Double-sided asymmetric surface modification of ZnO interfacial layer to enhance performance in organic solar cells

Surface modification of the widely used ZnO interfacial layer is a crucial issue for the development of photoelectric devices toward high efficiency and long-term stability. Most conventional surface modifications of ZnO interfacial layers involve only a one-sided modification (e.g., a ZnO/active layer interface), which limits the electrical and electronic performance of the resulting interfacial layer. Herein, we report a double-sided surface modification strategy in which both sides of the ZnO interfacial layer are modified. The resulting double-sided modified ZnO layers are used to enhance the photovoltaic performance of inverted organic solar cells as electron-transporting layers (ETLs). Compared with devices based on unmodified ZnO interfacial layers, the power conversion efficiencies of devices using the modified ZnO interfacial layer are markedly enhanced, from 3.42% to 4.23% for the P3HT:PC61BM active layer, and from 7.57% to 8.61% for the PTB7:PC71BM blend system. The enhancements in photovoltaic performance result mainly from the modified energy level alignment and improved interface contact quality between the ETL and active layer, which help to reduce the interfacial energy barrier between the active layer and indium tin oxide electrode, thereby enhancing the electron collection and transport efficiency. More importantly, this double-sided surface modification strategy could be easily extended to modify the interfacial layers of other photoelectric devices, such as perovskite solar cells, quantum dot solar cells and organic light-emitting diodes.