Ultra‐Thin Flexible ITO‐free Organic Solar Cells with Gradient Bilayer Electron Transport Materials

Ultrathin flexible organic solar cells (OSCs) have garnered widespread attention in wearable electronic devices for their lightweight and excellent conformability. Silver nanowires (AgNWs) are one of the most widely used bottom electrodes because of their high conductivity and transmittance. However, the high roughness of AgNWs on the flexible substrate exerts adverse effects on device performance. To address this critical issue, a bilayer electron‐transport‐materials (ETMs) strategy consisting of an indium‐doped zinc oxide (IZO) and a pristine ZnO is developed. The IZO is utilized as the first layer of ETM, which can effectively fill voids in AgNWs to form a high‐conductive composite electrode. The ZnO is used as the second layer of ETM, facilitating charge extraction. The ultrathin flexible OSCs prepared based on the gradient bilayer ETMs can achieve a power conversion efficiency (PCE) of 16.1%, associated with improved mechanical stability, showing a PCE retention of 93% after 10 000 bending cycles ( R = 1 mm) and 82% under 1000 compression (30%)‐release cycling test. To the best of knowledge, it's one of the highest efficiency for ultrathin (less than 10 μm) flexible OSCs based on the solution‐processed electrodes. This work will provide a new avenue for fabricating high‐performance and mechanically robust ultraflexible ITO‐free OSCs.