Non-Fullerene Naphthalene Diimide-Based Electron-Transport Materials for High-Performance and Stable Perovskite Solar Cells

Halide perovskite solar cells (PSCs) have emerged as a transformative photovoltaic technology, achieving unprecedented power conversion efficiencies. However, the development of electron-transport materials (ETMs), particularly organic ETMs, has significantly trailed behind the rapid progress in hole-transport materials (HTMs). Among the organic ETMs, naphthalene diimide (NDI)-based systems stand out due to their strong electron affinity, high charge mobility, tunable energy levels, and versatile molecular design. This review systematically summarizes recent breakthroughs in non-fullerene NDI-based ETMs, with a specific focus on small-molecule compounds. Furthermore, the relationship between molecular structure, device performance, and operational stability is critically evaluated, and key challenges in interfacial engineering and charge extraction are identified. By correlating material design principles with device physics, this work provides a roadmap for advancing NDI-based ETMs to bridge the performance gap with HTMs and accelerate the commercialization of stable, high-efficiency PSCs.