Phenanthroline-Based Low-Cost and Efficient Small-Molecule Cathode Interfacial Layer Enables High-Performance Inverted Perovskite Solar Cells via Doctor-Blade Coating

Perovskite solar cells (PSCs) have recently emerged as highly efficient and cutting-edge photovoltaic technology. In inverted PSCs, challenges are focused on the insufficient interface contact and energy level misalignment between the electron transport layer (ETL) and the metal electrode. Hence, the cathode interfacial layer (CIL) plays a crucial role in regulating energy levels and enabling charge extraction in PSCs. In this study, a low-cost phenanthroline derivative, 4,7-dimethoxy-1,10-phenanthroline (Phen-OMe), is developed as an efficient CIL between the PCBM and Ag electrodes. The incorporation of Phen-OMe not only improves the interfacial contact but also effectively reduces the work function (WF) of the Ag electrode, thus promoting charge dissociation and transport at the interface. Through utilizing a wide-band-gap perovskite with the band gap of 1.77 eV as the active layer by a simple, high-throughput, and low-cost doctor-blade coating process, the power conversion efficiency (PCE) is enhanced significantly from 16.11% of the control device to 18.61% of the device with Phen-OMe as the CIL. Interestingly, Phen-OMe shows a broad application as the CIL in PSCs and tandem solar cells (TSCs), resulting in a boosted efficiency of 22.29% in intermediate-band-gap PSCs and a PCE of 22.05% with a high open-circuit voltage (V-OC) of 2.12 V in the perovskite/organic TSC. This achievement shows that Phen-OMe would be a potential candidate as low-cost and efficient CILs for PSCs.