Organic cocrystals possess valuable properties owing to the synergistic effect of the individual components. However, the growth of molecular cocrystals is still in its primary stage. Here we develop a microspacing in-air sublimation method to grow organic cocrystals, and furthermore to realize morphology control on them, which is essential for structure–property relations. A series of polycyclic aromatic hydrocarbon (PAH)‒1,2,4,5-tetracyanobenzene (TCNB) complexes cocrystals are grown directly on the substrate, with the morphology tunable from 1D needle-like to 2D plate-like on demand. Spatially resolved photoluminescence spectra analyses on different cocrystals display morphology dependent and anisotropic optical waveguiding properties. In situ observation and energy calculations of the crystallization processes reveal the formation mechanism being from a competition between growth kinetics-defined crystal habit and the thermodynamics driving force. This growth technique may serve the future demand for tunable morphology organic cocrystals in different functional applications.

Organic single crystals manifest the intrinsic physical properties of materials. However, traditional growth of organic single crystals is limited by low solubility from solutions or complexity from physical vapor deposition. Here we report a new method to grow organic single crystals by microspacing in-air sublimation, which avoids costly vacuum system and time-consuming procedures and is practical for a wide range of organic crystals. In situ crystal growth observation revealed an unprecedented vapor-to-melt-to-crystal mechanism, resulting from the micrometer scale spacing distance between the source and the growth position. FET devices based on the rubrene crystals directly grown on Si/SiO2 substrate exhibited higher mobility than the best record using SiO2 as the gate dielectric. This effective organic crystal growth technique can be affordable and handled for almost every lab, which may be beneficial for future research and application of organic crystals.

The emergence of organic–inorganic halide perovskites has reformed the research status of optoelectronics to a great extent. The bulk single crystals of halide perovskite, which in theory reflect the intrinsic physical properties of the material, are however hard to integrate into functional devices. Just as in the case that silicon wafers have revolutionized modern industries including electronics and solar cells, the availability of perovskite crystal wafers may pave the way to functional devices. Here we designed a new settled temperature and controlled antisolvent diffusion system to precisely control all key factors that affect the supersaturation metastable zone during the crystal growth process, to grow MAPbBr3 single crystals more than 50 mm in size. Second, we fabricated MAPbBr3 single crystal wafers with different orientations, specifically, the (100), (010), (001), (110), and (111) wafers, with high crystalline quality (half-peak width of rocking curve of 60–100 arc sec). Some key parameters were measured and compared on the wafers, where the results hint that anisotropy of carrier transport may exist for this pseudocubic structure. We hope the availability of oriented single-crystal wafers can provide more scientists the materials and devices to clarify the debatable physicochemical properties and to integrate the wafers as active layers or substrates in optoelectronic devices.

Mixed halide coordination has been widely used to finely tune the properties of inorganic and inorganic− organic hybrid compounds, especially for emerging perovskites materials. Despite the increasing number of reports on preparation methods and the affected functionalities, the peculiar and precise role of the doping halogens in structural regulation of the crystals and the resulting variations on the basic properties remain to be addressed. Here, to shed light into the "black box", a new series of [NH 2 (CH 2 CH 3 ) 2 ] 3 Bi(Cl 1−x Br x ) 6 (x = 0, 0.135, 0.255, 0.385, 0.847, and 1) single crystals were grown from the mixed halide solvents by the temperature lowering method. The correlation between the inclusion amounts of Br in the final crystals with the halide concentrations in the precursors is discussed from different perspectives. The two kinds of halogens share the same position in the mixed halide system, with every crystallographically independent halide site possessing different halogen occupancies. The mixed halide coordination exhibits a regulated effect on the distortion of the anion octahedra. Optical absorption, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and the second harmonic generation (SHG) measurements have confirmed that, with increased Br inclusion, [NH 2 (CH 2 CH 3 ) 2 ] 3 Bi(Cl 1−x Br x ) 6 crystals exhibit a regulated effect on their bandgaps, thermal stabilities, and SHG capacities.

It has been proved that bulk single crystals of a halide perovskite behave much better than its polycrystalline counterparts in multiple application scenarios. Thus, the growth of large-sized and high-quality single crystals is significant to guarantee their ultimate device performances. Here, based on our recently invented settled temperature and controlled antisolvent diffusion system, improvements achieved in this work include the following: (1) We modified the growth system to optimize the control over both mass and heat transport to alleviate defect formation. State-of-the-art-quality MAPbBr3 crystals were grown, and from the bulk crystals, differently oriented crystalline wafers were fabricated with the full width at half-maximum of X-ray rocking curves of 40–86 arcsec. (2) The optical band gaps revealed no anisotropy on differently oriented wafers, whereas the refractive index and extinction coefficient exhibited obvious anisotropy. (3) Angle-resolved polarized Raman spectra demonstrate distinct in-plane anisotropy on (100) and (110) wafers but not on the (111) wafer. The equilibrium MA+ orientations are deduced to adopt the <111> direction with the antiparallel MA+ orientation between adjacent domains. (4) Radiation detectors fabricated on differently oriented wafers proved photoresponse anisotropy to both visible and X-ray radiation, following a general order of (100) > (110) > (111). Because anisotropy is an inevitable issue for various applications employing crystalline materials, this study, based on the clarification of the debatable intrinsic dipole configuration in the pseudocubic crystal lattice, will provide quantitative information on physicochemical property anisotropy and subsequently facilitate optimization of device performance referring to crystal orientations of halide perovskite crystals.

Single-crystal-to-single-crystal (SCSC) phase transition is an ideal model to study the structural correlation between the polymorphs at the molecular level. In this regard, a transition process with concomitant emission color change is in favor of direct visualization by fluorescence microscope. Here we report an SCSC transition on the luminescent single crystal of large conjugated molecules, which is accompanied by a drastic luminescence color change from red to orange upon heating. The transition process was clearly recorded under both fluorescence and polarized light. Combining with crystallographic analysis, the results indicate that the existence of molecular layers and the oriented motion of the interface between the daughter and the parent phase preserved the integrity of the single crystal, despite of remarkable changes of both conformational and supramolecular structure. Thus, the transition is rationalized to proceed by a nucleation-and-growth mechanism but not a martensitic one. This work on one hand delivers intuitive cognition about the polymorph-dependent optical properties and the mechanism of the phase transition between the polymorphs and, on the other hand, also proved the paramount importance of direct microscopy observation about the actual transition process.

Owing to quantum confinement, low-dimensional hybrid perovskite materials have recently shown a great potential for applications in optoelectronics. Such compounds can exhibit broad-or narrow-band light emission, lowtemperature solution processability, high thermal stability, and relatively high photoluminescence quantum yields (PLQY). However, the search for efficient phosphors with a specific set of characteristics remains difficult because the family of hybrid perovskites consists in an extremely large chemical system (i.e., different halides, metals, and organic molecules), and optical properties are not predictable prior to material synthesis and characterization. Here, is proposed a simple approach to screen a significant amount of new hybrid lead halide perovskites. The synthetic method by fast crystallization at low temperature enables the rapid identification of the materials exhibiting the targeted photoluminescence properties. This approach is tested for the discovery of hybrid lead halide perovskites with efficient white-light emission. Among 100 newly synthesized compounds, 5 exhibit intense white emission, and the in-depth characterization of a selected candidate shows high color rendering index (CRI) = 78 and a PLQY of 9%, which is equivalent to the record reported for hybrid perovskites. This compound exhibits a new structure type for warm white-light emitting hybrid perovskites with chains of corner-sharing PbX 6 .

Organic single crystals play indispensable roles in high-performance electronic devices because of their completely eliminated or minimized impurities and disorder, wherein ultrathin thickness is a critical prerequisite because charge accumulation in devices occurs within a few molecular monolayers of the semiconductors. The growth of organic crystals through vapor dispels concerns about solubilities and the inclusion of solvents in the final crystals, but achieving an ultrathin thickness for common organic semiconductors is beyond its power. On the basis of our recently invented microspacing in-air sublimation (MAS), the distance between the source and growth position is set to approximate the mean free path of the vaporized molecules. Such a configuration generates a genetic relationship between the morphology of the source materials and that of the grown crystals. By refining the deposition of the source materials using ultrasonic spray, we can obtain ultrathin single crystals with a uniform distribution. We exemplify the strategy through MAS growth of ultrathin DNTT and pentacene single crystals down to five and three molecular monolayers, respectively. Field effect transistors fabricated on the ultrathin crystals exhibited average charge carrier mobilities of 6.08 cm 2 V −1 s −1 for DNTT and 2.39 cm 2 V −1 s −1 for pentacene, and low threshold voltages (∼83% of the devices within 5 V).