Benzo[ghi]perylenetriimide derivatives as effective interfacial passivation and electron transporting layers for inverted perovskite solar cells

In this study, we synthesized three benzo[ghi]perylenetriimide (BPTI) derivatives-C4, C3A, and C3AI-having butyl, dimethylaminopropyl, and propylammonium iodide side chains, respectively, and applied them as electron-transport layers (ETLs) and interfacial layers for inverted planar perovskite solar cells (PSCs) and examined their ability to function as defect passivation agents. Our PSC structure was glass/indium tin oxide/ NiOx/CH3NH3(MA) PbI3/BPTI/PCBM/BCP/Ag. We used X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, UV-Vis spectroscopy, X-ray diffraction spectroscopy, field-effect scanning electron microscopy, and atomic force microscopy to determine the optoelectronic properties of PSCs prepared with and without the BPTIs. We found that the BPTI derivatives interacted with the perovskite and altered its energy levels to enhance electron extraction in their respective devices. In particular, C3AI effectively passivated the surface defects of perovskite and decreased the interfacial resistance, thereby suppressing the hysteresis effect and improving the device performance. We obtained an optimized power conversion efficiency (PCE) of 20.3% for the C3AI-containing MAPbI3 device, with a remarkable fill factor of 80.0%-among the highest ever reported for an MAPbI3-based p-i-n PSC. Therefore, this paper provides a new strategy of using nonfullerene materials for dual functions (as ETLs and defect passivation) in PSCs.