ABSTRACT
Electrical doping has long played a role in studies of conjugated polymers. Thus, for example, metallic levels of conductivity in polyacetylene were obtained by halogen doping in the 1970s [1], and PEDOT:PSS [2], in which a poly(3,4-ethylenedioxythiophene-1,5-diyl) main chain is partially oxidized (p-doped) and charged-compensated by an anionic polymer, is widely used as a hole-injection layer for organic light-emitting diodes (OLEDs). In contrast, until recently, the active layers of organic electronic devices, such as OLEDs, organic field-effect transistors (OFETs), and organic photovoltaics (OPVs), have generally been based on undoped organic semiconductors. However, in recent years, there has been a tremendous growth of interest in the controlled doping of organic semiconductors using molecular redox agents for the above-mentioned applications [3–31], as well as for thermoelectrics [32–36], and for use in hybrid devices such as lead halide perovskite solar cells [37–40], where doping can increase conductivity and improve carrier injection and collection at electrodes. In this chapter, we first examine the basic doping process in organic molecular and polymeric materials, we then discuss factors to be considered in selecting a dopant, survey some of the molecules that have been used as dopants, and, finally, discuss some case studies of the use of doping to improve device performance.
