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(a) EL-voltage and (b) current-voltage characteristics of the single-layer LEDs of composites at both forward and reverse biases. (circles), (triangles), and (squares). (c) EL spectra of SWNT/MEHPPV composite LED at both forward and reverse biases of . FEL and REL represent forward and reverse EL, respectively. The dashed line is the forward EL spectrum of the undoped MEHPPV at a bias of . (d) A schematic band diagram of SWNT/MEHPPV composite LED. The work function of the SWNTs is (Ref. 20). The electron affinity and ionization potential are 2.8 and (Ref. 21), respectively, for the MEHPPV. The electrode work functions were assumed to be for the ITO and for the Al (Ref. 21).
(a) Schematic PV process at reverse bias in the SWNT/MEHPPV composite. (1) photoabsorption; (2) exciton dissociation; (3) charge conduction. (b) Photocurrent density is shown as a function of applied reverse bias for different SWNT doping concentrations in the SWNT/MEHPPV composite LEDs: (circles), (triangles), and (squares).
EL efficiency and photocurrent are shown as a function of the SWNT concentration in SWNT/MEHPPV composite LEDs. The external quantum efficiencies (EQE) of EL were measured at the current density of while the photocurrent was recorded at reverse bias and illumination of . The photocurrent density is defined as the difference between the currents measured with and without the photoillumination.
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