Flexible Organic Solar Cells Over 15% Efficiency with Polyimide-Integrated Graphene Electrodes

The performance of organic solar cells (OSCs) has been steadily increasing, surpassing 16% power conversion efficiency (PCE) with advances in photoactive and charge transport materials. Nonetheless, the performance of flexible OSCs still falls behind that of their rigid counterparts. Furthermore, commonly used plastic substrates are vulnerable to high-temperature annealing processes. Herein, a highly flexible and durable electrode with thermal stability achieved through direct integration of polyimide (PI) on graphene is introduced. The PI-assisted graphene electrode exhibits an ultra-clean surface together with an optical transmittance exceeding 92%, a sheet resistance of 83 U/sq, and thermal stability. Moreover, direct integration of PI improved the durability of the graphene electrode by inhibiting delamination of the graphene under mechanical stress. Using the PI- assisted graphene electrode, flexible OSC with a PCE of 15.2% was obtained with outstanding mechanical robustness. The proposed electrode is promising for use in various optoelectronic devices requiring high efficiency and flexibility.