Enhanced Electron Mobility and Interfacial Properties by Introducing Nitrogen and Sulfur Heteroatoms into Naphthalene Diimide-Based Electron Transport Materials for Inverted Perovskite Solar Cells: A Theoretical Study

In perovskite solar cells (PSCs), the electron transport layer (ETL) plays an important part in the extraction and transport of photogenerated electrons in the perovskite layer. Electron transport materials (ETMs) also modify the interface between the perovskite layer and the electrode, reducing charge recombination. In this work, a series of ETMs based on the experimentally synthesized N,N′-bis(1-indanyl) naphthalene-1,4,5,8-tetracarboxylic diimide (NDI-ID) [Kwon, O. P. et al. Adv. Funct. Mater. 2020, 30, 1905951] were designed by introducing thiophene sulfur and pyrrole nitrogen atoms in the N-substituent side chain. The effects of heteroatom engineering on electronic properties, transfer, and interfacial properties were systematically studied. We found that the designed ETMs have improved the electronic properties. More significantly, compared to the NDI-ID molecule, the electron mobility of the ETMs is significantly increased, even exceeding 26 times. Especially, NDI-ID-1S-m exhibits remarkably stronger interfacial interactions with MAPbI3 and enhanced electron extraction capability compared with NDI-ID. Our results demonstrate that heteroatom-regulated NDI small molecules are potential ETMs and offer helpful guidance for the design of durable and efficient components for PSCs.