Chemical Structure of QTF8 and PCBM.
(Color online) Schematic of the experiment (elements not to scale). (a) A silicon-based nanostencil is glued on the free prong of a quartz actuator, and brought in the vicinity of the surface by using a near field regulation based on the resonance modes of the system. Top contact electrodes are in situ evaporated on the bulk-heterojunction thin film through the apertures of the nanostencil silicon nitride membrane. (b) A Qplus AFM probe with a tungsten tip (grounded) is used for AFM imaging, and as a microprobe to insure the electrical connexion with the top contact electrodes. Current–voltage measurements (sample bias applied on the ITO electrode) are performed in the dark and under selective illumination at 532 nm (5 mW continuous wave laser).
(Color online) (a,b) Qplus AFM images of the Ag electrodes after insitu nanostenciling evaporation on the bulk-heterojunction thin film. Scan in closed loop mode with the nanopositioning stage, Δf = +5 Hz, Avib = 0.2 nm. (a) 70.2 × 39.7 μm2 image showing the electrodes with lateral dimensions of 20 × 20 μm2 (E1), 10 × 5 μm2 (E2), 2.5 × 12.5 μm2 (E3), and ca. 1.5 × 1.5 μm2 (E4). (b) 7 × 7 μm2 image showing the two E4 electrodes, and the submicron wide electrode (E5, ca. 4 × 0.3 μm2). (c) 3D representation of (b). Topographic profiles corresponding to the paths indicated by dotted lines in (b) are given at the bottom. Note: The electrode thickness deduced from topographic profiles is equal to ca. 26 nm for all mesoscopic patterns (E1–E4, profile shown only for E4), and to ca. 11 nm for E5.
(Color online) I–V curves recorded over the different pairs of mesoscopic electrodes (E1, E2, E3, and E4) under illumination at 532 nm (two curves per electrode size) and in dark over one of the E1 electrodes The current values under illumination at −1.5 V are ca. −40 nA for E1, −22 nA for E2, −16 nA for E3 and −2 nA for E4. The arrow pinpoints the bias voltage for which the current is equal to zero (open circuit voltage). Inset: Detail of the in dark measurement over E1 (semilog plot).
(Color online) (a) J–V curves (bias dependence of the current density) under illumination at 532 nm. J(0) values are ca. −17.5 mA/cm2 for E1, −18.8 mA/cm2 for E2, −20 mA/cm2 for E3, −30.7 mA/cm2 for E4 and −54.5 mA/cm2 for E5. (b) Current density at zero bias plotted as a function of the electrode perimeter/surface (P/S) ratio.
(Color online) Qplus AFM 1.5 × 1.5 μm2 images of the QTF8-PCBM thin film surface morphology (scan with the piezoelectric tube). (a,b) Topography and damping before annealing (Δf = +15 Hz, Avib = 0.8 nm). (c,d) Topography and damping after in situ sample annealing (Δf = +10 Hz, Avib = 0.4 nm). The topographic levels have been coded by using the same color scale (from 0 to 2.4 nm) in (a) and (c). The damping images (b) and (d) have been filtered by applying a Gaussian smooth (untreated data display similar features but with a higher noise level). (e) J–V curves recorded over E1 electrode under illumination at 532nm before (higher current density and open circuit voltage) and after the thermal treatment.
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