Complex formation of ferrocene derivatives with electron transport layers enables improved performance and photostability in organic solar cells

Electron transport layers (ETLs), e.g., metal oxides, organic small molecules, or conjugated polymers, play a vital role in both performance and photo-thermal stability in organic solar cells (OSCs). Herein, we explored hybrid organic-inorganic electron transport materials by forming complexes between typical electron transport layers and ferrocene (Fc)-based molecules. Experimental and theoretical investigations revealed van der Waals interaction between the ETL and Fc compounds, which allows fine-tuning of the electrode work function to improve charge extraction properties and reduce trap-assisted recombination. As a result, OSCs showed improved fill factor (FF) and power conversion efficiency (PCE) for five donor-acceptor blends and three ETLs, with FF and PCE exceeding 80% and 20.1%, respectively. Finally, we demonstrated improved photostability for the hybrid ETLs with devices that retained 80% of their initial performance for 700 h when degraded under operating conditions (ISOS-L-1I).