| dc.description.abstract | The lower production costs of organic photovoltaic (OPV) solar cells vs. traditional inorganic architectures could provide a more cost-effective alternative for the solar power industry. We studied layered OPV samples of P3HT:PCBM/ZnO/ITO/glass employing surface photovoltage (SPV) measurements. The SPV experiments were performed via the Kelvin probe approach in a vacuum chamber filled with a 100% nitrogen gas at atmospheric pressure. The data was collected both as a function of time for a polychromatic illumination and as a function of photon energy for a monochromatic illumination. ZnO/ITO/glass and ITO/glass structures were also probed as control samples. The P3HT:PCBM/ZnO/ITO/glass specimens were synthesized with variations of growth/deposition/processing temperatures of both P3HT:PCBM and ZnO. The addition and variations of synthesis conditions of the active layer produced significant changes in the observed "light-on" and "light-off" SPV transients, which revealed fast and slow charge recombination processes (in contrast with, e.g., the ZnO/ITO/glass samples yielding only one "standard" recombination time). Presence of the active layer and its growth conditions also dramatically affected the SPV spectroscopy data. Furthermore, both the transient and spectral SPV results were dependent on the growth/deposition conditions of the ZnO layers. The multiple processes on different timescales indicate the presence of several pathways for surface/interface charge recombination. Whether the long-term recession of the voltage-against-time values is a factor of the specimens or due to atmospheric adsorption or some other cause is yet to be determined and requires further study. Polysulfone, a high-strength thermoplastic, possesses a variety of applications such as dielectric material, membranes, filters, space travel, and microfluidics. First, we developed a reliable method to create thin polysulfone films of varying thicknesses through spin coating on n-doped silicon substrates. After enough suitable samples were prepared with thin films of various thicknesses, the samples were subjected to surface photovoltage testing. The introduction of the polysulfone layer caused a red-shifting of the silicon band gap as well as creating more features in the near-infrared spectral region. The polysulfone also caused a reverse in the polarity of the short-term transient process of the surface under illumination. Under the influence of ultraviolet light, polysulfone reverses its normal hydrophobic nature to a hydrophilic state for a limited time. Measurement of such a surface revealed more short-term transient features under illumination as well as the accentuation of the near-infrared features attributable to polysulfone. Whether the transient features unique to the UV-exposed surface are inherent properties of the hydrophilic surface or artifacts of the reversion process is a matter for future testing. | |
