Paper NS1+PV-TuA10
Locally Probing the Efficacy of Photoinduced Charge-Generation and Trap Clearing in Pentacene-Based Thin-Film Heterojunctions and Transistors using Electric Force Microscopy

Tuesday, November 10, 2009, 5:00 pm, Room A8

Pentacene and its derivatives are leading candidates for many organic electronics applications including electron donors in organic photovoltaics. Charge trapping, which is associated with device degradation in both photovoltaics and transistors, remains poorly understood even in this comparatively well studied class of materials. Northrup and Chabinyc [1] have carried out ab initio studies showing that reactions of holes with hydrogenated and oxygenated pentacene is a plausible charge trapping mechanism. Jaquith et al. [2] demonstrated a dependence of trap formation rate on hole concentration in pentacene, which is consistent with traps forming by a defect-mediated chemical reaction, and showed that traps could be cleared by the application of light. Coffey and Ginger [3] have shown that the fastest charging rates under illumination in polymer/fullerene films do not occur at phase interfaces, as widely assumed. Charge generation at the donor-acceptor interface in organic heterojunctions also remains poorly understood.

To resolve such open questions, we have developed a general approach to illuminating samples (from above) in an electric force microscope. We will describe studies where variable-wavelength light is utilized to clear traps in polycrystalline pentacene transistors. We will also discuss investigations into image charge generation in bis(thienyl)-pentacene/PCBM bulk heterojunction thin films.

[1] J.E Northrup and M.L. Chabinyc, Phys. Rev. B 68, 041202 (2003).

[2] M.J. Jaquith, E.M. Muller, and J.A. Marohn, J. Phys. Chem. B 111, 7711 (2007).

[3] D.S. Ginger and D.C. Coffey, Nat. Mater. 5, 735 (2006).