Prof Henry Snaith FRS

Abstract:

The solid-state dye-sensitized solar cell (DSSC) was introduced to overcome inherent manufacturing and instability issues of the electrolyte-based DSSC and progress has been made to deliver high photovoltaic efficiencies at low cost. However, despite 15 years research and development, there still remains no clear demonstration of long-term stability. Here, solid-state DSSCs are subjected to the severe aging conditions of continuous illumination at an elevated temperature. A fast deterioration in performance is observed for devices encapsulated in the absence of oxygen. The photovoltaic performance recovers when re-exposed to air. This reversible behavior is attributed to three related processes: i) the creation of light and oxygen sensitive electronic shunting paths between TiO and the top metal electrode, ii) increased recombination at the TiO/organic interface, and iii) the creation of deep electron traps that reduce the photocurrent. The device deterioration is remedied by the formation of an insulating alumino-silicate shell around the TiO nanocrystals, which reduces interfacial recombination, and the introduction of an insulating mesoporous SiO buffer layer between the top electrode and TiO, which acts as a permanent insulating barrier between the TiO and the metal electrode, preventing shunting. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

We studied charge transport in anodized TiO2 nanotubes in the context of their application in dye-sensitized solar cells. Optical-pump-THz- probe spectroscopy revealed short free carrier lifetimes of about 15-30 ps, which we attribute to shallow trapping. © 2013 IEEE.

Abstract:

In this work we demonstrate hyperbranched nanostructures, grown by pulsed laser deposition, composed of one-dimensional anatase single crystals assembled in arrays of high aspect ratio hierarchical mesostructures. The proposed growth mechanism relies on a two-step process: self-assembly from the gas phase of amorphous TiO2 clusters in a forest of tree-shaped hierarchical mesostructures with high aspect ratio; oriented crystallization of the branches upon thermal treatment. Structural and morphological characteristics can be optimized to achieve both high specific surface area for optimal dye uptake and broadband light scattering thanks to the microscopic feature size. Solid-state dye sensitized solar cells fabricated with arrays of hyperbranched TiO2 nanostructures on FTO-glass sensitized with D102 dye showed a significant 66% increase in efficiency with respect to a reference mesoporous photoanode and reached a maximum efficiency of 3.96% (among the highest reported for this system). This result was achieved mainly thanks to an increase in photogenerated current directly resulting from improved light harvesting efficiency of the hierarchical photoanode. The proposed photoanode overcomes typical limitations of 1D TiO2 nanostructures applied to ss-DSC and emerges as a promising foundation for next-generation high-efficiency solid-state devices comprosed of dyes, polymers, or quantum dots as sensitizers.

Abstract:

We demonstrate the viability of large area processing for solid-state dye-sensitized solar cells. We fabricate mini-modules comprising two photoactive regions connected in series, of 8 cm2 total active area, using the technique of doctor blade coating to deposit the hole-transporter material. For the optimized protocol we lose only 25% of the power conversion efficiency when compared to standard test devices which are only 0.12 cm2. We estimate pore-filling fractions using reflectance spectroscopy, showing that device performance is linked to changes in the volume of the mesoporous TiO 2 photoanode infiltrated with hole-transporter as deposition temperature is varied. © 2013 AIP Publishing LLC.