Polymorphic Structures and Crystal Growth Kinetics in TCTA Thin Films

doi:10.16553/j.cnki.issn1000-985x.2025.0165

Abstract

Abstract: 4，4'，4″-tri（N-carbazolyl） triphenylamine（TCTA） is a widely used organic semiconductor material in optoelectronic devices， whose crystallization behavior significantly influences device photoelectric performance. However， a comprehensive understanding of its polymorphic structures and crystal growth kinetics remains lacking. In this study， the formation conditions of polymorphs and their growth kinetics in TCTA thin films were systematically investigated using polarized optical microscopy （POM） and atomic force microscopy （AFM）. The results reveal the coexistence of two polymorphs with markedly different melting points. Notably， only Form Ⅰ with a lower melting point is observed when the film thickness is below 80 nm. Crystal growth kinetic analysis demonstrates that the low-melting-point polymorph exhibits faster growth rates and lower activation energy. This study deepens the understanding of crystallization behavior in TCTA thin films and provides valuable insights for tailoring their microstructure and homogeneity to improve the device performance.

Key words: TCTA; thin film; polymorphism; crystal growth kinetics; film thickness; activation energy

CLC Number:

O795

YAO Zhiyuan, YANG Yuhui, ZUO Biao. Polymorphic Structures and Crystal Growth Kinetics in TCTA Thin Films[J]. Journal of Synthetic Crystals, 2026, 55(1): 37-45.

Figures/Tables 6

Fig.1 Characterization of morphology and Tg of TCTA thin films. （a） Optical microscopy image of TCTA thin film， inset shows chemical structure of TCTA molecule；（b） AFM image of TCTA thin film；（c） normalized thicknessversus temperature for TCTA thin films with different initial thicknesses；（d） relationship between Tg and film thickness of TCTA thin films

Fig.2 Morphology of two distinct crystals in TCTA thin film. （a） Optical microscopy image of two different crystals；（b），（c） AFM images of Form Ⅰ and Form Ⅱ crystals， respectively；（d），（e） morphology of edges of Form Ⅰ and Form Ⅱ crystals， respectively；（f），（g） height profiles corresponding to lines marked in （d） and （e）， respectively

Fig.3 Morphological evolution optical microscopy images of melting process of two TCTA crystals after heat treatment at 269 ℃ （a） and 296 ℃ （b） for varying durations， respectively

Fig.4 Polymorphic distribution maps of TCTA thin films with different thicknesses observed by POM at different temperatures

Fig.5 Crystal growth kinetics and activation energy for two polymorphs of TCTA. Optical microscopy images showing isothermal growth of Form Ⅰ （a） and Form Ⅱ （b） crystals at 180 ℃；（c） evolution of crystal radius versus time for both polymorphs at 180 ℃；（d） temperature dependence of crystal growth rates for both polymorphs

Fig.6 Film thickness dependence of isothermal growth rates of two polymorphs of TCTA. Evolution of crystal radius versus time for Form Ⅰ （a） and Form Ⅱ （b） in TCTA thin films of different thicknesses；（c） dependence of crystal growth rates on film thickness for Form Ⅰ and Form Ⅱ

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