Crystal growth is affected by both crystal growth kinetics and thermodynamics. It is not only restricted by various physical and chemical factors at multi-scale level, such as crystal structure symmetry, valence bond type between constituent elements, crystal defects, etc., but also affected by growth conditions and growth environment at multi-level level^[19,20]. The so-called crystal growth is simply a process of continuous transformation from metastable state to steady state, or a process of continuous formation and growth of crystal nuclei^[21]. The growth morphology of crystals includes geometric morphology and growth size. The macroscopic morphology of crystals is basically determined by the environmental conditions of crystal growth, while the microscopic morphology is limited by the intrinsic characteristics of materials, both of which are equally important^[22]. The principle of minimum free energy in crystal growth thermodynamics is the basic thermodynamic condition to control the morphology of crystal growth, that is, to finally select the phase state with minimum free energy.The increase or decrease of the crystal size will affect the shape change of the crystal. The smaller the crystal size is, the easier it is to obtain a balanced growth environment. With the increase of the crystal size, the growth environment controlling the growth of the crystals will become asymmetric^[22]. The classical morphological kinetic theories of crystal growth include the BFDH (Bravais-Friedel-Donnay-Harker) model, the periodic bond chain (PBCs) theory, and the crystal face attachment energy model^{[23][24,25][24,26]}. From the kinetic point of view, the crystal growth morphology is determined by the anisotropy of the growth rate.

In the BFDH model, the Bravais rule holds that the final morphology of the crystal is determined by the crystal face with the largest face network density, and the larger the face network density is, the more important the crystal face is^[27]. Subsequently, Friedel, Donnay, and Harker improved the rule and further considered the influence of the screw axis and slip plane in the crystal structure on the final morphology^[27,28]. However, this model can only predict the ideal growth morphology of crystals, and does not clarify the reason why the same crystal may grow in different conditions to obtain different growth morphologies. In crystals, there is a periodic repeating arrangement of chain bonds formed by a series of strong bonds connected uninterruptedly, which is called periodic bond chain^[28]. The direction of PBC is characterized by PBC vector, and the possible crystal planes in the crystal can be divided into F plane, S plane and K plane according to different vector orientations. According to the PBC theory, in real crystals, the F plane often appears as a larger crystal plane, the K plane is often missing, and the rest of the crystal planes are S planes with smaller growth. Perfected by Hartman, the method of quantitative calculation of crystal growth rate can be used to predict the theoretical growth habit of crystals. However, the PBC theory is not perfect: first, it does not unify the influence of growth environment and conditions on the growth morphology of crystals, and second, the growth habit of polar crystals cannot be explained. Later, Zhong Weizhuo proposed the growth unit model of anion coordination polyhedron, which studied the internal structure, growth morphology, growth conditions and defects of crystals in a unified way. The growth habit of crystals was predicted by using the hypothesis of the existence of growth units and the hypothesis of structural consistency, which has successfully explained the growth habit of BaTiO₃, α-Al₂O₃, ZnO, ZnS, SiO₂ and other crystals^[28,29][28].

The above is the classical crystal growth kinetics theory. With the development of crystal design growth, the classical theory is not enough to explain the new crystal growth phenomena, and many non-classical crystal growth theories emerge as the times require. For example, in solution crystallization, the evaporation rate of a solvent at a constant temperature is determined by its vapor pressure. The ideal evaporation rate J_evap can be described by the Langmuir equation:

Where p_v is the vapor pressure of the solvent (according to Raoult's law, the vapor pressure of the solution ≈ that of the pure solvent), R is the gas constant, and T is the absolute temperature. It can be seen from equation (1) that the higher the vapor pressure, the higher the evaporation rate. It is well known that the higher the boiling point (B. P.) value, the lower the vapor pressure of the solvent. Therefore, B. P. Has an inverse relationship with the evaporation rate, i.e., B. P. The higher, the lower the evaporation rate.

Accordingly, it can be seen from that equation (2) that by selecte an appropriate B. P. The solvent can adjust the evaporation rate of the dilute solution. The supersaturation of the system can be expressed in terms of the supersaturation S and the relative supersaturation:

Where C is the solution concentration and C * is the equilibrium saturation concentration at a given temperature. From a thermodynamic point of view, the basic driving force for crystallization is the difference （$\Delta\mu$） between the chemical potentials of a solute in solution and in a crystal, e.g. Solution (state 1) and crystal (state 2), which can be expressed as:

The chemical potential µ is defined in terms of the standard potential µ₀ and the activity a:

Therefore, the fundamental dimensionless driving force for crystallization can be expressed as:

Where A * is the activity of the saturated solution and S is the degree of supersaturation. It can be seen from equation (7) that the crystallization driving force is determined by the supersaturation S. In the case of classical homogeneous nucleation, keeping constant temperature and pressure, the total Gibbs free energy change ΔG of the nucleation process can be expressed as:

Where $\gamma$ is the interfacial tension of the crystal in contact with the solution, V is the molar volume of the crystal molecule, and the maximum value of ΔG corresponds to the critical nucleus r_c, which can be maximized by Equation (8) for a spherical nucleus. Let d_ΔG/d_r=0, we get:

The critical size r_c represents the minimum size of a stable nucleus. Nuclei smaller than r_c dissolve and nuclei larger than r_c continue to grow. Combined with formula (8), we obtain:

The value of ΔG_c represents the energy barrier for stable nucleation, and from equation (9), to start stable nucleation, the size of the crystal nucleus should be larger than r_c, which is determined by the supersaturation S. When S is large, r_c is small and ΔG_c is small, and vice versa. The nucleation rate J, the number of nuclei formed per unit volume per unit time, can be expressed by the Arrhenius velocity equation:

It can be seen from equation (11) that for a system with constant temperature and pressure (T and p are fixed), the nucleation rate is determined by the supersaturation ratio S, and once a certain critical supersaturation level is exceeded, J will increase rapidly.

From the above analysis, it can be seen that the control of supersaturation is the key in the process of solution crystallization. Classical crystallization often leads to a high density of molecular steps that trap charge carriers and reduce the mobility of organic semiconductors. In the classical crystallization process, molecules are reflected by the Ehrlich-Schwoebel Barrier (ESB) and cannot cross the molecular layer until the initial molecular layer is full, thus continuing to nucleate and grow in another layer, thus showing the characteristics of three-dimensional growth and producing organic single crystals with high-density molecular steps^[30].

Two-dimensional organic single crystals with atomically flat crystal faces were obtained by two-step crystal nucleation growth in our group^[30]. Different from the traditional crystal crystallization theory, the melting stage is introduced to reduce the influence of the ESB barrier, and the crystal growth mode is changed from three-dimensional growth to two-dimensional layer-by-layer growth, so that a large-area two-dimensional molecular crystal without molecular stages is generated. As shown in fig. 2, a C6-DPA (2,6-Bis (4-hexylphenyl) anthracene) organic semiconductor is used, and the two-step growth method is realized by dropwise adding a solvent twice on a glycerol liquid substrate, wherein a good solvent with a low boiling point is dropwise added for the first time to rapidly volatilize the solvent to form a crystal nucleus, and a good solvent with a low boiling point is dropwise added for the second step to enable the crystal to grow in a fixed region. By comparing the one-step growth method with the two-step growth method, and using solvents with different boiling points to control the two-step reaction, the number of crystals nucleated and grown can also be changed by changing the time of the second drop of solvent, in which the supersaturation (S) is the key factor affecting the nucleation and growth of crystals. It can be seen from fig. 2j that crystallization is not possible in the stable region (unsaturated, S < 1); Spontaneous crystallization in the metastable region (supersaturation, S > 1) is not possible, however, crystal growth occurs if nuclei appear; Spontaneous crystallization may occur in the unstable region (supersaturation, S > > 1). We consider that in the nucleation stage, S must be large enough to cross the energy barrier for stable nucleation; In the crystal growth stage, S should not be as high as in the nucleation stage, because nucleation should end and only crystal growth is allowed (S ≈ 1). Through a two-step crystal growth procedure, a step change in S (Figure 2K) is achieved, thus reconciling this contradictory requirement for S. Field-effect transistors were constructed using the crystals prepared by the two methods, and it was found that the two-step growth method had higher mobility and better device performance. The Marangoni effect is a phenomenon in which the mass changes due to a tension gradient between two liquid interfaces with different surface tensions^[31]. Fu Yu et al., School of Science, Northeastern University, used the Marangoni effect to make the tension gradient between two liquid interfaces with different surface tensions to move the mass, and finally grew a cm-scale large Zn-MOF (zinc acetate and 1,1 '-biphenyl-2,2' -dicarboxylic acid) single crystal^[32].

Traditional organic molecular crystal growth methods include melt method, solution method and gas phase method. Melt methods such as Czochralski method, Bridgman method, flame melting method, zone melting method, cold crucible shell melting method; Solution methods such as low temperature solution method, high temperature solution method, liquid phase electrodeposition method, hydrothermal method and solvothermal method; Vapor phase methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), etc. Table 1 is a summary of current crystal growth techniques. Through research and development, it is found that large-size organic molecular crystals can be grown by changing the temperature, growth rate, concentration, and introducing impurities on the basis of the classical growth mode, and by improving or controlling the change of one or more quantities. Here, we will focus on large-scale organic molecular crystals, focusing on how organic molecular crystals grow, and also involve large-scale organic molecular crystal films.

Single crystals are the cornerstone of the development of modern microelectronics, solid-state electronics, and optoelectronics^[53]. By using the unique properties of organic single crystals, key performance breakthroughs have been made in optoelectronic devices such as organic field effect transistors, optical waveguides and lasers. However, previous studies were mainly based on organic bulk crystals or small-sized organic micro/nanocrystals. The large-size single crystal can meet the requirements of large-area and low-cost production, realize the integration and functionalization of optoelectronic devices, and break through the application limitation of small-size crystals. Large-size organic single crystals are often more difficult to grow than large-size inorganic single crystals due to various growth conditions. Compared with inorganic crystal growth, organic molecules have relatively weak Van der Waals forces and poor thermal stability, so it is very difficult to require molecular growth units with large size^[52]. Therefore, it is still a big challenge to grow large size and high quality organic single crystals.

Organic scintillators can be used in room-temperature solid-state maser, however the large number of twins and other internal defects in the crystal may hinder the conversion of pump energy to maser radiation. Tao Xutang et al., Department of Chemistry, Shandong University, used the melt growth technique to make the growth conditions more suitable for organic materials by changing the relative motion mode between the ampoule and the oven in the growth device^[52]. At the same time, the growth atmosphere can be adjusted to change the physical response of the crystal to stimuli, such as producing a longer excited state lifetime to meet the high conversion efficiency of the paramagnetic maser. They grew single crystals with good quality, good integrity and uniform doping, and the size reached φ18 mm × 80 mm (Fig. 8), and the crystals were proved to be of good quality by Laue back reflection and high-resolution X-ray diffraction measurements. The effect of optical properties and doping concentration shows that the absorption and luminescence ability of pentacene doped in p-terphenyl crystal is greatly improved compared with pentacene dissolved in isotropic liquid.

Our research group prepared centimeter-scale dark blue needle-like F_xMePcs（Me=Cu,Zn） crystals (X = 0, 4, 8, 16) (Fig. 9) by vapor transport method, and then studied the structure-property relationship of these materials.It is found that with the increase of fluorination, the single crystal field effect device changes from p-type to n-type, which realizes the adjustment of organic semiconductor from p-type to n-type, and proves the relationship between molecular symmetry and device performance^[54].

Nonlinear Optics (NLO) organic molecular crystals tend to have large crystal sizes, and Verma et al., Raja Ramanla Center for Advanced Technology, India, have grown urea-doped L-cysteine hydrochloride hydrate NLO organic molecular crystals with a size of 22×20×5 mm³（ Fig. 10 a), and they used time-lapse photography to continuously monitor the growth^[55]. Teng Bing et al., School of Physical Sciences, Qingdao University, grew a high-quality organic nonlinear optical crystal 2- (4hydroxystyryl) -3-methylbenzothiazolium 4-methylbenzenesulfonate (OHB-T) with a size of 10×4×4 mm³ from a saturated methanol solution at 45 ° C under a controlled cooling rate (Fig. 10B), with a transmittance of 75%^[56]. The results of dielectric properties show that the OHB-T crystal has a low dielectric constant （ε_r=4）, which can be used in electro-optic modulators. The OHB-T crystal has a strong green radiation emission at 550 nm, which can be used in light-emitting diodes. The results show that OHB-T crystal is a potential NLO material.

Wafer-scale growth of single-crystal thin films is essential for the fabrication of high-performance electronic and optical devices, but remains challenging from a scientific and industrial point of view^[57]. Crystalline thin films are often used to construct optoelectronic devices, such as field effect transistors, photodetectors, etc. Therefore, the compounds for growing crystalline thin films are often organic semiconductor materials, including small molecular organics, large molecular organics, polymers, etc. The use of different semiconductor materials has a great impact on the performance of the device. At the same time, the quality of the crystal film growth and the device structure have an impact on the mobility, photocurrent switching ratio, threshold voltage, responsivity and other parameters. Large-scale single-crystal thin films are essential for the fabrication of high-performance electronic or optical devices with good reproducibility, and the study of the growth of large-area crystalline thin films not only lays the foundation for large-area applications of optoelectronic devices, but also helps to study the structure-morphology-performance correlation of thin-film transistor devices^[57]. Because the crystallization of organic crystal films usually nucleates randomly, it is a great challenge to grow large organic single crystal films with good arrangement and directional growth. Jie Jiansheng, Institute of Functional Nano and Soft Matter, Soochow University, proposed the concept of "directional filter funnel" to grow large area C8-BTBT single crystal films.By rationally designing the solvent wetting/dewetting mode on the substrate, this method can produce seed crystals with the same crystal orientation, and then maintain the epitaxial growth of these crystals, resulting in the formation of large-area organic crystal films^[53]. This unique crystal growth concept not only increases the average mobility of organic thin films by 4.5 times, but also improves the uniformity of their electrical properties, with a mobility variation coefficient as low as 9.8%, which is superior to that of organic field-effect transistor devices of the same period (Fig. 12b). Chan et al., Department of Mechanical Engineering, University of Hong Kong, selected C_n-DNTT with different alkyl chain lengths (n = 6, 8, 10, and 12) to deposit 1.5 inch × 1.5 inch C_n-DNTT monolayer crystals by solution shear method, as shown in Figure 12B^[58]. The single crystal area of all C_n-DNTT is larger than 1 mm²（ shown as uniform color under cross polarization microscope (CPOM) in Fig. 13C – f), the electrical properties can be tested within one single crystal area to avoid grain boundary effect and structural inhomogeneity.

Recently, eutectic engineering has emerged as an effective approach to build functional materials. The preparation technique of organic cocrystals can avoid the harsh experimental conditions (i.e., high temperature and pressure) commonly used in chemical bond synthesis^[59,60]. In addition, the intermolecular bonds between the constituent molecules will compete and cooperate to form an ordered crystal packing structure, which is conducive to different molecular recognition, cocrystal formation, and functional exploration^[61]. The cocrystal with highly ordered D-a arrangement can be easily prepared by a low-cost and simple solution method using the non-covalent interaction between the donor molecule and the acceptor molecule. The cocrystal can not only maintain its individual molecular properties, but also exhibit new properties resulting from intermolecular cooperative effects, such as metallic conductivity, ambipolar charge transport, room temperature ferroelectricity, stimulus response, white light emission, optical waveguide, and room temperature phosphorescence.

Hu Wenping of the Institute of Chemistry of the Chinese Academy of Sciences used Spe-F₄DIB eutectic and Npe-F₄DIB eutectic to prove that the optical properties of organic materials can be reasonably controlled by eutectic^[62,63]. Current eutectic optoelectronic devices are typically based on micro/nano-sized crystals. They are usually grown on substrates with random orientation and disordered distribution, which hinders the further application of eutectics in large-area electronic devices. Our group designed and fabricated a large-area (ZnTPP-C₆₀, ZCC) 2D co-crystal with strong NIR absorption self-assembled by zinc tetraphenylporphyrin (donor) and C₆₀（ acceptor), which absorbs at a wavelength up to 1080 nm and has a responsivity of 2424 mA·W^-1 for NIR light with a response time of only 0.6 s^[64]. ZCCs of two morphologies (one-dimensional nanowire and two-dimensional nanosheet) were first prepared, revealing the controlled growth of eutectic morphologies. Then, 1,2-dichlorobenzene was used as a solvent to prepare a high-quality ZCC eutectic film by a simple and low-cost solution epitaxy method (Fig. 13A). From the optical microscope and polarizing microscope, it can be seen that the crystal film is a uniform monocrystalline film without grain boundaries (Fig. 13b, C, d). The atomic force microscopy (AFM) image (Figure 13E) shows that the root-mean-square (RMS) roughness of the ZCC eutectic film is small, 0.591 nm, demonstrating the high quality and crystallinity of the ZCC film. The TEM image also shows the uniform morphology of the ZCC film (Figure 13 f), and the SAED test results correspond to the single crystal XRD data of the ZCC. Transient absorption spectroscopy and device structure optimization are further used to prove that the excellent performance of the device is due to the generation of long-lived free carriers, which provides a reference for further control of large area electronic devices and eutectic active layers in applications.

Liu Yang et al., State Key Laboratory of Crystal Materials, Shandong University, grew a centimeter-sized long afterglow luminescence doped organic molecular crystal by modified Bridgman method (melt growth method), in which p-terphenyl was used as the host molecule in the form of doping.BP/BBP/DBBP doped into the host molecule in a certain proportion showed enhanced Long Persistent Luminescence (LPL), and the lifetime was nearly three orders of magnitude longer than that of the pure guest molecule^[34]. Moreover, the wavelength, lifetime, and quantum yield of LPL can be tuned by different host-guest combinations and doping concentrations. Theoretical optimization shows that the guest molecule is substitutional rather than interstitially embedded in the host lattice. The results show that melt growth is an effective method to establish and finely control the host-guest long and persistent luminescence system. The phosphorescence of pure organic materials is very rare. Kim et al., Department of Materials Science and Engineering, University of Michigan, realized the phosphorescence of pure organic materials through three factors: aromatic carbonyl, heavy atom effect and halogen bonding into the crystal, and the grown Br6a, Br6a/Br6, BrC6a/BrC6, Br6a/Br6, Np6a/Np6 and BrS6a/Br S6 crystals showed centimeter-scale size^[65]. The principle is that the aromatic carbonyl group exhibits a certain degree of spin-orbit coupling on the carbonyl oxygen, allowing the generation of an intrinsic triplet state through intersystem crossing, the heavy atom effect promotes the singlet to triplet state conversion, and the halogen bonding brings the aromatic carbonyl group and the heavy atom effect together in an unprecedented synergistic effect. The heavy atom effect is finally brought into play where the triplet state is generated, amplifying the triplet generation and exciting the emission of the triplet state, phosphorescence. Jin Weijun et al., School of Chemistry, Beijing Normal University, successfully prepared three large-size organic phosphorescent co-crystals formed by 1,4-diiodotetrafluorobenzene (1,4-DITFB) and bent 3-ring-N-heterocyclic hydrocarbons (3-R-NHHs) (phenanthridine (PHN), benzo [f] quinoline (BfQ), benzo [H] quinoline (BhQ)) based on halogen bonds and other interactions^[66].

Nonlinear optical crystals have nonlinear optical effects, which can change the wavelength of laser, broaden the wavelength of laser, and make laser more effective applications. The most important purpose of nonlinear optical crystals is to double the frequency of laser and produce second harmonic. Organic nonlinear optical crystals are composed of conjugated molecules with charge transfer characteristics, so that their second-order polarizability is 1 to 2 orders of magnitude higher than that of ordinary inorganic groups. Especially in the terahertz band (electromagnetic waves between microwave and infrared bands with frequencies in the range of 0. 1 ~ 10 THz), compared with inorganic materials, organic 4- (4-dimethylaminostyryl) methylpyridinium p-toluenesulfonate crystals can generate terahertz pulses in the range of 7 ~ 20 THz, and can obtain the largest range of continuous bandwidth output in the whole terahertz band^[67]. Organic nonlinear optical crystals are more advantageous than inorganic nonlinear optical materials in high nonlinearity and fast response of electro-optic effect, and may play an important role in second harmonic generation (SHG), frequency mixing, electro-optic modulation and optical parametric oscillation^[68].

Kwon et al., Department of Molecular Science and Technology, Asia University, Korea, have grown two kinds of electro-optic crystals in confined geometry, which have good optical quality, large area and sub-millimeter thickness, and are the best crystal properties for efficient terahertz wave generation^[69]. It was found that HMQ (2- (4-hydroxy-3-methoxystyryl) -1-methylquinolinium) -TMS (2,4,6-trimethylbenzenesulfonate) crystals grown in confined geometry exhibited terahertz generation characteristics comparable to those of very flat HMQ-TMS crystals prepared by the cutting method.

A variety of imaging applications, from security inspection to medical diagnostics (Fig. 15), rely on the design and fabrication of X-ray imaging scintillators with high spatial resolution at low radiation dose rates^[70]. X-ray imaging reflects the mass-thickness contrast of the measured object. The higher the atomic number Z, the thicker and denser the sample, and the darker the image^[71]. Current X-ray imagers are mainly based on expensive inorganic materials, which process heavy metals through high-temperature solid processes (up to 1700 ℃) with high toxicity, high temperature and complexity, so it is urgent to find new materials with low growth temperature, low cost, high sensitivity, high chemical stability and environmental stability, and organic materials are meeting the above needs^[71,72]. First of all, the size of micro-nanocrystals can not meet the requirements of X-ray imaging; Secondly, the production of large-sized crystals requires the purity of raw materials, the growth of crystals with less impurities, and the growth of large-sized organic molecular crystals with small defects and excellent performance, so it is necessary to grow large-sized crystals to meet the needs of device preparation, and then further use them for X-ray imaging through cutting and other processes.

X-ray imaging plays an important role in the nondestructive detection of the internal structure of an object. Inorganic scintillators have been widely used in X-ray imaging, but these inorganic scintillators are usually grown by high temperature growth methods to form single crystal or polycrystalline ceramics, which makes them unsuitable for the manufacture of flexible X-ray detectors. New scintillators with low growth temperature, low cost, high sensitivity, good chemical stability and environmental stability can be obtained by using organic semiconductors. Hu Wenping, Department of Chemistry, College of Science, Tianjin University, has shown that organic semiconductors can be used for X-ray imaging with low cost, high sensitivity and low dose.In this study, a large 9,10-diphenylanthracene (9,10-DPA) single crystal with a length of 4. 5 cm was grown by low temperature solution growth technique, and the single crystal showed strong X-ray radioluminescence, with ultra-high photon conversion efficiency, ultra-fast response and high sensitivity^[71]. At the same time, the crystal shows high cycle performance and environmental stability under X-ray irradiation. The resolution of the 9,10-DPA crystal used for X-ray imaging was confirmed using a linear mask consisting of lines with widths ranging from 50 to 300 µm, and a line with a half-peak width of 50 µm could be clearly imaged under X-ray synchrotron radiation with a photon energy of 18 keV (Fig. 16 a, B), after which they performed clear imaging of the sign of Tianjin University (Fig. 16 C, d), demonstrating the high resolution of organic single crystals. They constructed an X-ray imaging device as shown in Figure 16 e, and the test sample can be placed between the X-ray synchrotron radiation source and the organic crystal. When they put them into the circuit board, they can get the X-ray image shown in Figure 16f. The X-ray transmittance through the circuit board is determined by the material of the circuit board and the thickness of different metals. Therefore, there is a very obvious brightness difference from No.1 to No.4. In addition, they used dried shrimp as a representative biological sample for X-ray imaging, and found that in addition to the outline of the shrimp, the internal details of the shrimp could also be clearly imaged (Fig. 16g). In order to confirm the imaging mechanism of the organic crystal, scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS) maps (Fig. 16 h-j) were also performed, and the above results confirmed the applicability of their organic crystal in biological X-ray imaging.

Fast neutron detection can use the "organic characteristics" of organic semiconductors to make neutrons scatter elastically with hydrogen atoms, produce recoil protons, and make the detector produce electrical signals.At the same time, the low atomic number of organic materials is close to the atomic number of human tissues, which makes organic materials superior to inorganic semiconductors in medical detection and treatment, and compact detectors are prepared to accurately detect the target position^[73].

In order to solve the interference of γ-rays, it is necessary to identify fast neutrons and γ-rays. Hu Wenping et al., Department of Chemistry, College of Science, Tianjin University, used the liquid surface assisted growth strategy (liquid-liquid method/gas-liquid method) to obtain high-quality centimeter-sized TPE single crystals and typical DPA single crystals used in parallel experiments^[74]. By comparing the detection ability of TPE and DPA for fast neutrons and γ-rays, they found that the fluorescence lifetime of TPE is only 1.6 ns, while the fluorescence lifetime of DPA is 8 ns, which means that the irradiation response of TPE is faster, and TPE is not sensitive to high-energy photons. As shown in Fig. 17A, B, under the condition of the same radioisotope, the DPA exhibits a strong pulse, meaning that the DPA cannot achieve pulse height discrimination for fast neutrons, because the TPE exhibits a feature insensitive to γ-rays.The pulse intensity is obviously low, so that the neutron-induced delayed fluorescence can be identified by the PSD, and the neutron-induced strong prompt fluorescence can be identified by the PHD, the sensitivity value is 2.4, and the neutron proportion is 35.5%. This work sheds new light on the design and selection of neutron discriminating materials.

Compared with inorganic molecular ferroelectric materials, molecular ferroelectric materials have the advantages of light weight, good mechanical flexibility, easy preparation, good biocompatibility and the like, and can carry out mutual conversion between mechanical energy and electric energy.Molecular ferroelectric materials with large piezoelectric response face challenges in growing large crystals, which is a key limiting factor in measuring electromechanical coupling factor k₃₃^[75,76]. The large size organic-inorganic hybrid [Me3NCH2Cl]CdCl3（TMCM-CdCl₃） molecular ferroelectric crystal grown by Xiong Rengen et al. In the College of Chemistry and Chemical Engineering of Southeast University has large k₃₃（ (conversion efficiency between electric energy and mechanical energy) and d₃₃（ (ratio of strain to applied field strength).Piezoelectric properties of the TMCM-CdCl₃ were characterized using quasi-static method. The resonant behavior was measured for longitudinal extensional, transverse extensional and thickness-shear modes of vibration.The corresponding piezoelectric constants d₃₃, d₃₁, and d₁₅ were determined to be 383, 176, and 667 pC/N, respectively,The electromechanical coupling factors k₃₃, k₃₁, and k₁₅ are 0.483, 0.624, and 0.423, respectively, which are much higher than those of other molecular ferroelectrics and comparable to U BaTiO₃（BTO 0.5)^[77]. In addition to the high-voltage electrical properties, TMCM-CdCl₃ also exhibits low elastic modulus and hardness of 13.03 and 0.60 GPa, which are an order of magnitude lower than those of BTO. These properties make TMCM-CdCl₃ an excellent choice for flexible and wearable piezoelectric device applications.

Tayi et al., Department of Materials Science and Engineering, Northwestern University, USA, used phthalic diimine as molecular acceptor and derivatives of naphthalene, pyrene and tetrathiafulvalene as molecular donors to grow large crystals with a length of about 2 cm.Moreover, the crystal shows the characteristic of room temperature ferroelectricity, which breaks the cognition that the donor-acceptor mixed stacking material cannot show ferroelectric Tc above room temperature, and provides a new idea for designing and synthesizing organic room temperature ferroelectric materials in the future^[78].

The invention of the transistor has made the field of crystal growth more application-oriented^[12]. Field-effect transistors made of organic single crystals are ideal materials for studying the charge transport properties of organic semiconductor materials^[79]. The main factor affecting the performance of organic thin film transistors (OTFTs) is the carrier mobility, which can be improved by improving the grain size and crystalline quality of organic thin films, so the growth of large two-dimensional crystal structures is beneficial to improve the device performance^[80]. Because the crystallization of organic single crystal thin films (OSCF) usually nucleates randomly, different crystal orientations may lead to different mobility of devices, which affects the performance of devices and hinders practical applications. It is a great challenge to grow large organic single crystal thin films with good alignment and directional growth. Hu Wenping of the Institute of Chemistry of the Chinese Academy of Sciences used a Two-step solution epitaxy growth method to self-assemble micron-sized two-dimensional crystals of organic semiconductors-2DCOS on water, and then epitaxially grow 2DCOS with a thickness of several molecular layers^[81]. Nine organic semiconductors with different molecular structures are selected to prove the universality of this method. Among them, the size of 2D COs of polyethylene is close to 1 cm. They constructed 2D COSs into organic field-effect transistors and found that they had excellent electrical properties (Figure 18). This method provides a convenient way for large-scale, high-quality, structurally and functionally novel 2DCOS devices to be applied in the field of flexible optoelectronics.

Takeya et al. Have successfully demonstrated the selective deposition of monolayer (1 L), bilayer (2 L), and trilayer (3 L) molecular single crystals with wafer-scale coverage by optimizing the meniscus-driven crystal growth technique at the Materials Innovation Research Center and Department of Advanced Materials Science, University of Tokyo, Japan^[82]. The wafer-scale layered organic monocrystalline film obtained by them, which consists of only a few molecular layers, has a sufficiently high carrier mobility 13 cm²·V⁻¹·s⁻¹ and a very low contact resistance of 46.9 Ohm · cm. The optimization of this technique enlarges the area coverage of the layer-controlled ultrathin single crystal film, and the one-step deposition method they invented is applicable to any substrate. These excellent 2D molecular wafers support high frequency operation with a channel length of 3 mm, responding at 20 MHz with an applied voltage of − 10 V. In addition, the diode-connected 2L-OFET shows a rectification capability of up to 29 MHz, which is higher than the frequency commonly used in RF-ID tag wireless communication. As a result, they believe that this technology for preparing ultra-thin single crystals will help to realize high-speed organic electronic devices and open the way for new 2D materials to realize large-scale integrated circuit products on thin film-based devices.

In the application of optical, electronic and optoelectronic devices, the assembly of high-performance optoelectronic devices has a high demand for large-size semiconductor crystal materials. For example, the photoelectric conversion efficiency of commercial monocrystalline silicon in the photovoltaic and optoelectronic fields is much higher than that of polycrystalline and amorphous materials. Recently, emerging organic-inorganic hybrid perovskites (e.g., CH₃NH₃PbX₃,X=Cl,Br,I）) have attracted continuous attention in recent years due to their excellent optoelectronic properties. Luo Junhua et al., Institute of Material Structure, Chinese Academy of Sciences, prepared a new lead-free perovskite hybrid BiBr₅（TMHD=N,N,N,N- tetramethyl-1,6-hexanediammonium) single crystal by solution method, and its size reached 32×24×12 mm³（ as shown in Fig. 19 a).They then fabricated a planar array of photodetectors based on （TMHD）BiBr₅ single crystal (Figure 19b), which has a large on/off current ratio （≈10³） and a fast response speed （τ<sub> rise </sub > = 8.9 ms, τ<sub> decay </sub > = 10.2 ms)^[83]. The outstanding device performance of （TMHD）BiBr₅ illustrates that the organic-inorganic hybrid perovskite single crystal is one of the promising candidates for optoelectronic applications.

Photodetectors based on near-infrared and even shortwave infrared optoelectronic materials have potential applications in many fields, such as image sensing, optical communication, military, agriculture, remote control and environmental monitoring, and the development of optoelectronic materials with spectral response from ultraviolet to visible to infrared is a great challenge in molecular engineering^[64]. Our group has prepared a ZCC eutectic that is responsive to near-infrared light, and its responsivity is UNK 1 times higher than that of eutectic devices based on micro/nano size^[64]. Among them, the eutectic thin film photodetector has a high responsivity of 2424 mA·W^-1 in the near-infrared region, a fast response time, and a high external quantum efficiency, which is superior to other near-infrared photodetectors based on organic donor-acceptor photoactive layers^{[84⇓⇓~87]}.

The difference between microscale and macroscale crystals will lead to different applications, and molecular design based on the crystal structure of large organic molecules is an effective way to realize multifunctional materials. Organic molecular crystals display a wide range of physical properties with electronic band gaps ranging from zero to several electron volts, providing a rich platform for exploring electronic and optoelectronic functions. Large-size organic molecular crystals are grown by molecular design, and different crystal structure regulation functions and applications are changed, so that the large-size organic molecular crystals show excellent performance in the fields of long afterglow luminescence, nonlinear optical response, X-ray imaging, fast neutron detection, ferroelectricity, field effect transistors and circuits, and photoelectric detectors. The large-size long-afterglow organic luminescent crystal can show excellent enhanced long-afterglow luminescence phenomenon, the large-size organic crystal has large nonlinear coefficient and high anti-damage threshold,The continuous bandwidth of the maximum range can be obtained in the whole terahertz wave band, and the large-size organic molecular crystal is used as an output window of the ray to emit a light spot to image an object, thereby ensuring strong radiation luminous intensity,High uniformity to obtain a clear image with high resolution, and the large-size organic scintillation crystal can directly realize the detection of fast neutrons and the effective discrimination of gamma ray-neutrons,Large-size organic molecular crystals are more conducive to the integrated application of flexible and wearable devices on the human body, and the growth of large-size thin films can prepare large-area devices to meet the needs of industrial integrated applications^[15].

Through the above applications, it can be found that large-size organic molecular crystals and large-area organic molecular crystal films play an important role in the field of optoelectronics, and the change of size not only affects the change of crystal morphology, but also changes its optoelectronic properties. At the same time, it can be found that in commercial electronic devices, organic thin films are usually used instead of single crystals. However, the single crystal, as a basic unit, provides a direct way to study the structure-property relationship, and the charge transport mechanism can be studied to provide clues for molecular design. Secondly, a slight adjustment of the molecular structure may lead to huge differences in electronic properties, resulting in different applications. Finally, the introduction of large organic molecular crystals into optoelectronics, combined with the semiconductor industry, is not only a potential way to break through the limitations of existing silicon semiconductor technology, but also helps to develop new applications in the future.