Cathode Interlayer Engineering with Vacuum Thermal Evaporated N-type Rylene Diimide Derivatives in Highly Efficient Inverted Perovskite Solar Cells

Abstract

In inverted perovskite solar cells (PeSCs), choosing cathode interlayer plays key role in determining performance of solar cell. Among various processing methods, vacuum thermal evaporation (VTE) is already adopted in electron transporting layer (ETL) such as C60 and cathode interlayer such as bathocuproine (BCP), LiF and Ca in inverted PeSCs. Especially, cathode interlayer have been already utilized to suppress the interfacial resistance and lower the energy barrier between ETL and cathode. N-type rylene diimide derivatives such as perylene diimide (PDI) and naphtahlene diimide (NDI) have attracted great attention due to their advantages of easy molecular modification, high electron mobility and good thermal and chemical stability so that have been applied to cathode interlayer by solution processing such as spin-coating method. In this study, we demonstrate for the first time rylene diimide derivatives such as PDI and NDI family organic small molecules as cathode interlayer candidates using VTE method. Rylene diimide derivatives films show thin thickness about ~5 nm. In comparison with widely used BCP, underlying rylene diimide materials exhibit different silver cathode growth phenomenon. In addition, we compare the effect as a cathode interlayer by considering the energy levels and metal cathode growth phenomenon by the number of amine-functionalized groups of each material. Consequently, the PeSC with N,N'-Bis[3-(dimethylamino)propyl]perylene-3,4,9,10-tetracarboxylic diimide (PDIN) shows a enhanced power conversion efficiency (PCE) of 21.60%, which is higher than that of the PeSC without cathode interlayer and with BCP or NDI-based interlayer. Excluding the solvent consideration in solution processing, PDI-based materials that are easily vacuum thermal evaporated are expected to be in the spotlight in inverted PeSCs for cathode interlayer.