Effect of core on photovoltaic performance of naphthalimide interlayer materials

In this study, we designed and synthesized three naphthalimide (NI)-based organic cathode interlayer materials (CIMs) with different electron-donating cores—that is, N2FN, NEDOT, and NDTP cores. As the size and electron-donating ability of the cores increased, the CIMs exhibited enhanced thermal stabilities with increased decomposition temperatures, red-shifted and enlarged absorption spectra, and elevated molecular orbital energy levels. The N2FN with a fluorinated thiophene core exhibited the strongest self-doping effect and intermolecular π stacking, leading to the highest electron mobility and the poorest surface contact. By contrast, the NEDOT and NDTP with steric cores exhibited relatively low self-doping intensity and large d-spacing of π-π stacking but demonstrated smooth surface morphologies and good electric contact with low series resistance. Finally, binary organic solar cells (OSCs) based on the NDTP interlayer exhibited a power conversion efficiency of up to 18.5%, which was higher than those of N2FN (15.3%) and NEDOT (17.8%) cores. This study reveals that the core method is an effective way to design efficient NI-based CIMs for high-efficiency non-fullerene OSCs. We synthesize three new organic cathode interlayer materials with different electron-donating ability and size of central cores for organic solar cells (OSCs), and demonstrate NDTP interlayer modified OSCs exhibit the best photovoltaic performance.