Doping of organic semiconductors: Insights from EPR spectroscopy

Abstract

Doping, here understood as purposefully introducing charge carriers, is a standard procedure, which is regularly employed with semiconductors to enhance conductivity and, hence, improve efficiency. Organic semiconductors are no different here, only the ratio of a dopant to a host is dramatically different compared to their inorganic counterparts. Therefore, doping of organic semiconductors will often affect the morphology and the conductivity of the host material. As the charge carriers created upon doping are usually paramagnetic, electron paramagnetic resonance (EPR) spectroscopy is perfectly suited to investigate the doping process, providing unique insights due to its exclusive sensitivity to paramagnetic states and high resolution on a molecular scale. To make an impact, EPR spectroscopy needs to be applied routinely to a large series of different systems, and the data obtained need to be analyzed in a reliable and robust way. This strongly advocates for using conventional X-band cw-EPR spectroscopy at room temperature wherever possible. Questions that can be addressed by EPR spectroscopy are discussed, and this Perspective presents how the method can gain greater importance for addressing the urgent research questions in the field, mainly by automating both data acquisition and analysis and developing robust and reliable analysis tools.