Pressure-induced polymerization and bandgap-adjustment of TPEPA

Abstract

Organic solar cells have become an important development direction in solar cell materials because of their low cost, light weight, and good flexibility. However, the size of their bandgap is difficult to continuously regulate, resulting in a low power conversion efficiency. In this work, an organic molecule TPEPA was synthesized, and its luminescence performance and polymerization under high pressure were studied by performing in situ Raman, IR, fluorescence, and UV-vis spectroscopy. The Raman and IR spectroscopic results show that single bonds (C–H, C–Ph) and long chains (C–CC–C) are more unstable and prone to amorphization under high pressure. At 10 GPa, the TPEPA molecule undergoes a transition of amorphization accompanied by a few polymerizations in the CC bond structure. After holding pressure at 20 GPa for one day and releasing to ambient pressure, the other peaks almost disappeared, while the new peak of C(sp³)–H from the polymerization of the benzene ring was observed, indicating that the irreversible amorphization and polymerization did occur. UV-vis spectra results show that the bandgap is reduced from 2.9 eV to 1.3 eV, which is just in the maximum conversion efficiency bandgap range (1.3–1.4 eV) of p–n junction solar cell materials. This pressure is within the working pressure range of a large volume press, which is favorable in applications of large-scale synthesis. Our strategy may provide a method for the large-scale synthesis of novel organic solar cell materials.