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Thin film-based second and third generation photovoltaics (PVs) are avidly investigated for their potential for utility scale applications. Organic thin film (PEDOT) and silicon-based PVs are shown to have moderate device efficiency. To further improve efficiency, silicon is sandwiched between thin films of PEDOT and TiO2. Thin films of TiO2 were synthesized at 100 °C and were shown to make efficient (~12%) PEDOT/Si/TiO2-based PVs in which TiO2 functions as a hole-blocker. Lower efficiencies of the PVs than predicted by theory is attributed to poor passivation of the Si/TiO2 interface. To improve the interface passivation, the Si/TiO2 interface is treated under various chemical conditions. Two such treatments yielded very high level of passivation (SRV ~ 15 to 100 cm/s). The well-passivated interfaces are characterized by QSSPCD, XPS, ATR-FTIR and J-V measurements. High resistivity of particular devices was ascribed to the poor conductivity of TiO2. The conductivity of TiO2 is improved by doping with niobium. Niobium is incorporated into the TiO2 lattice from 0.05 to 90 mol%. The doped material is characterized by XRD, XPS, conductivity, magnetization, UV-vis diffuse reflectance and Kelvin probe measurements. Room temperature measurements indicate that Nb-doped TiO2 with only 3 mol% niobium has highest conductivity. Conductivity and work function measurements suggest that Nb-doped TiO2 has the potential to be a conductive hole-blocker for the PEDOT/Si/TiO2 based PV system. Advisors/Committee Members: Schwartz, Jeffrey (advisor), Cava, Robert J (advisor).