Processing behaviors of thin-film pentacene and benzene-1,4-diboronic acid in supercritical carbon dioxide

This research investigates the feasibility of using supercritical carbon dioxide (scCO2) as a green solvent for processing organic thin film semiconductor, such as pentacene, and a potential molecular modifier for use in electronic device applications. Benzene-1,4-diboronic acid (BDBA) was selected as a molecular modifier in this work due to its electron deficient nature, which can potentially enhance pentacene's physical, chemical or electronic properties by changing its structure in the solid state. In this study, the solubilities of BDBA and pentacene in scCO2 are measured as individual compounds and as co-solutes, at 313 K, using ultraviolet (UV) spectroscopy. Methanol co-solvent effects on solubility have also been characterized for each compound. The results show that BDBA is insoluble in pure scCO2 up to 1.82 × 107 Pa. However, with a small amount of methanol added to the mixture, BDBA becomes soluble in solution with a solubility of 3.81 × 10− 4 mol/l at 9.00 × 106-Pa-pressure. In contrast, pentacene is only soluble in scCO2 at pressures above 1.10 × 107 Pa, and its solubility is decreased upon addition of methanol due to the non-polar nature of pentacene. When a pentacene thin film is treated with BDBA in scCO2/methanol solution, BDBA sorption is observed at pressures as low as 8.80 × 106 Pa. Based on these results, it is concluded that treatment of pentacene thin films in scCO2 is a promising approach that can be optimized for BDBA and other similar molecular modifiers, to produce multi-component organic thin film devices.