Organic parallel grouping crystals without grain boundary

Abstract

Organic crystal-based micro/nanostructures with morphology-driven photons/electrons transport characteristics demonstrate exceptional potential for the development of optoelectronic functional materials. However, the construction of continuities and lossless interfaces within multicomponent structures remains a significant challenge, primarily due to inherent material differences and current technology limits. Herein, organic parallel grouping crystals (OPGCs), which devoid of grain boundaries between crystals via a solution viscosity-induced binuclear co-growth strategy, are designed to enhance photon transmission efficiency. Notably, the symbiotic phenomenon among components within OPGCs is precisely regulated by manipulating the solvent viscosity to exceed 0.5 mPa·s through adjustments in factors such as the cooling rate, solvent type, concentration. Compared with the low photon transmission efficiency (2.1%) caused by the discontinuous splicing interface, the elimination of grain boundaries significantly enhances the interlayer photon transmission efficiency of OPGCs, resulting in an overlap degree-dependent adjustable transmission efficiency ranging from 21.3% to 54.9%. This symbiotic strategy demonstrates universality to small molecules, coordination compounds, and cocrystals, enabling the construction of parallel grouping structures comprising single- or multi-component crystals.

Fig. 1. Illustration of the growth process of OPGCs.

Schematic illustrations depicting the preparation of the OPGCs via a previous epitaxial growth process with the grain boundary between materials, and b the current co-growth process without the grain boundary between materials.

Fig. 2. Elaborate control and growth mechanism of OPGCs.

a Schematic illustration of the co-growth process for organic parallel grouping microcrystals. b SEM image of a typical organic parallel grouping microcrystal. Scale bar: 10 μm. c TEM image of an individual parallel grouping microcrystal. Scale bar: 500 nm. d–f SAED patterns of the corresponding parallel grouping microcrystal labeled as “1” d, “2” e, and “3” f in c. The scale bars are all 2 1/nm. Crystal face indices g and molecular packing arrangement h of a single microrod. i, j Crystal face indices i and molecular packing arrangement j of the parallel grouping microrod. k SEM images of organic parallel grouping microrods with increasing overlapping length from left to right. l Distribution of the overlap degree (ω) of parallel grouping microstructures at different cooling rates.

Fig. 3. Co-growth processes of the OPGCs.

a Molecular dynamics simulations of the nucleation process of parallel grouping microstructures. b Energy curve corresponding to the molecular dynamics simulation in (a). c FM images for the co-growth process of parallel grouping microstructures obtained at different times.

Fig. 4. Synthesis of OPGCs based on viscosity control.

a–f FM images of organic microrods with increasing parallel grouping frequency as the solvent viscosity (η) increases. g Time-dependent viscosity curve at different cooling rates; the solvent was DCM and the initial concentration was 20 mmol/L. h Concentration-dependent viscosity curve in different solvents. i Relationship between the frequency of parallel grouping crystal and the solvent viscosity.

Fig. 5. Overlapping degree-dependent interlayer photon transmission efficiency of OPGCs.

a Bright-field micrograph illustrating the crystal splicing process through a probe. b Schematic representation of the hierarchical microstructure through mechanical splicing at the interface (left), and parallel grouping crystal through the co-growth process without grain boundary (right). c Spatially resolved PL spectra obtained from output channels in the spliced crystal. Inset: i FM image of the spliced crystal. ii FM image collected from the spliced crystal by excitation with a laser beam at a distance of 20 μm from OIII. d, e Spatially resolved PL spectra obtained from tips in parallel grouping crystals with different overlapping degree. Inset: i FM images of parallel grouping crystals. ii FM images collected from the parallel grouping microstructures by excitation with a laser beam at a distance of 20 μm from OIII. f Overlapping degree-dependent PL intensity at different optical output channels. g Interlayer photon transmission efficiency versus overlap degree of parallel grouping crystals.

Fig. 6. Universality of co-growth strategy for organic systems.

a Chemical structures and FM images of single molecules including 1–4 for single structures (top) and parallel grouping structures (bottom) based on single crystal. b Chemical structures of the cocrystal component molecules including 5–9 (acceptors) and 10–13 (donors) as well as FM images of single structures and parallel grouping structures based on cocrystals. c₁ Schematic representation of the heterogeneous integration of the parallel grouping microstructure. c₂–c₄ FM images of cocrystals 6&13 c₂, and 9&13 c₃, parallel grouping heterostructure 6&13&9 c₄. c₅ SEM image of parallel grouping heterostructure 6&13&9 corresponding to c₄. d CIE chromaticity diagram of these single crystals and cocrystals in a and b.