Design and Application of an Asymmetric Naphthalimide-based Molecule with Improved Hydrophobicity for Highly Stable Organic Solar Cells

With the photovoltaic efficiency of organic solar cells (OSCs) exceeding 17%, improving the stability of these systems has become the most important issue for their practical applications. In particular, moisture in the environment may erode the interlayer molecules, which has been proved to be the main reason for the efficiency decay. At present, the development of moisture-resistant interlayer molecules remains a great challenge to the field. Herein, we designed two naphthalene diimide (NDI)-based organic compounds, namely, NDI-M and NDI-S, exhibiting suitable energy level and excellent electron extraction property. In addition to this, NDI-S has extremely low hygroscopicity. An efficiency of 17.27% was achieved for the NDI-S inverted cells, and the long-term stability under continuous illumination conditions was significantly improved with a T80 lifetime (the time required to reach 80% of initial performance) of over 28 000 h. More importantly, we demonstrated that, by using a covalent bond to link the counter ions with the host molecular structure in the zwitterion, the asymmetric molecule NDI-S can transform from amorphous to crystalline hydrate at high humidity and exhibited outstanding non-hygroscopic nature; this could decrease the interaction between the cell and the moisture, obviously improving the device stability under high humidity.

Automated summary

The stability of organic solar cells (OSCs) is crucial for their practical applications. This study focuses on addressing the stability issue by designing two organic compounds with suitable energy level and excellent electron extraction property. The results show significant improvement in device stability under high humidity conditions, with an achieved efficiency of 17.27% and a T80 lifetime of over 28,000 hours.