(377c) Polymer-Nanocrystal Hybrid Solar Cells Using P3HT and Pyrite FeS2

Polymer-Nanocrystal
Hybrid Solar Cells Using P3HT and Pyrite FeS₂

Beau
Richardson, John Bae, Leize Zhu, and Qiuming Yu

Department
of Chemical Engineering, University of Washington, Seattle, WA 98195

qyu@uw.edu

In order to reduce
dependence on exhaustible energy sources and reduce carbon emissions, much
scientific effort has been directed towards reducing the cost of renewable
energy sources to make them competitive with conventional sources.  Solar cells
have great potential as a low-carbon, sustainable energy source but are still
too expensive to compete.  Searching for new materials to design low-cost and
more efficient solar cells can reduce the cost per kilowatt-hour (kWh) of
energy produced from these devices and bring them closer to grid parity.  Specifically,
pyrite FeS₂ nanocrystals have several advantages for making solar
cells but its use in thin-film, bulk-heterojunction type devices has not been
thoroughly studied.

Recently, our group
has demonstrated controllable synthesis of pyrite nanocrystals in octahedral
and cubic shapes.  We are incorporating these nanocrystals into a hybrid, bulk
heterojunction device with the semiconducting polymer Poly (3-hexylthiophene-2,5-diyl)
(P3HT) and studying how the different nanocrystal sizes and
shapes affect charge transport, light absorption, and overall device
performance.  In conjunction with the fabrication of these hybrid devices, we
are also fabricating organic devices with P3HT:PCBM active layers under the
same conditions for direct comparison.  The typical device is fabricated on an
ITO coated glass substrate with a ~40 nm PEDOT:PSS hole conducting layer,
followed by a ~100-200 nm P3HT/pyrite active layer and an ~85 nm Al electrode. The
film thickness and the surface morphology of the hybrid thin films are measured
by AFM. The optical properties of the film are studied using ellipsometry and
UV-vis-NIR absorption spectroscopy.  The power conversion efficiency (PCE) is
determined by measuring the I_sc and V_oc under AM 1.5
Global Spectrum at 100 mW/cm².  A time-correlated single photon
counting (TCSPC) system is used to analyze the relaxation of electrons in these
films from an excited state to a lower energy state.  By employing TCSPC to
study P3HT, pyrite nanocrystals, PCBM, P3HT:PCBM, and hybrid P3HT:pyrite
nanocrystal films, we can elucidate the charge transport characteristics
between the n- and p-type materials.  The effects of the ratio of P3HT:pyrite
nanocrystals, solvent, film thickness and annealing conditions on the device
performance will be discussed.