(34b) Conjugated Macrocycles for Ultra-Sensitive Organic Photodetectors

Organic photodetectors (OPDs) are attractive for their high optical absorption coefficient, broad wavelength tunability, and compatibility with light-weight and flexible devices. One critical parameter that limits OPD's performance is the high dark current, because it determines the noise current level and sensitivity of an OPD. I will introduce a new molecular design that enables ultra-sensitive organic photodetectors. We use a rigid, conjugated macrocycle as the electron acceptor in devices to obtain high photocurrent and low dark current. The macrocycle consists of redox-active diphenyl perylenediimides that are wrapped into a tetrameric structure. We make a direct comparison between the devices made with the macrocyclic acceptor and an acyclic control molecule; we find that the superior performance of the macrocycle originates from its rigid, conjugated, and cyclic structure. The macrocycle’s rigid structure reduces the number of charged defects originating from deformed sp² carbons and covalent defects from photo/thermo-activation. With this molecular design we are able to suppress dark current density while retaining high responsivity in an ultra-sensitive non-fullerene OPD. Importantly, we achieve a detectivity of ~10¹⁴Jones at near zero bias voltage. This is without the need for extra carrier blocking layers commonly employed in fullerene-based devices. Our devices are comparable to the best fullerene-based photodetectors, and the sensitivity at low working voltages (< 0.1 V) is a record for non-fullerene OPDs.

References:

[1] J. Am. Chem. Soc. 2016, 138 (39), 12861-12867.

[2] J. Am. Chem. Soc. 2016, 138 (50), 16426-16431.