New materials and fabrication techniques and their utilization in organic photovoltaic devices

This work has two distinct, but similar, objectives. Both objectives relate directly to improved understanding and performance of organic photovoltaics (OPVs). The first projects objective is to address the origin of the Voc in order to improve device performance through the use of a family of new materials, Subphthalocyanines. The second projects objective is to implement an alternative device fabrication technique (Layer-by-Layer deposition) with the goal of improving device performance by controlling the architecture of a bulk heterojunction OPV.;Subphthalocyanines exhibit strong absorption in the visible region and extinction coefficients similar to that of copper phthalocyanine (CuPc). Oxidation and reduction potentials of subphthalocyanines indicate they may be a suitable donor-like material in OPV cells employing C60 as the acceptor-like material. A double heterostructure OPV cell has been fabricated using boron subphthalocyanine chloride (SubPc) as the donor-like material and C60 as the acceptor-like material. The SubPc/C60 cell showed a more than doubling of Voc compared to a conventional CuPc/C60 cell under 1 sun AM1.5G simulated illumination. The substantial increase in Voc is attributed to an increase in the energy difference between the lowest unoccupied molecular orbital (LUMO) of the acceptor-like material and the highest occupied molecular orbital (HOMO) of the donor-like material (referred to as the interface gap, I g). In addition, peripheral substitution of SubPc has been shown to alter the reduction and oxidation potentials of the material, which, in turn, alters the HOMO and LUMO energies. Incorporating the substituted SubPcs as the donor-like or acceptor-like materials in PV cells should allow us to vary the value of Ig and further explore the significance of Ig on Voc.;Layer-by-Layer (LbL) deposition utilizes electrostatic interactions of charged polyelectrolytes to grow thin-film multilayers. This deposition process allows for greater control of the thin film architecture compared to spin cast deposition or thermal evaporation methods, thereby making it an attractive technique for fabrication of OPV devices. There are a few factors that affect the growth of the multilayer thin-films: polyelectrolyte solution concentration, dipping time, and the pH of the polyelectrolyte solution. The goals of this work were to understand the growth regimes of the thin films under different growth conditions and utilize the LbL deposition method to fabricate OPV devices.