Enhancing Stability and Performance in Perovskite Solar Cells through Rationally Designed Phenanthro[9,10- <i>d</i> ]imidazole Derivatives for Tailored Interfacial Engineering

Interfacial engineering plays a significant role in advancing the performance and stability of perovskite solar cells (PSCs). In inverted PSCs, nickel oxide (NiO_<i>x</i>) is widely used as a hole transport material (HTM). However, poor interactions at the NiO_<i>x</i>/CH₃NH₃PbI₃ (MAPbI₃) interface often lead to reduced device stability and power conversion efficiency (PCE). To address this issue, dopant-free ultrathin interfacial layers (IFLs) have been introduced between NiO_<i>x</i> and the perovskite layer to enhance the interfacial interactions and optimize the device performance. In this work, phenanthro[9,10-<i>d</i>]imidazole derivatives, SR-1 and SR-2, were rationally designed and synthesized as IFL materials in p-i-n devices with a device configuration of indium tin oxide (ITO)/NiO_<i>x</i>/IFL/MAPbI₃/PCBM/BCP/Ag. These IFLs not only modify the energy levels of NiO_<i>x</i> but also improve the surface morphology and crystallinity of MAPbI₃, effectively passivate interfacial defects, facilitate charge extraction, and reduce trap density at the NiO_<i>x</i>/MAPbI₃ interface. As a result, the PCEs of both devices with SR-1 and SR-2 IFLs outperformed those of the pristine device. The best performance of 20.3% efficiency with nearly negligible hysteresis was achieved from the device with SR-1. Furthermore, the devices with SR molecules achieved remarkable thermal stability under continuous heating at 60 °C and 50-60% relative humidity, highlighting the potential of SR-based IFLs for stable and efficient PSCs.