Design, synthesis and characterization of Naphthalene Diimide small molecules as electron transport materials for perovskite solar cells

Electron transporting materials (ETM) are critical to the stability and performance of perovskite solar cells. Organic small molecule ETMs have several advantages such as low cost, high purity, good processability, high modifiability and high conductivity. In this work, a series of Naphthalene diimide (NDI) derivates were synthesized and characterized in terms of energy levels by cyclic voltammetry and UV-VIS spectroscopy, thermal stability, and hydrophobicity. Good energy level alignment with the perovskite crystal were found for all axially substituted NDI derivates, while the relation between molecular structure and thermal stability was investigated, finding good stability for rigid, aromatic-substituted NDIs. Perovskite solar cells were fabricated with the synthesized ETMs, comparing them to a reference NDI. One of the synthesized materials showed higher efficiency than the reference material, while two others had lower performances.