Time-resolved terahertz spectroscopy of dye-sensitized solar cells

This project is related to the following Fields, Subjects and Techniques:

Motivation

Solar cells based on dye-sensitized nanoparticles are promising due to their high efficiency (up to 10 %) and relatively low fabrication costs. However, their further development requires to understand in detail the basic photo-initiated processes. Here we use time-resolved terahertz (THz) spectroscopy to probe the transport properties of free charge carriers generated upon photo-excitation.

Transient conductivity spectrum of a thin film containing ZnO nanoparticles. The excitation wavelength was 332 nm.

In the graph above, a conductivity spectrum of a photo-excited film with ZnO nanoparticles is shown. Since the energy of excitation photons is higher than band gap of ZnO, free charge carriers are generated. Presence of free charge carriers is demonstrated by the non-zero real part of photo-conductivity at the lowest THz frequencies. However, the increase of the real part with frequency and the negative imaginary part indicates that the nanostructure limits the motion of photo-generated free charge carriers.

We are presently investigating ZnO nanoparticles sensitized by various rigid-rod porphyrins. Chemical structure of one of its representatives is plot below.

Chemical structure of a rigid-rod porphyrin.

Collaborations

• Elena Galoppini at Rutgers University, New Jersey, USA