Device physics and operation of lateral bulk heterojunction devices.

Measurements of lateral bulk heterojunction (BHJ) devices have recently been reported as a means to characterize charge transport and recombination properties within organic photovoltaic (OPV) materials. These structures allow for the direct measurement of the lateral extents of the space charge regions, potential and electric field profiles, current versus voltage characteristics, and other physical and chemical properties. This article describes numerical simulations that show three different transport regimes present within lateral BHJ devices and two different experimental methods, which verify those findings. These measurement techniques utilize typical confocal microscopy tools as well as steady-state current versus voltage measurements on high aspect ratio nanofabricated structures in order to probe the material properties between the electrodes. Experimental results show that the lateral extents of space charge regions within these devices are approximately 1-5 µm, which are related to the drift lengths of the charge carriers, and that the mechanism of bimolecular recombination is shown to be a bulk material property. The results within this article describe a series of methods to evaluate charge transport and recombination along the in-plane direction in BHJ films and provide complementary insights to those obtained from vertical-device-based measurements.

Scanning photocurrent microscopy of lateral organic bulk heterojunctions.

Scanning confocal photocurrent microscopy has been used to characterize carrier collection efficiency in lateral bulk heterojunction devices. By analyzing the photocurrent mappings within these devices, the lateral extents of the space charge regions has been measured and reported. Modulation via white light bias or increased voltage bias is also shown to increase the size of the space charge regions.