Photovoltaic & Optoelectronic Device Group

Abstract:

A new self-assembly platform for the fast and straightforward synthesis of bicontinuous, mesoporous TiO 2 films is presented, based on the triblock terpolymer poly(isoprene-b-styrene-b-ethylene oxide). This new materials route allows the co-assembly of the metal oxide as a fully interconnected minority phase, which results in a highly porous photoanode with strong advantages over the state-of-the-art nanoparticle-based photoanodes employed in solid-state dye-sensitized solar cells. Devices fabricated through this triblock terpolymer route exhibit a high availability of sub-bandgap states distributed in a narrow and low enough energy band, which maximizes photoinduced charge generation from a state-of-the-art organic dye, C220. As a consequence, the co-assembled mesoporous metal oxide system outperformed the conventional nanoparticle-based electrodes fabricated and tested under the same conditions, exhibiting solar power-conversion efficiencies of over 5%. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

Energy relay dyes (ERD) and Förster resonant energy transfer (FRET) are useful techniques for increasing absorption in dye-sensitized solar cells. We use femtosecond transient absorption spectroscopy to monitor charge generation processes in a solid-state DSC containing poly(3-hexylthiophene) (P3HT) as both the hole-transporter and the ERD with a zinc phthalocyanine dye (TT1) as the sensitizer. We observe efficient FRET occurring on picosecond time scales and subsequent hole transfer from TT1 to P3HT occurring onward from 100 ps.

Abstract:

Morphology control on the 10 nm length scale in mesoporous TiO(2) films is crucial for the manufacture of high-performance dye-sensitized solar cells. While the combination of block-copolymer self-assembly with sol-gel chemistry yields good results for very thin films, the shrinkage during the film manufacture typically prevents the build-up of sufficiently thick layers to enable optimum solar cell operation. Here, a study on the temporal evolution of block-copolymer-directed mesoporous TiO(2) films during annealing and calcination is presented. The in-situ investigation of the shrinkage process enables the establishment of a simple and fast protocol for the fabrication of thicker films. When used as photoanodes in solid-state dye-sensitized solar cells, the mesoporous networks exhibit significantly enhanced transport and collection rates compared to the state-of-the-art nanoparticle-based devices. As a consequence of the increased film thickness, power conversion efficiencies above 4% are reached.

Abstract:

The research field of photovoltaics is booming due to the recognised imperative to realise a long term solutions to clean and inexpensive power generation. With this rapid growth in activity, new concepts and new directions, it is becoming more and more important to be able to effectively compare technological advances made in different research groups, and between the different competing technologies. In this article it is illustrated how challenging it can be to fairly asses the efficiency of a solar cell. Specific examples of how much of an influence a range of measurement practices can have on the estimated short-circuit photocurrents and efficiencies are shown for a number of the most commonly researched excitonic solar cell concepts. In the worst case scenario, systematic overestimations by a factor of 5 can be made. For completeness, the influence of the light source, and the correct method to properly calibrate a solar simulator and estimate the spectral mismatch factor is also described. The error in calibrating the light source is actually likely to lead to a much smaller variance than the definition of the active area of the solar cell. The undeniable implication is that it is essential for excitonic solar cells to be correctly masked to define the active area, if the measured efficiency is to bear a true resemblance of the device performance. Adoption of standard protocols across the field will enable a much better comparison between literature values of efficiency and more rapid and well directed technological advancement will occur. © 2012 The Royal Society of Chemistry.