Nanoimprint crystalithography for organic semiconductors

Abstract

Organic semiconductor crystals (OSCs) offer mechanical flexibility, high carrier mobility, and tunable electronic structures, making them promising for optoelectronic and photonic applications. However, traditional lithographic techniques damage OSCs due to high-energy beams or solvents, leading to high defect densities, poor uniformity, and significant device-to-device variation. Existing methods also struggle to eliminate residual layers while forming independent, complex two-dimensional patterns. A chemical-free nanoimprint crystallography (NICL) method is introduced to overcome these challenges by balancing residual-layer-free nanoimprinting with the fabrication of independent, complex 2D patterns. In situ control of crystallization kinetics via temperature gradient adjustment yields OSC nanostructures with low defect densities and good uniformity. Patterning of various OSCs over a range of feature sizes is demonstrated. The patterned OSCs exhibit good lasing performance and low device-to-device variation (as low as 2%), indicating that NICL is a promising approach for fabricating high-performance, uniform OSC-based devices.

Fig. 1. Working principle of NICL.

a Schematic showing the NICL technique. b The temperature trajectories during the NICL process. The red line, green dashed line, and blue line represent the temperature of the hot end, the phase frontier, and the cold, respectively. The yellow and purple dashed line marks the melting temperature and the crystallization temperature, respectively. The inner schematics illustrate the evolution of molecular structure at different stages.

Fig. 2. NICL of OMSB molecules.

a Temperature trajectory of the hot end and cold end during NICL. The initial cooling process and post-crystallization thermal treatment process are marked with green and pink, respectively. The inset shows the undercooling temperature (ΔT_U) and normalized Raman intensity of the OMSB crystals (I_R) as functions of the cooling rate in the first cooling process. b The evolution of Raman spectra during the post-crystallization thermal treatment process. c One-dimensional diffraction peak profiles of the OMSB crystals grown at different cooling rates and temperature holding times derived from two-dimensional XRD data. d–g Two-dimensional XRD patterns of the OMSB crystals grown at different cooling rates and temperature holding time. h the summarized FWHM of (003) diffraction peak of the OMSB crystals grown at different cooling rates and temperature holding time. i Time-resolved photoluminescence of the micro-patterned OMSB arrays with different NICL parameters. The photoluminescence lifetime τ of each sample is derived with a single exponential fitting and marked in the legend. j The phase diagram summarizes the crystallinity of OSCs grown at different temperature holding times and undercooling temperatures. Different colors mark parameters that lead to different crystallinity.

Fig. 3. Size-dependency of OSC micropatterns fabricated by NICL.

a–d Top-view SEM images of OMSB micro-disks with diameter of 0.16, 30, 60, and 160 μm, respectively. e–h Side-view SEM images of OMSB micro-disks with heights of 0.44, 2.4, 4.1, and 15 μm, respectively. i Tilt-view WLI images of the OMSB micro-structures of different shapes showing uniform height and smooth surfaces. j T_set and (k) t_set as a function of the diameter of the micropatterns, respectively. The error bars represent the variability in crystallization outcomes across multiple experiments conducted under varying temperature and time conditions. They are derived from the statistical analysis of crystallinity (≥ 90%), circularity (≥ 80%, calculated as P²/4πA, where P is the perimeter and A is the area), and intact morphology without residual layers.

Fig. 4. General applicability of NICL and OMSB microlaser.

a–c, The molecular formula and PL spectra of (a) Butyl PBD, (b) DPAVB, and (c) EU (DBM)₃(phen), respectively. d–f Two-dimensional fluorescence images of (d) Butyl PBD, (e) DPAVB, and (f) EU (DBM)₃(phen) micropatterns. Scale bar: 10 μm.

Fig. 5. The Application of NICL in Optoelectronic Devices.

a Schematic of laser emission of the OMSB microdisk arrays fabricated by NICL. b The PL spectra of the OMSB microdisk at different pumping powers of 5.98, 19.02, 19.42, 22.07 μJ/cm². c The emission intensity and FWHM as functions of the pumping power. d Schematic of OFET based on patterned OSCs fabricated by NICL. e Output curves of the OFET. f The transfer curve of the OFET. g Transfer curves of 6 × 6 OFET array based on patterned OSCs fabricated by NICL. h Mobility distribution in the 6 × 6 OFET array. i Corresponding histogram of saturation mobility. The average value is 3.15 cm²V⁻¹ s⁻¹, and the standard deviation is 0.067 cm²V⁻¹ s⁻¹.