Design of All-Fused-Ring Nonfullerene Acceptor for Highly Sensitive Self-Powered Near-Infrared Organic Photodetectors

Sensitive
detection of near-infrared (NIR) light underpins many
important applications in academia and industry. In contrast to inorganic
counterparts, organic semiconductors exhibit favorable attributes
including solution processability, tailorable spectral response, mechanical
flexibility, and nontoxicity. However, nowadays NIR organic photodetectors
(OPDs) suffer from the scarcity of narrow-bandgap organic materials,
low NIR responsivity, and a large dark current. Herein, we developed
a novel narrow-bandgap nonfullerene acceptor, PDTTYM, and fabricated
four OPD devices based on PDTTYM matched with four different polymer
donors, which exhibited remarkable responsivities approaching 0.5
A W–1 in the NIR region ranging from 890 to 910
nm. By adjusting the bulk-heterojunction layer thicknesses in four
OPD devices, we optimized the dark current densities (Jds) and the external quantum efficiencies of devices to
get the optimized devices. Furthermore, we use Mott–Schottky
analysis to evaluate the charge doping densities and depletion widths
of four devices, which may explain the different dark current characteristics
of our OPDs. All four optimized OPDs exhibit large specific detectivities
around 1012 Jones for the NIR spectral region ranging from
780 to 1050 nm, which is close to that of a conventional commercial
Si-based photodetector.