Conjugated Polyelectrolyte with Long-Range Ordering and Compact Molecular Packing as Hole-Transporting Material for Efficient and Flexible Organic Solar Cells.

Hole-transporting layer (HTL) materials with a non-corrosive nature and good compatibility with flexible electrodes are highly desirable for advancing efficient and flexible organic solar cells (OSCs). Conjugated polyelectrolytes (CPEs) exhibit intriguing advantages as HTLs, such as tunable properties and excellent solution processability, but they suffer from poor charge-transporting properties, resulting in inferior performance to traditional HTLs. Herein, a series of pH-neutral CPEs are designed and synthesized that can form enhanced crystalline and highly ordered films. By tailoring trifluoromethyl substituents on the triphenylamine unit, TMPT-F exhibited exceptional long-range molecular ordering and compact laminar packing, along with a crystalline coherence length of 2.56 nm and a laminar packing distance of 1.48 nm, ultimately yielding an unprecedented conductivity of 3.3 × 10-2 S m-1 for the CPE-based HTL. The substantially enhanced charge-transporting property of the PMA-doped TMPT-F:PMA greatly suppressed the charge recombination in OSCs. The OSC modified by the TMPT-F:PMA HTL exhibited a PCE as high as 19.24%, which is superior to the PEDOT:PSS device. Moreover, TMPT-F:PMA showed excellent compatibility with flexible electrode, enabling a PCE of 16.52% for flexible OSC, and the device retained 83% of the initial PCE even after a 500-cycle bending at 5 mm radius.