Ecofriendly Cellulose Substrate‐Based Flexible Transparent Electrode for Flexible Organic Solar Cells with Efficiency Over 18%

Flexibility is a key advantage of organic solar cells (OSCs), and the power conversion efficiencies (PCEs) of flexible OSCs (FOSCs) are primarily constrained by flexible transparent electrodes (FTEs). While much attention has been devoted to the study of conductive layers on FTEs, the importance of flexible substrates in influencing the properties of FTEs and the performance of FOSCs is often overlooked. In this study, an FTE is developed using an eco‐friendly ethyl cellulose (EC) substrate and silver nanowires (AgNWs) as the conductive electrode. The FTE exhibits a high transmittance of up to 88% at 550 nm and a low sheet resistance of 17.65 Ω/□. Consequently, FOSCs based on the EC/PI FTEs achieve a remarkable PCE of 18.05%, comparable to that on the rigid ITO substrate. The flexible devices also demonstrate excellent bending and peeling durability even under extreme bending conditions.