(71g) Role of Light Scattering in Hybrid Solar Cells

Hybrid solar cells, with an inorganic/organic interface for charge separation, have been extensively investigated in
the past decade in order to replace the expensive Si based technology with an inexpensive alternative. Typically,
these devices incorporate a mesoporous TiO₂ film which is decorated with dye molecules and filled with a hole
transport material, to conduct the electrons and holes, respectively. Recently, devices with an liquid electrolyte
have been able to reach up to 13% conversion efficiency. However, the TiO₂ mesoporous films used for solid
state dye sensitized solar cells and hybrid solar cells have a limited light absorption due to thickness of the film
(500 nm – 2 µm) required for efficient charge transportation. An elegant approach to increase the light absorption
is to induce “defects” within the mesoporous film, causing light to scatter within the active layer of the device. In
this work, we combine the commonly used 25 nm particles with other nanostructures, including 200 nm TiO2
particles, TiO₂ nanowires, and Sn doped nanowires, all of which produce light scattering due to their dimensions
and  disorder  within  the  active  layer.  Through  this  approach,  we  are  able  to  correlate  an  improvement  in
conversion efficiencies of around 25 % to the light scattering. Furthermore, the incorporation of these nanowire
structures  increases  the  mobility  of  the  electrons,  allowing  for  increased  charge  extraction  and  reduced
recombination. These two phenomena can be simultaneously engineering due to the crystallinity of the “defects”
within the films and the cascading conduction bands produced with the incorporation of the doped TiO₂ wires.
The  extent  of  the  reduction  in  recombination  is  quantified  through  photovoltage  decay  and  impedance
spectroscopy measurements and compared to the standard mesoporous TiO₂ devices.