ZnO Electron Transport Layers for Scalable Nonfullerene Acceptor-Based Organic Photovoltaics: Assessing the Role of...

Solution-processed zinc oxide (ZnO) is commonly used to prepare electron transport layers (ETLs) in inverted organic photovoltaics (OPVs), but they typically exhibit a high density of intrinsic defects, which adversely affect device stability. To address this issue, magnetron sputtering is utilized to deposit ZnO ETLs. Optimized sputtering conditions lead to enhancements in device efficiency and in particular operational stability. Detailed device analysis and optical simulations suggest more efficient charge transport and extraction in PM6:Y7-BO inverted OPVs with sputtered ZnO, when compared to conventional solution-processed ZnO ETLs, resulting in an increased short-circuit current density improving from 21.9 to 23.2 mA·cm^-2 and a maximum power conversion efficiency (PCE) of 13.8%. Furthermore, green solvent and ambient air slot-die coated OPVs employing sputtered ZnO ETLs reached an average PCE of 13.9%, demonstrating the scalability of the method. Importantly, the sputtered ZnO-based devices also exhibited superior long-term stability, showing only a 10% drop in PCE after 1000 h upon exposure to illumination. These improvements are attributed to reduced shunt pathways and mitigated trap-assisted recombination, yielding stability comparable to those based on high-quality atomic layer deposited ZnO ETLs. Moreover, OPVs with sputtered ZnO consistently outperform those with solution-processed ZnO ETLs for other active layer systems, demonstrating the highest PCE of 15.9% for inverted PM6:L8-BO devices. This work highlights the potential of sputter-deposited ZnO ETLs for large-scale inverted OPVs with exceptional efficiency and stability.