Electrical scanning probe microscopy of an integrated blocking layer.

Scanning probe microscopy was performed on an integrated blocking layer system developed for hybrid organic solar cells. A nanocomposite consisting of titania and an amphiphilic triblock copolymer ((PEO)MA-PDMS-MA(PEO)) was prepared by sol-gel chemistry. After plasma treatment and annealing of a spin casted film of 30-100 nm thickness a granular structure with a typical titania grain diameter of 20 nm was found. Conductive scanning force microscopy revealed that on top of almost every grain on the surface there is an increased conductivity compared to the average value. The correlation of grains and conductivity indicated that titania particles formed interconnecting paths through the film. For the resistivity of these pathways we found that effects of tip-sample and sample-electrode resistivity dominate. Additionally, conductive scanning force microscopy revealed non-conducting structures attributed to the thermal treatment. Kelvin probe microscopy of pristine samples on one side and plasma treated plus annealed samples on the other side showed that there is a shift in work function (0.8 +/- 0.2 eV) as expected for the transition of amorphous to anatase titania.