Anion‐Doped Thickness‐Insensitive Electron Transport Layer for Efficient Organic Solar Cells
Zixian Liu, Haoran Tang, Hexiang Feng, Ching‐Hong Tan, Youcai Liang, Zhicheng Hu, Kai Zhang, Fei Huang, Yong Cao
Abstract
Abstract In organic solar cells, interfacial materials play essential roles in charge extraction, transportation, and collection. Currently, highly efficient and thickness‐insensitive interfacial materials are urgently needed in printable large area module devices. Herein, water/alcohol‐soluble conjugated polyelectrolyte PFNBT‐Br, with medium bandgap based on benzothiadiazole, are doped by two alkali metal sodium salts, NaH 2 PO 2 , Na 2 C 2 O 4 with different counter anions, to pursue high efficiency and thickness‐insensitive electron‐transport layers. Results show that the doping of electron‐transport material can effectively promote the performance of the devices. Moreover, electron‐transport layers doped by these salts with different counter anions show different behaviors in performances. Among which, the salt with oxalate anion C 2 O 4 2− (also named Ox 2− ) shows much better device performance than the salt with hypophosphite anion (H 2 PO 2 − ), especially under the thick film condition (e.g., 50 nm). The greatly enhanced performances of interfacial material doped by Ox 2− are due to reduced series resistance between the active layer material and the electrode, reduced dark‐current, improved charge transport, and extraction efficiency, and decreased charge recombination for the devices at thick‐film condition. These results demonstrated that n‐doping could be a great potential strategy for making thickness‐insensitive interfacial layers, besides, the performances can be further improved by carefully selecting salts.