The identification, characterization and mitigation of defect states in organic photovoltaic devices: a review and outlook

In any microelectronic device, fundamental physical parameters must be well understood for successful electronic optimization. One such prominent parameter is energetic trap states, which are well-known to plague amorphous or otherwise impure semiconducting materials. Organic semiconductors are no strangers to such states and their electronic properties are evidently tied to these defects. Herein, this article discusses the identification, characterization and mitigation of bandgap residing trap levels in organic photovoltaic devices. A compilation of select studies to date is given and a general outlook is proposed. Organic photovoltaic materials are depicted as multiple trap-level systems with a seemingly continuous distribution of electronic states throughout the bandgap. Some elucidations as to the origins of these electronic states as well as recent works centered on defect removal are also presented. This report comprehensively reviews the identification, characterization, mitigation and effects of electronic defect levels in organic photovoltaic devices.