid Perovskite-Like Material as a Potential Semiconducting Absorber

Perovskite hybrids of lead organometal halides, most notably CH3 NH3 PbI3 , have shown extremely promising applications in the field of optoelectronics, because of their remarkable semiconducting and light-absorbing properties. However, two key issues-the toxicity of lead and the poor ambient instabilities-have restrained their further commercialization. Herein, we have designed a new stable polar lead-free hybrid material by utilizing the strategy of cation substitution, [(CH3 )3 N]3 Bi2 I9 (1), which adopts the 0D inorganic perovskite-like architecture by face-sharing BiI6 octahedra. It is interesting that 1 displays excellent absorbing properties with a narrow optical band gap of ≈2.0u2005eV, and positive temperature-dependent conductivity confirms its semiconducting behaviors. In addition, 1 has good phase stability against decomposition under ambient conditions, much superior to that of CH3 NH3 PbI3 . This work suggests the potential of 1 as a lead-free semiconducting absorber with high phase stability for photoelectric applications.

Lead-Free Hybrid Material with an Exceptional Dielectric Phase Transition Induced by a Chair-to-Boat Conformation Change of the Organic Cation

Hybrid organic-inorganic perovskite materials have demonstrated great potential in the field of photovoltaics and photoelectronics. On the basis of the high degree of structural flexibility and compatibility, diverse molecular functional materials have been assembled by modifying the length of the organic components and/or dimensionality of the inorganic frameworks. In this paper, we present a chiral lead-free organic-inorganic hybrid, (piperidinium)2SbCl5 (1), which follows the one-dimensional inorganic frameworks of the corner-sharing SbCl6 octahedra. Strikingly, 1 displays a dielectric phase transition at Tc = 338 K, changing from the chiral space group of P212121 to polar Pna21 upon heating. Crystal structure analyses reveal that an unusual thermally activated conformation change of the piperidinium cations affords the driving force to the phase transition of 1. That is, organic piperidinium moieties display a chairlike conformation below Tc, which transforms to a boatlike structure above Tc. Such an unprecedented change is strongly coupled to the dielectric transition along with notable steplike anomalies, which suggest that 1 could be used as a potential switchable dielectric material. Besides, the temperature-dependent conductivity and theoretical analysis of its electronic structure disclose the semiconducting behavior of 1. This study paves the pathway to the design of new lead-free semiconducting perovskites with targeted properties for optoelectronic application.

(2-Methylpiperidine)PbI3: an ABX3-type organic–inorganic hybrid chain compound and its semiconducting nanowires with photoconductive properties

Organic–inorganic hybrid semiconducting nanowires have recently been widely regarded as promising candidates for electric and optical applications due to their faster carrier separation and low charge recombination. Here, we reported organic–inorganic hybrid semiconducting nanowires with photoconductive properties based on a one dimensional ABX3-type compound, (2-methylpiperidine)PbI3 (1). In 1, one dimensional infinite double chains are surrounded by protonated organic 2-methylpiperidine cations to form a quantum wire structure, which has been thought to be favorable for carrier transport. Furthermore, the prepared semiconducting nanowires of 1 display obvious photoconductive properties, which have been verified using I–V and time-dependent photoresponse measurements. All the results indicate that such semiconducting nanowires based on low dimensional organic–inorganic hybrid materials have potential photoelectric applications.

Switchable behaviors of quadratic nonlinear optical properties originating from bi-step phase transitions in a molecule-based crystal

Solid-state nonlinear optical (NLO) switches are recently emerging as a new class of promising stimuli-responsive materials for photoelectric application. Herein, we report an organic molecular crystal, N- methylcyclohexylamine picrate (1), which exhibits remarkable switching behaviors of quadratic NLO properties with a large contrast of ∼20 between its NLO-on and NLO-off states. This is almost comparable with the conventional photochromic counterparts, and suggests the great potential of 1 as a quadratic NLO-switching candidate. It is noteworthy that 1 undergoes bi-step structural phase transitions at T1 = 240 K and T2 = 285 K, which are closely associated with its NLO-switching activities. Above T1, disordering of anionic and cationic moieties leads to vanishing of the NLO effect, (i.e. NLO-off state). In contrast, below T1, stepwise frozen ordering of the structural moieties generates strong NLO activities, with the NLO response being ∼0.9 times that of KH2PO4. Such an order–disorder transformation accounts for the high-contrast NLO switching of 1. It is believed that this finding affords an effective strategy for designing new stimuli-responsive materials.

(C6H13N)2BiI5: A One-Dimensional Lead-Free Perovskite-Derivative Photoconductive Light Absorber

Lead-free organic-inorganic hybrid perovskites have recently attracted intense interest as environmentally friendly, low-cost, chemically stable light absorbers. Here, we reported a new one-dimensional (1D) zigzag chainlike light-absorbing hybrid material of (C6H13N)2BiI5, in which the corner-sharing octahedral bismuth halide chains are surrounded by organic cations of tetramethylpiperidinium. This unique zigzag 1D hybrid perovskite-derivative material shows a narrow direct band gap of 2.02 eV and long-lived photoluminescence, which is encouraging for optoelectronic applications. Importantly, it behaves as a typical semiconducting material and displays obvious photoresponse in the visible-light range. This work opens a potential pathway for the further application of 1D lead-free hybrids.

Thermochromism to tune the optical bandgap of a lead-free perovskite-type hybrid semiconductor for efficiently enhancing photocurrent generation

Thermochromic materials have recently attracted great attention due to their controllable and rich physicochemical properties. However, until now, no studies have been reported on thermochromic materials for photovoltaic and optoelectronic applications. Here we report a new lead-free hybrid semiconductor material, (C16H20N2)SbBr5 (1), which adopts the zero-dimensional (0-D) perovskite-type inorganic framework. Strikingly, the thermochromism in 1 leads to a wide tunable bandgap and superior photoelectric properties. Three distinct color-varying stages were first observed, i.e. colorless to yellow (I), yellow to red (II), and red to black brown (III). In particular, the figure-of-merits for thin-film photodetectors based on II-thermochromism were greatly improved, with the dark current lowered to one quarter and light photocurrent enhanced at least 12-fold. The photocurrent on/off switching ratio was thus improved by ∼50 times through thermochromism. As a new conceptual strategy to engineer the optical bandgap and meet specific photoelectric functions, our study paves the way for building high-performance optoelectronic devices based on thermochromic materials.

A lead-free semiconducting hybrid with ultra-high color rendering index white-light emission

Organic–inorganic hybrid perovskites (OIHPs) of lead halides have played a significant role in the field of light-emitting devices and display systems. However, the potential toxicity of lead is considered as one of the main problems for further applications, and it is highly desirable to design the new lead-free OIHPs with outstanding white light emission. Herein, we present a new lead-free single-component hybrid as the potential white light-emitting semiconducting material, [4-methylpiperidinium]2SbCl5 (4-MPSC), which adopts the one-dimensional inorganic chains of corner-sharing SbCl6 octahedra. It is worth noting that 4-MPSC shows the Commission internationale de l’eclairage (CIE) chromaticity coordinates of (0.33, 0.32), which is highly close to the pure white light emission value of (0.33, 0.33). Meanwhile, the white-light emission of 4-MPSC shows an ultra-high color rendering index (CRI) value of 96.29. It is believed that such an ultra-high CRI value will fulfil the requirement for color-critical high-level potential applications. Moreover, 4-MPSC also exhibits semiconducting properties, as verified by the positive temperature-dependent conductivity along with an optical bandgap of 2.93 eV. This work will provide a pathway for further design of new white-light-emitting materials in the lead-free OIHP system.

Above-room-temperature switching of quadratic nonlinear optical properties in a Bi–halide organic–inorganic hybrid

Organic–inorganic hybrid nonlinear optical (NLO) switches have recently attracted intensive attention as potential candidates for optical applications. Herein, by introducing an organic triamine cation, we obtain a lead-free Bi-based organic–inorganic hybrid, (C4H16N3)BiBr6 (1), which behaves as a promising above-room-temperature modulator of quadratic NLO responses. More importantly, 1 possesses a remarkable NLO switching contrast of up to ∼35 and a notable switching repeatability. Additionally, microscopic single-crystal structural analyses reveal that the coordinated distortion of inorganic [BiBr6]3− octahedra and the order–disorder transformation of the flexible organic triamine cations synergistically contribute to its NLO switching behavior. We believe that this work will promote the development of high-performance NLO switching materials based on devisable organic–inorganic metal–halide hybrids.