Organic electronics research has focused primarily on flexible, inexpensive versions of traditional semiconductor technologies. Although mixed ionic/electronic conduction in conjugated organic materials introduces exciting functionality, the understanding of the fundamental processes that take place is still in its infancy. In this Research News article, the advantages, applications, and basic research needs that relate to the incorporation of ionic carriers in organic electronic materials and devices are discussed and placed in the broader context of the field.

A p–n junction in an organic emissive polymer is chemically fixed through the use of polymerizable ions. This leads to a permanent configuration of compensating ions, unlike dynamic light‐emitting electrochemical cells. The process is demonstrated with red‐, green‐, and blue‐light‐emissive polymers; a photovoltaic effect is also demonstrated.

3866 www.MaterialsViews.com wileyonlinelibrary.com upon oxidation due to anion insertion and contract upon reduction due to anion expulsion or 2) contract on oxidation due to cation expulsion and expand on reduction due to cation insertion. Actuators based on CPs can be electrically controlled at low operating voltages (typically 1-3 V), continuously switched between expanded/ contracted states, and operate well in liquid electrolytes. Interfacing CPs with biological systems is also possible due to the demonstrated biocompatibility in vitro and in vivo . [ 5,6 ] To date, record-breaking CP actuators have been demonstrated to generate stresses as large as 100 MPa [ 7 ] and strains up to 40%, [ 8 ] although the generation of both high stress and high strain has yet to be achieved. Typical CP actuators can generate smaller, yet still notable, stresses of 1-5 MPa with strains on the order of 2%. [ 9 ] These impressive values have led to commercial interest in the development of several types of biomedical devices utilizing CP actuators. [ 1,9 ] However, current optimized device designs are not ideal for applications requiring implantation in vivo . Major diffi culties encountered when fabricating CP-based actuators arise from the fact that the bulk polymers are brittle and insoluble due to the extended conjugated backbone, which restricts the molding or processing of these materials into 3D structures. Therefore, the majority of CP-based actuators are synthesized via electropolymerization directly onto metal foils, [ 1 ] where the metal is often retained in the fi nal device. While metal incorporation helps minimize the iR drop across CP fi lms, these devices are typically limited to 2D fi lm architectures and have signifi cant problems with delamination. [ 10,11 ] While useful for surgical and external biomedical applications, incorporation of non-degradable or rigid components [ 1,12 ] that are incompatible with soft tissues severely limit the possible applications of CP actuators. In addition, device performance in a biologicallyrelevant environment is still unclear as the majority of studies utilize optimized electrolyte systems that employ toxic salts or organic solvents.To avoid the use of metals or rigid inorganic components in the fi nal device, all-polymeric actuators have been constructed by depositing CPs in situ during chemical polymerization onto several types of synthetic backing materials such as PVDF, [13][14][15] crosslinked PEO-based copolymers, [16][17][18][19][20] and polyurethane. [ 21 ] Single-component, metal-free, biocompatible, electromechanical actuator devices are fabricated using a composite material composed of silk fi broin and poly(pyrrole) (PPy). Chemical modifi cation techniques are developed to produce free-standing fi lms with a bilayer-type structure, with unmodifi ed silk on one side and an interpenetrating network (IPN) of silk and PPy on the other. The IPN formed between the silk and PPy prohibits delamination, resulting in a durable and fully biocompatible device. The electroch...

We report the synthesis of a soluble perylene-based small molecule for use as an n-type emissive material for organic optoelectronic device applications, and demonstrate the material in a light-emitting electrochemical cell configuration.

We study electrochemical p- and n-type doping in the well-known light-emitting polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). Doping reactions are characterized using cyclic voltammetry. Optical measurements including photoluminescence and UV/Vis/NIR transmission were performed on doped samples. We find that oxidation in MEH-PPV is a highly reversible reaction resulting in stable freestanding doped films, while the reduced form is unstable and the reaction irreversible. We discuss the dependence of doping reactions on scan rate, film thickness, salt type and concentration, and working electrode type. We observe the development of two additional broad absorption bands in both lightly and heavily doped films accompanied by a slight blueshift in the primary optical transition, suggesting bipolaron band formation. Finally we find that both p and n dopings result in extremely sensitive photoluminescence quenching. We propose a physical model for understanding electrochemical doping in MEH-PPV and the implications this has on the development of such technologies as polymer light-emitting electrochemical cells, electrochromic devices, actuators, and sensors.