Abstract
We present a ternary blend-based bulk heterojunction ITO/PEDOT:PSS/PFO-DBT:MEH-PPV:PC71BM/LiF/Al photodetector. Enhanced optical absorption range of the active film has been achieved by blending two donor components viz. poly[2,7-(9,9-di-octyl-fluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PFO-DBT) and poly(2-methoxy-5(2′-ethylhexyloxy) phenylenevinylene (MEH-PPV) along with an acceptor component, i.e., (6,6)-phenyl-C71 hexnoic acid methyl ester. The dependency of the generation rate of free charge carriers in the organic photodetector (OPD) on varied incident optical power density was investigated as a function of different reverse biasing voltages. The photocurrent showed significant enhancement as the intensity of light impinging on active area of OPD is increased. The ratio of Ilight to Idark of fabricated device at −3 V was ∼3.5 × 104. The dynamic behaviour of the OPD under on/off switching irradiation revealed that sensor exhibits quick response and recovery time of <800 ms and 500 ms, respectively. Besides reliability and repeatability in the photoresponse characteristics, the cost-effective and eco-friendly fabrication is the added benefit of the fabricated OPD.
Highlights
Solution-processable organic photodetectors have attracted significant R&D efforts as a promising alternative to inorganic semiconductor devices [1,2] by virtue of their low-cost, device architectural flexibility and large-scale fabrication capability [3,4,5]
We have explored a variety of D/A combinations for the applications in organic solar cells and OPDs [10,11,12,13]
The layer stack of the fabricated OPD (ITO/PEDOT:PSS/PFO-DBT:MEH-PPV:phenyl-C71-butyric-acid methyl ester (PC71BM)/LiF/Al) and energy level diagram of the components have been depicted in Figure 2a,b, respectively
Summary
Solution-processable organic photodetectors have attracted significant R&D efforts as a promising alternative to inorganic semiconductor devices [1,2] by virtue of their low-cost, device architectural flexibility and large-scale fabrication capability [3,4,5]. The organic bulk heterojunction approach, intimately blended D/A binary blend is the dominant theme for image sensing application [6,7]. The operating principle of BHJ OPDs relies on the efficient dissociation of the photoinduced geminate carrier pairs at D/A intermolecular contacts. Photodetection parameters intensively rely on electrical properties including HOMO/LUMO energy levels, the charge carrier mobility of the donor (D) and acceptor (A). Hoppe et al report that enhanced interfacial area between D/A phases within BHJ device design enables efficient charge separation as compared to planar interface of bilayer devices [8]. The photons absorbed throughout the interpenetrating network of D/A materials contribute to the photogenerated current. Composite of judiciously chosen pair of conjugated polymer donors and acceptor material yield high photoinduced charge generation and pronounced charge transfer [9]
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