Abstract
Organic photodetectors (OPDs) with a near-infrared (NIR) response beyond 900nm are intriguing electronics for various applications. It is challenging to develop NIR OPDs with high sensitivity and fast response. Herein, the acceptor materials of OPDs are tuned to extend detection to ≈1100nm with improved sensitivity. A new fused ring electron acceptor, ICS (2,2'-((2Z,2'Z)-(((4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl)bis(4-((2-ethylhexyl)thio)thiophene-5,2-diyl))bis(methaneylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile), is developed with alkylthio thiophene as the bridge, achieving a small bandgap of 1.35eV while decreasing dark current densities under reverse bias. By further introducing a secondary acceptor of PC61BM, the doping compensation, and unfavored hole injection blocking enable further improvement of detectivity. The PTB7-Th (Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl]): ICS: PC61BM OPDs deliver a low dark current density of 1.23 × 10-9 A cm-2, a high peak specific detectivity of 1.09 × 1013 Jones at 950nm under -0.2V, and a fast response speed with a -3dB bandwidth of 720kHz biased under -2V. The photoplethysmography system with the PTB7-Th: ICS: PC61BM OPD can reliably monitor heartbeats under 980nm NIR light. This study promises the development of organic NIR OPDs with high detectivity and fast response by tuning active materials.
Published Version
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