| AVS 58th Annual International Symposium and Exhibition | |
| Energy Frontiers Focus Topic | Wednesday Sessions |
| Session EN+NS-WeM |
| Session: | Organic Photovoltaics |
| Presenter: | Benjamin Leever, Air Force Research Laboratory |
| Authors: | B.J. Leever, Air Force Research Laboratory I.P. Murray, Northwestern University M.F. Durstock, Air Force Research Laboratory T.J. Marks, Northwestern University M.C. Hersam, Northwestern University |
| Correspondent: | Click to Email |
The fabrication process for bulk heterojunction (BHJ) organic photovoltaic (OPV) devices nearly always includes anode modification steps ranging from solvent cleaning to haloacid treatments to the deposition of interfacial layers such as polymer blends or transition metal oxides. The role of these treatments is not yet fully understood, but they are thought to modify the anode work function, contribute to electron-blocking, alter the anode surface energy, and prevent shunts among other functions. In separate work, conductive atomic force microscopy (AFM) and derivative techniques have been used to simultaneously probe both the morphological and electrical properties of BHJ photovoltaic layers. Previous work has demonstrated a correlation between BHJ nanostructure and properties such as photocurrent at the same scale (~ 20 nm) as the phase separation in these films. Photocurrent variability has also been observed at a length scale orders of magnitude larger the domains in the BHJ layer, and this variation has been speculated to have an origin in the anode or interfacial layers in the OPV architecture.
In this work, a correlation between indium tin oxide (ITO) surface treatment and spatially localized photocurrent variation has been found in OPV devices with a poly(3-hexylthiophene):[6,6]-phenyl-C-61-butyric acid methyl ester (P3HT:PCBM) BHJ layer. Atomic force photovoltaic microscopy (AFPM) was used to scan arrays of functioning 2 μm solar cells with varied ITO surface treatments. The standard deviation of the average photocurrent was found to be 11.4% for devices fabricated on untreated ITO, 8.6% for devices with a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) interlayer, and 6.7% for devices with a HCl-treated ITO surface. These results suggest that conductive non-uniformity in the ITO surface is transferred through the P3HT:PCBM film and that improving the anode conductive uniformity could be an important role of OPV interfacial layers or anode surface treatments.