Mechanical properties and densification behavior of pentacene films pressurized by cold and warm isostatic presses

• We apply isostatic pressing to improve mechanical properties of porous pentacene films.
• Although most pores are obviously crushed, film thickness reduction is nondetective.
• The nondetection is attributed to original dense cylindrical structure of as-coat films.
• Indentation modulus and hardness of isostatic press films are reduced by up to 25% and 23%.
• Critical bending radius of the isostatic press films, 4.29 mm, is still the same as that of the as-coat films.

Mechanical properties such as bending strength represent critical issues for the manufacture and practical use of flexible organic semiconducting films. In this study, we have used isostatic presses to densify pentacene films and compared the densification behavior and mechanical properties of the films. Although most pores formed between the grains were crushed in the pressed films, thickness reduction of the films was nondetective. And the nondetection is attributed to original dense cylindrical structure of the as-coated films which is predicted to produce a porosity 9.3% and a thickness reduction 80 nm. Both the indentation modulus (15.0 GPa) and the indentation hardness (0.643 GPa) of the as-coated films were reduced by up to 25% and 23% in the WIP films. The resultant critical bending radius of the WIP films of 4.29 mm is approximately the same as that of the as-coated films because of simultaneous falls in both modulus and hardness. The decreasing modulus and hardness in the isostatically pressed films are concluded to be caused by relaxation of the pentacene grain anisotropy accompanied by buckling of the grains.

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