Polymer morphology and aggregation play an essential role for efficient charge carrier transport and charge separation in polymer-based electronic devices. It is a common method to apply the H-aggregate model to UV/Vis or photoluminescence spectra in order to analyze polymer aggregation. In this work we present strategies to obtain reliable and conclusive information on polymer aggregation and morphology based on the application of an H-aggregate analysis on UV/Vis and photoluminescence spectra. We demonstrate, with P3HT as model system, that thickness dependent reflection behavior can lead to misinterpretation of UV/Vis spectra within the H-aggregate model. Values for the exciton bandwidth can deviate by a factor of two for polymer thicknesses below 150 nm. In contrast, photoluminescence spectra are found to be a reliable basis for characterization of polymer aggregation due to their weaker dependence on the wavelength dependent refractive index of the polymer. We demonstrate this by studying the influence of surface characteristics on polymer aggregation for spin-coated thin-films that are commonly used in organic and hybrid solar cells.

Arrays of silver nanowires have received increasing attention in a variety of applications such as surface-enhanced Raman scattering (SERS), plasmonic biosensing and electrode for photoelectric devices. However, until now, large scale fabrication of device-suitable silver nanowire arrays on supporting substrates has seen very limited success. Here we show the synthesis of free-standing silver nanowire arrays on indium-tin oxide (ITO) coated glass by pulsed electrodeposition into anodic aluminum oxide (AAO) templates. We use an in situ oxygen plasma cleaning process and a sputtered Ti layer to enhance the adhesion between the template and ITO glass. An ultrathin gold layer (2 nm) is deposited as a nucleation layer for the electrodeposition of silver. An unprecedented high level of uniformity and control of the nanowire diameter, spacing and length has been achieved. In photovoltaics nanowire arrays are of particular interest for costeffective organic and hybrid solar cells, whose near-optimal architecture is proposed to consist of arrays of nanostructures (approximately 200 nm long).12,13 The major advantage to using nanowire arrays is the enhancement of the charge collection due to the high charge carrier mobility in the metallic and some semiconductor nanowires. 13,14 However, due to the huge junction area, most semiconductor nanowire solar cells face limitations in device performance due to charge recombination across material interfaces, 13,14 leading to poor solar cell performance. Many research groups have tried to address this issue by developing metal oxide core-shell nanowire arrays. [15][16][17] In this work, a conductive metal oxide core (e.g. ZnO) is coated with a shell layer with an offset conduction band (e.g. TiO 2 , Al 2 O 3 ) in order to further increase distance between electron-hole pairs while simultaneously promoting charge extraction along the axis of the nanowire. This phenomenon was further employed in doped TiO 2 core-shell wires to amplify the electron mobility in the core of the wire without forming a recombination center along the internal interface.18 However, to ultimately enhance the performance of organic solar cells, a hybrid core-shell nanostructure with enhanced charge mobilities could provide an optimal electrode, e.g. a Ag nanowire with an inorganic shell layer. Additionally, these wires promote field amplification via plasmonic resonance as well as acting as a light scatterer, 19 leading to an increase in absorption in the surrounding active layers of the organic solar cells.For our approach, we use an industrially-applicable method for producing silver nanowires on a large area via filling anodic aluminum oxide (AAO) templates using electrodeposition. AAO was first introduced as a self-organizing mesoporous structure by Keller et al. in 1953. 20 Much research was later conducted to improve the formation and to fabricate AAO pores with various pore distances and diameters using thick (∼ mm) bulk Al foils. 21 Recently, it has been shown that the production of AAO templates ...

An electrode structured with a TiO2/Ag/TiO2 (TAT) multilayer as indium tin oxide (ITO) replacement with a superior thermal stability has been successfully fabricated. This electrode allows to directly tune the optical cavity mode towards maximized photocurrent generation by varying the thickness of the layers in the sandwich structure. This enables tailored optimization of the transparent electrode for different organic thin film photovoltaics without alteration of their electro-optical properties. Organic photovoltaic featuring our TAT multilayer shows an improvement of ∼12% over the ITO reference and allows power conversion efficiencies (PCEs) up to 8.7% in PTB7:PC71BM devices.

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