When studying a new electrochemical couple, numerous variables affect how it is evaluated, how successful it is judged to be, and system properties. In the energy storage field, many researchers evaluate materials using performance metrics that might include capacity, rate capability, or cell impedance values to assess various cell chemistries. Behind these numbers are underlying attributes such as particle morphology, tap density, particle size, surface functionality, and even growth facet that are influenced by the method synthesis. These characteristics can carry through to the final product as the material is transformed into an electrode, high-surface-area catalyst support, or a stand-alone sintered ceramic. In this article, the focus will be on, at a high level, how the synthesis procedure chosen and the variables that come with that choice influence the observed properties of the final product.
. Thin (5-80nm) layers of p-type semiconducting NiO films have been synthesized in a collaboration between the Chang and Marks groups using pulsed laser deposition. These films have been used as hole-transporting/electron-blocking interfacial layers in bulk-heterojunction solar cells of the type [ITO/NiO/P3HT:PCBM/LiF/Al]. The NiO film is polycrystalline in nature and is significantly planarized by the deposition process on the glass/ITO surface with a measured RMS roughness of 1-1.5 nm. The optimal NiO interlayer thickness for the solar cell was found to be 5-10 nm, where an 80% increase in power conversion efficiency (to 5.2%) versus the control was observed. The external quantum efficiency (EQE) was measured on a device containing a 10nm NiO layer and was found to reach a maximum of 87% between 400 and 700 nm. These results highlight the importance of suppressing cell losses, and their adverse effects on power conversion efficiency. The highest power conversion efficiency measured on these cells was 5.2%, and was confirmed by NREL.Surface dipole modifications in In 2 O 3 -based TCOs. In a three-way collaboration between the Mason group (ceramic target synthesis), the Chang group (pulsed-laser deposition), and the Klein group at the Technical University of Darmstadt (RF
The Northwestern University (NU) group combines expertise in first-principles electronic structure theory, exploratory synthesis, thin-film deposition, device fabrication, and characterization. Building on success at NU in developing improved organic light-emitting diodes, the program addressed two crucial aspects of organic photovoltaic (OPV) technology: 1) improved electrode-organic interfaces, and 2) improved transparent electrode materials. The NU group has extensive expertise in the area of unconventional transparent electrodes (or transparent conducting oxides, TCOs), including novel "nanostructured" TCO morphologies. The electronic properties of TCO surfaces (e.g., band offsets/work functions) are believed to play a crucial role in OPV performance. New TCOs were examined that better match (chemically and electronically) the organic components of OPV cells. The group also developed high-efficiency organic adhesion/current-collection layers for improved electrode-organic interfaces. The ultimate goal was to develop and test a high-efficiency prototype organic solar cell incorporating NU-developed interfacial and electrode materials.
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