Coexistent Integer Charge Transfer and Charge Transfer Complex in F4-TCNQ-Doped PTAA for Efficient Flexible Organic Light-Emitting Diodes.

Understanding the mechanism of interaction between organic polymers and dopants is of great significance to further enhance the performances of flexible electronics. Here, the two doping mechanisms of charge transfer complex (CTC) and integer charge transfer (ICT) are found to coexist in p-π conjugated PTAA doped with the strong acceptor F4-TCNQ, and their correlation is affected by the HJ-aggregate state of the doped polymer. The growth of the J-aggregate caused by the increase of CTC would lead to a corresponding formation of ICT. The doping efficiency was dominated by the CTC/ICT ratio. On the basis of the analysis of the optical, electrical, and morphological properties of PTAA:F4-TCNQ films, we optimized the CTC/ICT ratio to achieve the efficient hole transport layers that are used in solution-processed flexible phosphorescent organic light-emitting diodes with p-i-n structure. The optimal device presents a very high current efficiency (CE) of 31.12 cd/A and a low turn-on voltage of 3.6 V.