Charge Carrier and Spin Transport Properties in Diketopyrrolopyrrole‐Based Polymers

Abstract

ABSTRACT The organic active layer in organic spin‐valves (OSVs) plays a vital role in regulating the device's performance, and the variations in molecular structure can significantly modulate their physicochemical properties. Herein, we synthesized two diketopyrrolopyrrole‐based donor‐acceptor copolymers with distinct alkyl side chains, namely DPP‐BTCN‐C1 (with side‐chain branching points closer to the conjugated skeleton) and DPP‐BTCN‐C3. To evaluate the charge carrier transport properties, a polymer field‐effect transistor and space charge limited current method based on the two molecules were conducted. The experimental results demonstrated that the DPP‐BTCN‐C1 materials had a higher electron transport mobility. Moreover, the spin transport properties were also revealed by fabricating OSVs devices. In the OSVs with a 50 nm interlayer, DPP‐BTCN‐C1 exhibited a higher magnetoresistance (RM) value of up to 24.6 %. By fitting the polymer thickness dependence of the MR value at 10 K, a longer spin diffusion length and higher spin polarization injection efficiency were achieved for the DPP‐BTCN‐C1 structure. We attributed the differences in charge and spin transport performance to the modulation of the film microstructure and energy levels by the alkyl side chains. This work studied the structure‐property relationship of polymer OSVs from the perspective of side‐chain engineering, providing valuable insights for the design of polymers with enhanced spin properties.