| Although organic photovoltaic (OPV) devices have shown drastic improvements in their efficiencies in the last decade, there are still performance issues that need to be addressed for OPV to be competitive with other more mature photovoltaic technologies in the field of alternative energy. In this thesis, we investigated several novel device architectures with an aim of increasing the overall OPV performance and understanding the factors that influence the device degradation.;First, the archetypical polymeric, solution-based poly(3-hexylthiophene):[6,6]-phenyl-C 61-butyric acid methyl ester (P3HT:PC61BM) OPV devices were fabricated in our laboratory for the purposes of 1) benchmarking with vapor-deposited small-molecule OPV devices and 2) evaluation of the applicability of performance enhancement methods that have been developed for small-molecule OPVs to polymeric OPVs. The methods applied to P3HT:PC61BM OPVs were: 1) reduction of the donor concentration to generate a Schottky-like interface between the anode buffer layer molybdenum oxide (MoOx) and PC61BM, which is expected to produce a higher open circuit voltage (Voc), and 2) addition of silicone-based additives to induce crystallization and phase separation, which is aimed at increasing the short-circuit current density (Jsc). We found that although the Voc increased with the reduction of the P3HT concentration, the Jsc was simultaneously reduced as the contribution of the donor in the photocurrent generation decreased. For the additive experiment, a decrease in device performance was observed. However, absorption measurements suggest an increase in crystallinity, similar to thermal annealing treatments.;Second, several device architectures were used to determine the pathway by which the triplet dopant platinum octaethylporphyrin (PtOEP) enhances the performance of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/C 60 photovoltaic devices. Possible pathways include 1) the extension of the exciton diffusion length (LD) of MEH-PPV and 2) the dopant PtOEP acting merely as an additional absorber. Devices with varied thicknesses of the PtOEP doped MEH-PPV donor layer as well as PtOEP concentration were evaluated. Enhancement in photocurrent responses was observed in the MEH-PPV absorption region, regardless of the MEH-PPV:PtOEP donor layer thicknesses or the PtOEP concentrations. LD values were obtained from a model that supports the extension of triplet LD by PtOEP as a triplet sensitizer in MEH-PPV/C60 OPV devices. In addition, experiments incorporating a blocking layer between MEH-PPV and C60 were able to confirm the role of PtOEP in photogeneration. The enhancement in the photocurrent spectral response with doped donor layers, although small, can be attributed to the extension of LD in MEH-PPV rather than direct absorption by the PtOEP dopant.;Finally, self-assembled monolayers (SAMs) based on octylphosphonic acid (C8PA) and 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctylphosphonic acid (PFOPA) were investigated for application as an anode buffer layer in OPV devices. It was found that the degradation of the OPV efficiency with respect to air exposure was significantly reduced with the perfluorinated PFOPA compared to aliphatic C8PA. The OPV degradation was attributed to moisture diffusion from the top aluminum electrode and the lowering of the anode work function as a result of hydrolysis of the SAM buffer layer. |
