Controlling Charge Recombination in Organic Photovoltaics and Photodetectors for Near-Infrared Light Conversion

The current success of organic semiconductor technology is mainly driven by the development of organic light emitting diodes (OLED), which are now routinely employed in display technologies. In the last decade, however, organic photovoltaics (OPV), leveraging the impressive improvement in device efficiency and stability, have gradually moved from a lab curiosity to a niche market. Their recent success has coincided with the rapid development of effective replacements for the fullerene-based materials that have been prevalent as electron acceptor materials until recently; namely the small molecule nonfullerene acceptors (NFAs). Through strategic design, an acceptor-donor-acceptor (A-D-A) configuration afforded highly absorbing small molecules with tunable energetics, thereby allowing the achievement of record power conversion efficiencies (PCEs) in OPVs. This relatively new class of materials offer a number of opportunities to develop new areas of research. Between those, organic photodetector (OPD), a technology based on organic photodiodes and thus closely related to OPV, is one of the most exciting. Recent efforts in the field of OPD have been focused on extending broadband detection into the near-infrared (NIR) region. The early absorption cut-off of solution processed organic semiconductors presents a challenge in achieving NIR detection, however, careful tuning of their chemical structures can help extend OPD responsivity into the infrared window. Here, we discuss how to control charge carrier recombination in organic solar cells and photodetectors for NIR light-to-current conversion for high efficiency and stable devices.