Reduced interface losses in inverted perovskite solar cells by using a simple dual-functional phenanthroline derivative

Interface losses at metal/organic interface is a critical issue in organic electronic devices. The interfacial layers play a significant role in enhancing the device performance and the interfacial material design criteria are ongoing challenges to be faced in optimization the device performance. In this work, a simple Phenanthroline derivative Phen-I was synthesized through a quaternization reaction in a high yield without complicated purification process. Besides its good wettability and compatibility of the contact between metal electrode and organic layer, interestingly, Phen-I displays a dual functional property, i.e., it not only lowers the work function of the metallic cathode to increase electron extraction but also can be doped into electron transporting material to enhance the conductivity. The inverted perovskite solar cells (PSCs) with Phen-I as cathode interlayer (CIL) show superior performance both in power conversion efficiency, with a maximum PCE of 18.13%, and devices stability as compared with the control devices. Encouragingly, the best PCE of 19.27% was obtained when the perovskite layer based on FA(0.3)MA(0.7)PbI(2.7)Cl(0.3) perovskite system. Meanwhile, the devices with Phen-I as CIL show low J-V hysteresis during the forward and reverse bias sweeping. Subsequent studies demonstrate that the performance of the inverted PSCs also improves to 15.25% using 5% Phen-I: PC61BM as electron transporting layer (ETL). Herein, the interface between the metal electrode and ETL is carefully investigated using a series of electrical and surface potential techniques. These results demonstrate that Phen-I is a dual-functional interlayer material to reduce interface losses, which, highlights the broad promise of this new class of materials for applications in organic electronic devices. Meanwhile, owing to the simple molecular structure, low-cost and solution processible, these intriguing features render Phen-I more suitable for efficient organic electronics in large area printing process.