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(a) Absorbance of solution (black, top) and approximately 7 nm thick film on ITO-coated glass (red, bottom). The strong peak at 1055 nm indicates nearly monochiral (7, 5) nanotubes. Inset: scanning electron micrograph of a (7, 5) nanotube film on ITO-coated glass. Scale bar is 100 nm. (b) Intensity of photoluminescence from solution (top) and film (bottom) on quartz as a function of excitation and emission wavelengths. The strong, narrow peak at (1055, 660) is indicative of nearly monochiral (7, 5) nanotubes, with small contributions by (6, 5) (1000, 570), (10, 2) (1090, 740), (7, 6) (1150, 670), and (8, 6) (1200, 710) apparent in the solution photoluminescence. The photoluminescence arising from film exhibits limited exciton energy transfer, most prominently from (6, 5) to (7, 5) at (1050, 590), and from (7, 5) to (7, 6) and (8, 6) at (1200, 655).
External QE from nanotube/C60 device stacks with C60 thickness of 50 nm (blue), 70 nm (green), and 86 nm (red) compared to the AM1.5G photon flux (black). The external QE is modulated by the optical interference and depends strongly on C60 thickness (see Ref. 25 ).
(a) Optimization of external QE at λ = 1055 nm as a function of the relative thickness of the nanotube layer. The dashed line represents the linear regime within which the internal QE was found by Bindl et al. to be 85% (see Ref. 20 ). Inset: device architecture: (1) ITO-coated glass; (2) (7, 5) nanotube film; (3) C60; (4) BCP; (5) Ag. (b) Optimization of AM1.5G photovoltaic parameters Jsc (blue diamonds), Voc (red triangles), FF (green circles), and ηP (black squares) at 1.0 sun as a function of the relative thickness of the nanotube layer. (c) Current density–voltage curves from the device exhibiting maximum power conversion efficiency in part (b) in the dark (black) and under AM1.5G 100 mW cm−2 illumination (red). (d) Photovoltaic parameters, using the same symbols as (b), adjusted for and plotted against corresponding AM1.5G intensity. ηP = 0.95% and 1.02% at 1.0 and 1.5 suns, respectively.
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