Qualified interlayer modifier for organic solar cells with optimized interfacial topography and boosted efficiency based on biomass-derived acid

The cathode interlayer modification is crucial for the performance of organic solar cells (OSCs), which ensures an efficient electron extraction. However, the research progress of the cathode interlayer is seriously lagging behind, compared with the emerging of OSCs. In this research, three different biomass-derived acid, oxalic acid, azelaic acid and tannic acid, are investigated as the modifiers for the PDIN cathode interlayer of the non-fullerene acceptor based OSCs. The best performance is obtained via the modification of oxalic acid, due to its small conjugated molecule structure. It improves the cathode interlayer quality without disrupting the intermolecular stacking of PDIN. After the modification of oxalic acid, the energy barrier between the active layer and the cathode interlayer is reduced and the carrier recombination is suppressed. It helps the formation of a good ohmic contact and enhances the electron collection. Therefore, the average power conversion efficiency increases from 17.61% of the control device to 18.28%, with a champion efficiency of 18.43%. This research first demonstrates the application of biomass-derived acid in the cathode interlayer modification. It offers a novel strategy to achieve high-efficient cathode interlayer for OSCs using biomaterials.