Enhancement of exciton properties in poly(3-hexylthiophene) via carbon nitride composites

Once the efficiency of solar energy-converting devices depends on the population of the electron–hole pairs (excitons), one way of increasing the conversion efficiency of photoactive materials is using electron-accepting materials, which acts on the separation efficiency of these pairs by collecting the electrons. In such a way, carbon nitride (C₃N₄) has been studied as an electron acceptor. With simple synthesis and easy tailoring properties, this material becomes a promising candidate in organic photovoltaic cells. Thus, the objective was to evaluate the photocurrent as a function of exciton properties. Then, P3HT was obtained by redox polymerization and C₃N₄ by urea pyrolysis. Photoelectrochemical and spectroscopic measurements were performed to characterize the electrodes. In addition, theoretical calculations were carried out using TD-DFT. It was observed that a photocurrent 3-fold increased in relation to the pure P3HT film (from 12.1 up to 33.2 µA cm^-2), attributed to the increase in the hole-electron separation efficiency, with an increase in their lifetime (from 0.18 to 0.42 ms). The electron transport was also boosted (an increase of 2.1 \(\times \) $\times$ 10^-3 cm² V^-1 s^-1). The theoretical calculations suggest that the structural modification of C₃N₄ affects the photocurrent due to the charge delocalization induced by the torsion of the triazine units. Besides, the photocurrent values achieved in this work were not expressive; the results pointed out that the association P3HT+C₃N₄ is promissory. The further optimization of these systems by heat treatment, type of solvent, and deposition method could lead to better results. Additionally, the theoretical results demonstrated that minor system modifications could improve the photocurrent values.

The synergetic effect of the composite obtained between poly(3-hexylthiophene) and carbon nitride in the appropriate proportion leads to a 3-fold increase in photocurrent due to the improvement in the properties of the photogenerated excintons.