Hybrid Solar Cells with Polymer and Inorganic Nanocrystals - Organic Solar Cells: Materials and Device Physics - page 246

Fig. 9.4 Molecule structures
of the four common used
conjugated polymers in
hybrid solar cells
micromorphologies, i.e., nanoparticles, nanorods and nanorod-, nanowire-, and
nanowire arrays. The micromorphologies of inorganic nanocrystals may have pro-
found effect on the performance of HSCs [ 9 , 48 ].
9.3.1 Nanoparticles
The charge separation and transport in the conjugated polymer/semiconductor
nanocrystals composites were first studied by Greenham et al. in 1996 [ 8 ]. A HSC
with ITO/MEH:PPV-CdSe/Al structure was fabricated, after incorporating 90 wt%
of CdSe into the polymer matrix the device gave a 0.6 % PCE and a 12 %
quantum efficiency at 514 nm, while the PCE could only approached 0.1 % under
80 mW/cm 2 white light. After the breakthrough in control the shape of CdSe
nanocrystals, CdSe quantum dots (QDs), nanorods, and tetrapods have been
extensively studied [ 49 - 51 ]. Compared to the earlier CdSe QDs based HSCs, the
PCEs have been improved by an order of magnitude, through the modification of
CdSe QDs and the use of new polymers [ 52 - 54 ], however, the elongated CdSe
nanocrystals were found to have better charge transport properties than nanopar-
ticles, consequently drew more attention [ 9 , 10 , 12 , 48 ].
Triggered by the research on CdSe nanocrystals, charge transport properties in
TiO 2 /polymer heterojunction were also studied and photoinduced charger transfer
from conjugated polymers to TiO 2 was confirmed to be possible [ 55 - 57 ]. Mesoporous
TiO 2 film with a uniform pore distribution was prepared with the block polymer
template (Fig. 9.5 ) and used for preparing HSCs by infiltrating P3HT into the pores, a
monochromatic PCE of 1.5 % was obtained at 33 mW/cm 2 514 nm illumination and
an efficiency of 0.45 % was estimated under AM 1.5 condition [ 16 , 17 ]. Besides, many