Highly efficient inverted organic solar cells with natural biomaterial histidine as electron transport layer

Interfacial modification is one of the key ways to improve the performance of inverted organic solar cells (IOSCs). In this work, the performance of IOSCs with PM6:Y6 as the active layer is effectively improved by introducing the green natural biomaterial histidine to modify ITO or zinc oxide (ZnO). With the modification of histidine, ITO and ITO/ZnO films have smoother surfaces, better compatibility with the active layer, and better energy level match with the acceptor, which are beneficial to promote charge transfer and inhibit charge recombination for the IOSCs with histidine or ZnO/histidine as electron transport layers (ETLs). The power conversion efficiency (PCE) of IOSCs with histidine and ZnO/histidine as ETLs are improved to 12.10% and 16.02% along with the simultaneous increase of short circuit current density (JSC), open circuit voltage (VOC), and fill factor (FF). Meanwhile, the IOSCs with histidine or ZnO/histidine as ETLs have better stability compared to the IOSCs with ZnO as ETLs. This study suggests that natural biomaterial histidine as an ETL has capacity to improve the efficiency of IOSC by effective modification to ITO or ITO/ZnO.