Investigation of the effect of the active layer composition of organic photosensitive structures with a bulk heterojunction based on fullerene and non-fullerene acceptors on spectral characteristics

The spectral characteristics of organic photosensitive structures based on fullerene and non-fullerene acceptors were investigated. Structures based on the conjugated polymer PBDTT-DPP in combination with the fullerene acceptor PC71BM and the non-fullerene acceptor ITIC-F were fabricated, and their spectral and photoelectric characteristics were studied. It was shown that the structure based on the binary blend PBDTT-DPP:PC71BM exhibits limited sensitivity (11 mA/W at 796 nm) due to the small offset between the lowest unoccupied molecular orbital levels of the donor and acceptor. The replacement of the acceptor with the non-fullerene ITIC-F, which possesses a deeper lowest unoccupied molecular orbital level, allowed the spectral range to be extended to 1000 nm and the maximum photosensitivity to be increased to 100 mA/W (at 825 nm), however, a dip was observed in the spectrum at 800 nm. To eliminate this drawback, a photosensitive structure based on the PBDTT-DPP:PC71BM:ITIC-F blend was developed. It was established that the introduction of the fullerene acceptor into the binary blend based on PBDTT-DPP:ITIC-F eliminates the spectral dip in photosensitivity and facilitates stepwise charge carrier transfer. As a result, the developed structure exhibits a spectral response in the wavelength range of 400–950 nm, high photosensitivity of 130 mA/W (at 818 nm), and improved electrical characteristics. It has been demonstrated that the use of a combination of fullerene and non-fullerene acceptors in the active layer of the structure allows increasing the sensitivity of organic photosensitive structures.