Nanostructured thin films for organic photovoltaic cells and organic light-emitting diodes

Achieving efficient organic optoelectronic devices, such as organic photovoltaic (OPV) cells and organic light-emitting diodes (OLEDs), relies on the understanding of the formation of various organic nanostructures as well as the fundamental of physical processes in device operation. The research presented in this thesis systematically investigates the controlled growth of organic nanostructure through different approaches and their relationship to OPV cell performance. Moreover, new materials and device structure are explored to achieve efficient OLEDs, which also provide further insight of the physical processes governing the performance of these devices.;We first investigated the phase separation process in a molecular mixed donor-acceptor (D -- A) bulk heterojunction (BHJ) composed of pentacene and C60 suing a combination of experimental and computational approaches. Both experiment characterization and the MD simulation reveals that strong aggregation of pentacene exists in the pentacene:C60 mixtures due to the strong pi -- pi interaction among pentacene molecules. By controlling the processing conditions to suppress the pentacene aggregation to nanoscale leads to higher device efficiency as the more photogenerated excitons are able to reach the D -- A interface and contribute to the photocurrent. To circumvent the limits on phase separated D -- A mixed heterojunction, an interdigitated D -- A BHJ is synthesized through the oblique angle deposition (OAD) of copper phthalocyanine (CuPc). The morphology of CuPc nanorod arrays grown under the OAD process can be controlled by careful selection of the processing conditions, and we have achieved a high density, vertically aligned, polycrystalline CuPc nanorod array with nanorod size as small as 20-30 nm. Successful infiltration of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) into the optimized CuPc nanorod arrays has resulted in doubling of the power conversion efficiency of the OPV cell over planar heterojunction device based on the same D -- A materials.;We also show that the efficiency of a deep-blue phosphorescent OLED (PHOLED) can be significantly enhanced by improving the exciton and charge confinement in the multilayer organic stack. A peak external quantum efficiency of (20 +/- 1) % is achieved, which approaches the theoretical maximum of PHOLED without specific out-coupling mechanisms. We further demonstrate PHOLEDs with enhanced power efficiency by using the p-i- n device structures to reduce driving voltage and achieved a maximum of (14 +/- 1) lm/W and (12 +/- 1) lm/W at a luminance of 100 cd/m 2. Moreover, an ultra low turn-on voltage of ∼ 1.3 V is observed in an orange-emitting polymer light-emitting diode (PLED) using ZnO nanoparticles as the electron injection layer. An Auger-assisted electron injection mechanism is proposed to explain the low turn-on voltage. The novel ZnO nanoparicles electron injection layer opens a new way to reduce driving voltage in PLED. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html)...