Revealing the Unusual Efficiency Enhancement of Organic Solar Cells with Polymer-Donor-Treated Cathode Contacts

The metal oxides with low trap density of states as the electron transport layer are crucial for the high performance of the organic solar cells (OSCs). It is universally acknowledged that modifying n-type metal oxide contacts with polymer donors will harm the carrier extraction on account of the mismatched energy level. However, we find that modifying interlayer consisting of the alcohol amines with some polymer donor additive can unusually enhance the performance of the OSCs. Compared with triethanolamine (TEA) passivated ZnO, TEA:polymer donor treated ZnO shows lower trap density and enhances electron mobility resulting in higher current density in OSC devices. Here, we reveal that the enhanced oxygen-defect passivation ability of TEA with polymer additive is attributed to the enhanced negative electrostatic potential of TEA owing to the hydrogen bond formation between the polymer and the hydroxyl group in TEA. This strategy that enhancing the negative electrostatic potential of the passivators for improving oxygen defect passivation can be extended to other types of organic electronic devices.