Parts-Per-Million-Level Doping Effects and Organic Solar Cells Having Doping-Based Junctions

Abstract

Controlling the pn-type behavior of a semiconductor such as silicon by adding an extremely small quantity of an impurity (doping) has been a central part of inorganic semiconductor electronics since the 20th century. Recent progress in the doping of organic semiconductors strongly suggests the advent of a new era of doped organic semiconductors. In this chapter, the principles and effects of doping at the level of parts per million (ppm) in organic semiconductor films and in single crystals are summarized. This chapter includes descriptions of complete pn-control, doping sensitization, ppm-doping effects in organic single crystals measured by the Hall effect. The Wannier excitonic doping of organic single crystals possessing band conduction and the defect science of organic single crystals related to carrier trapping and scattering are introduced as a new scientific field. In addition, organic junctions made by ppm-doping technology are summarized. The pn-homojunctions in the single films as well as the D/A co-deposited films and the ohmic junctions at organic/metal and organic/organic interfaces, which are indispensable to fabricate novel organic solar cells, are described.