Natural Dextran as an Efficient Interfacial Passivator for ZnO-Based Electron-Transport Layers in Inverted Organic Solar Cells

Compared to conventional organic solar cells (OSCs) with acidic PEDOT:PSS as the hole transport layer (HTL), inverted OSCs (i-OSCs) with zinc oxide (ZnO) as the electron transport layer (ETL) display significant advantages in terms of high stability. However, an obvious limitation in i-OSCs is that the sol-gel processed ZnO layers possess detrimental defects at the interface, which hinders the improvement of its photovoltaic performance. To address this problem, a natural, and green dextran (Dex) is used as an efficient interfacial passivator to modify the ZnO layer, thereby achieving enhanced device performance in i-OSCs. The introduction of the Dex passivator efficiently suppresses the interfacial recombination loss, resulting in higher power conversion efficiencies (PCEs). Interestingly, Dex-passivated ZnO exhibits broad applications as an ETL for different types of i-OSCs, including fullerene, non-fullerene, and all-polymer OSCs, in which the D18:Y6 system gives the highest PCE of 18.32%. This is one of the highest values reported for binary i-OSCs. Moreover, the application of Dex significantly improves the device stability, and the T₈₀ lifetimes based on PM6:Y6, D18:Y6, and PM6:PY-IT exceed 1500 h. These results imply that Dex is an excellent interfacial passivator for ZnO-based ETL for high-efficiency and stable i-OSCs.