A bird's eye view of the synthesis and practical application of conducting polymers

Hydrolysis of doped conducting polymers

Conducting polymers display a range of interesting properties, from electrical conduction to tunable optical absorption and mechanical flexibility, to name but a few. Their properties arise from positive charges (carbocations) on their conjugated backbone that are stabilised by counterions doped in the polymer matrix. In this research we report hydrolysis of these carbocations when poly(3,4-ethylenedioxy thiophene) is exposed to 1 mM aqueous salt solutions. Remarkably, two classes of anion interactions are revealed; anions that oxidise PEDOT via a doping process, and those that facilitate the S_N1 hydrolysis of the carbocation to create hydroxylated PEDOT. A pKa of 6.4 for the conjugate acid of the anion approximately marks the transition between chemical oxidation and hydrolysis. PEDOT can be cycled between hydrolysis and oxidation by alternating exposure to different salt solutions. This has ramifications for using doped conducting polymers in aqueous environments (such as sensing, energy storage and biomedical devices).

Tuning, optimization, and perovskite solar cell device integration of ultrathin poly(3,4-ethylene dioxythiophene) films via a single-step all-dry process

For semicrystalline poly(3,4-ethylene dioxythiophene) (PEDOT), oxidative chemical vapor deposition (oCVD) enables systematic control over the b-axis lattice parameter (π-π stacking distance). Decreasing the b-axis lattice parameter increases the charge transfer integral, thus enhancing intracrystallite mobility. To reduce the barrier to intercrystallite transport, oCVD conditions were tailored to produce pure face-on crystallite orientation rather than the more common edge-on orientation. The face-on oriented oCVD PEDOT with the lowest b-axis lattice parameter displayed the highest in-plane electrical conductivity (σdc = 2800 S/cm), largest optical bandgap (2.9 eV), and lowest degree of disorder as characterized by the Urbach band edge energy. With the single step oCVD process at growth conditions compatible with direct deposition onto flexible plastic substrates, the ratio σdc/σop reached 50. As compared to spun-cast PEDOT:polystyrene sulfonate, integration of oCVD PEDOT as a hole transport layer (HTL) improved both the power conversion efficiency (PCE) and shelf-life stability of inverted perovskite solar cells (PSC).