The anchoring mechanism of N719 dye molecules on oxalic acid treated TiO 2 (OA-TiO 2) electrodes has been investigated using extended X-ray absorption fine structure (EXAFS) measurements, Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The FTIR spectroscopy of OA-TiO 2 electrodes revealed that the oxalic acid dissociates at the TiO 2 surface and binds through bidentate chelating and/or bidentate bridging. Analyses of EXAFS, FTIR, UV-Vis and XPS measurements of N719 dye loaded onto OA-TiO 2 revealed that the binding of N719 molecules takes place via interaction between Ru atom of the dye and Oof bidentate bridged oxalate ions at TiO 2 surface. This mechanism is quite different to the binding of N719 onto untreated TiO 2 (WO-TiO 2) surface, where-COOH and SCN groups of the dye directly bind to TiO 2 surface. The analyses of UV-Vis data show that the amount of N719 dye loading is much higher onto OA-TiO 2 surface as compared to the native TiO 2 surface. In addition, the incident photon to current conversion efficiency (IPCE) measurements show that presence of oxalate ions between dye and TiO 2 surface favors efficient electron transfer, and therefore, improvement in device efficiency. The dye sensitized solar cells fabricated using N719 dye sensitized onto OA-TiO 2 showed an efficiency of ~4.6%, which is significantly higher than that based on WO-TiO 2 electrode (~3.2%).

Harnessing solar energy with solar cells based on organic materials (in particular polymeric solar cells) is an attractive alternative to silicon-based solar cells due to the advantages of lower weight, flexibility, lower manufacturing costs, easier integration with other products, low environmental impact during manufacturing and operations and short energy payback times. However, even with the latest efficiencies reported up to 17%, the reproducibility of these efficiencies is not up to par, with a significant variation in the efficiencies reported across the literature. Since these devices are based on ultrathin multilayer organic films, interfaces play a major role in their operation and performance. This review gives a concise account of the major interfacial issues that are responsible for influencing the device performance, with emphasis on their physical mechanisms. After an introduction to the basic principles of polymeric solar cells, it briefly discusses charge generation and recombination occurring at the donor-acceptor bulk heterojunction interface. It then discusses interfacial morphology for the active layer and how it affects the performance and stability of these devices. Next, the formation of injection and extraction barriers and their role in the device performance is discussed. Finally, it addresses the most common approaches to change these barriers for improving the solar cell efficiency, including the use of interface dipoles. These issues are interrelated to each other and give a clear and concise understanding of the problem of the underperformance due to interfacial phenomena occurring within the device. This review not only discusses some of the implemented approaches that have been adopted in order to address these problems, but also highlights interfacial issues that are yet to be fully understood in organic solar cells.

No abstract

No abstract

No abstract