The infiltration of dissolved dyes into vertically aligned carbon nanotube arrays (va-CNT) is reported. The ultra hydrophobic surface of the CNT forest can be wetted and hence infiltrated for an appropriate choice of solvent. The dye-infiltrated CNT array forms a well ordered bulk-heterojunction structure for organic solar cells in which the CNT can act as a large electrode or, for appropriate energy levels, as an acceptor material. Derivatives of the small molecule copper phthalocyanine or the polymer poly(3-hexylthiophene) were used as dyes. Drop coating was chosen as the infiltration technique resulting in a completely embedded CNT forest. Field emission secondary electron microscopy analysis illustrates the final layer quality. Common electrical characterization under AM1.5 illumination proves photosensitivity and implies photovoltaic behavior of the composite.

The first Electrolyte-less dye sensitized solar cell (ELDSC) is proposed with the architecture of FTO-TiO2-dye-metal. In the ELDSC design, the most significant contact is the TiO2-dye-metal interface, whereby the metal electrode acts as the charge replenishment layer as well as the external electrode. In previous work, ELDSC has an inferior Fill Factor (FF) due to insufficient metal coverage from top-down physical vapor deposition. In this work, a three dimensional (3D) metal network plated through the mesoporous TiO2 network is achieved through bottom-up metal electroplating. This study focuses on the characteristics of electro deposition onto insulating planar TiO2 as well as mesoporous TiO2 network. For planar TiO2, gold (Au) islands form readily, becoming worm-like structures as they coalesce, subsequently becoming a continuous layer. (The plated metal on the insulating TiO2 layer is made possible by plane defects within the insulator layer that serve as the conductive supply path.) In contrast, electroplating carried out on a FTO-planar TiO2-mesoporous TiO2 substrate results in a 3D Au network within the mesoporous TiO2, where Au cords were observed as the connections among Au islands. This study demonstrates that a continuous metal layer can be electroplated onto an insulating TiO2 layer, borrowing its intrinsic planar defect network. Further, applying the same principle, a 3D metal network can be formed within mesoporous TiO2.

The effect of an external electric field during post-annealing on the device characteristics of poly(3-hexylthiophene) (P3HT) and phenyl-C61butyric acid methyl ester (PCBM) bulk heterojunction solar cells was studied. The application of external electric field in forward bias resulted in significant enhancement in Voc and fill factor whereas devices annealed under reverse bias had an enhanced Jsc. Both forward and reverse bias annealing increased the shunt resistance. The Al - blend interface topography and carrier dynamics were studied using conducting atomic force microscopy and frequency dependent intensity modulated photocurrent spectroscopy (IMPS). The results indicate that post-annealing under external electric field can be used to engineer the interface composition to enhance the charge transport in bulk heterojunction solar cells to improve the device performance.

The commercial viability of solar power will depend on a careful balance of reliability, efficiency, and overall cost. A systematic approach to the optimization of the latter two for the case of organic solar cells is outlined. This relies among other on the development of a detailed understanding of the charge generation process and the systematic application of analytical tools such as UV-vis, photoluminescence, lifetime measurements, and current-voltage (I-V) curves.

This article describes design of fullerene-based electron-accepting materials to obtain high performance in organic thin-film photovoltaic devices. A 1,4-bis(dimethylphenylsilylmethyl)[60]fullerene gives higher open circuit voltage than 1,2-diadduct because of smaller π-conjugated systems, and enables columnar fullerene-core array for high electron mobility and thermal crystallization for ideal phase separation with electron-donor materials. A 56π-electron fullerene derivative possessing the dihydromethano group as the smallest carbon addend does not disrupt fullerene-fullerene contact in solid state, giving high open-circuit voltage without decreasing of short-circuit current density and fill factor.

For inorganic semiconductor solar cells, controlled doping is important because it can cause Fermi level shift of the inorganic semiconductor and achieve ohmic contact at the metal-semiconductor interface. In this paper we show that doping can also be used to shift Fermi level in organic semiconductors and cause changes in solar cell performance. We have made chloroindium phthalocyanine (ClInPc)/C60 heterojunction solar cells, where tetrafluoro-teracyano-quinodimethane (F4-TCNQ) is used to dope ClInPc layer. Ultraviolet photoemission spectroscopy (UPS) is used to investigate the ITO/ClInPc interfaces. The result shows that doping causes a Fermi level shift at the ITO/ClInPc interface as it does for inorganic semiconductors. As the doping increases, dark saturation current J0 of the solar cell increases, while open-circuit voltage Voc, short-circuit current Jsc and fill factor decreases. As a result, the efficiency of the solar cell decreases as doping increases. More UPS studies on ClInPc (doped with F4TCNQ)/C60 junction are needed to correlate the energy band diagram of the whole solar cell structure with the J-V characteristics.

We present the development of highly efficient merocyanine solar cells at the example of the dye MD376. Due to their unique processing flexibility, merocyanines have been applied in solution- as well as vacuum-processed organic photovoltaics. In fully vapor-deposited MD376 single cells, efficiencies up to 5.0% were achieved while maintaining a rather simple device setup with only four organic layers. Moreover, MD376 has been successfully introduced to vacuum-processed tandem cell structures, reporting a high open-circuit voltage of 2.1 V.