Conjugated polymers: Long and winding polymeric roads

Poorly ordered films of conjugated polymers that show high charge mobility recently challenged the idea that disorder is detrimental for electrical conduction. Systematic studies now reveal that long polymeric chains can bridge small crystalline domains thus supporting charge transport on length scales relevant for device operation. Contrary to small conjugated molecules that form tightly packed molecular crystals with an outstanding structural order and high charge mobilities, conjugated polymers consist of long and semiflexible chains of small molecules (conjugated cores) linked together by chemical bonds. Charges can move along these chains, like electrons in wires. When conjugated polymers aggregate in solid films, the chains usually form complex and frequently inhomogeneous morphologies, composed of disordered (amorphous) regions and some ordered domains, where the conjugated cores are packed similarly to small-molecule crystals.