Ionic moieties in organic and hybrid semiconducting devices: Influence on energy band structure and function

The interaction between ionic moieties and the electronic properties of organic and hybrid semiconductors can yield a variety of interesting and sometimes surprising effects. Ionic moieties can induce interface dipoles, support electrochemical doping and lead to band-bending. The dynamic motion of ions under electric fields and the induced changes in conductivity can make it difficult to de-convolute the various mechanisms at play. This review attempts to provide a perspective on different types of interactions between ions and semiconductors and goes into depth addressing the application of solution-processed polyelectrolyte and oligoelectrolyte materials to control the energy band structures and behaviour of organic and hybrid semiconducting optoelectronic devices. This review introduces and highlights different types of ionic materials (such as conjugated polyelectrolytes and molecular ionic dopants) that have been used to achieve different effects (such as creating interfacial dipoles, vacuum energy shifts, changes in Fermi energies and doping) in organic and hybrid semiconducting devices before going into greater depth with the emerging class of non-conjugated polyelectrolytes and oligoelectrolytes and provides a comprehensive summary of recent progress using these materials in semiconducting devices. This class of materials has been receiving increasing attention recently and provides insights into the fundamental effects of ionic functionalities on the energy band structures and functions in organic and hybrid semiconductors.