Polyurethane Nanometer Islands Improving Interfacial Adhesion between the Active Layer and PEDOT:F Films in Flexible Organic Photovoltaics

Adhesion at the interfaces between adjacent layers of flexible organic photovoltaic devices (OPVs) is crucial for achieving good mechanical stability. Typically, adhesion between the solution‐processed polymer hole transport layer (such as PEDOT:F or PEDOT:PSS) and the active layer is poor. Detachment generally occurs during mechanical deformation or bending. In this work, the nanometer‐sized polyurethane islands (PUi) are fabricated to improve the adhesion between the active layer and PEDOT:F films. The PU on the active layer via solution coating exhibits an island morphology after appropriate thermal annealing, which balances the mechanical adhesion and electrical transport. During the single‐direction outward bending test, flexible OPVs with PUi maintained 82% of the initial power conversion efficiency (PCE) after 1500 bending cycles with a radius of 2 mm. Additionally, a harsher “alternating inward‐outward” bending test is designed to characterize the mechanical performance of the flexible devices. Efficiency of devices with PUi retained 85% of their initial PCE over 20 bending cycles, while the pristine devices without PUi completely failed under the same load. Furthermore, the devices with PUi displayed an efficiency retention rate of 94.3% after 100 h of maximum power point tracking under 100 mW cm −2 white light LED illumination.