Investigation and application of the optical field distribution in gradient organic heterojunction

Gradient organic heterojunction has emerging as a new type of semiconductors with advantages of anisotropy photocurrent output, flexibility and low material cost. Although the gradient heterojunctions are attractive to the scientific community, bottlenecks such as the difficulty in fabrication has significantly limited its further development. In this work, we have investigated in-depth mechanisms of optical field distributions inside of the gradient heterojunction. Based on the simulation model, an anisotropy photocurrent ratio was predicted when the heterojunction was designed in wedge-shaped geometry. According to the simulations, it was found that the photocurrent ratio was linear change along with the ITO displacement, where the thickness combination of donor and acceptor was tuned in gradient. In order to prove the simulation, a gradient heterojunction was fabricated based on ultra-high vacuum molecular beam epitaxy. The experimental photocurrent ratio was in accordance with the simulation. The experimental result exhibited a possibility of fabricating gradient heterojunction based on epitaxy technique. In summary, we have exhibited a possibility of gradient heterojunction structure which has potential applications in position sensing.