Hybrid Solar Cells with Polymer and Inorganic Nanocrystals - Organic Solar Cells: Materials and Device Physics - page 252

Fig. 9.11 Tilted SEM cross-section images of the CdSe nanorod/P3HT solar cells with different

nanorod lengths: a nanorod free, b 58 ± 12 nm, c 280 ± 85 nm, d 368 ± 41 nm,

e 612 ± 46 nm, f 721 ± 15 nm. Reproduced with permission from Ref. [ 85 ]

based on CdTe nanorod array and poly(3-octylthiophene) (P3OT), then the MEH-
PPV/CdS nanorod array device was fabricated with an efficiency of about 0.6 %
[ 13 ]. Schierhorn et al. [ 84 ] successfully synthesized vertically aligned CdSe
nanorods on ITO glass and systematically investigated the influence of nanorod
length on the device performance (see Fig. 9.11 ), As shown in Fig. 9.12 , the J sc
increased linearly with nanorod length and the device based on 612 ± 46 nm long
nanorod gave the highest efficiency of 1.38 % [ 85 ].
Shankar et al. [ 86 ] demonstrated a single heterojunction solid-state solar cell by
sensitizing the anodic TiO 2 nanotube array with a P3HT derivative. However, the
device exhibited poor performance due to the bad contact between the active layer
and electrode. When they infiltrated both P3HT and PCBM into TiO 2 nanotube
arrays to form double heterojunction solar cells, a 1 % PCE was achieved.
Vertically aligned TiO 2 nanorods were used to fabricate HSC with P3HT by Kuo
et al. [ 87 ], but only a 0.12 % PCE was obtained. Higher efficiency could be
realized by the control of the dimensions of the nanorods and/or sizes of the D/A
domains. Tepavcevic et al. [ 88 ] found that, when the polymer was in situ poly-
merized in the TiO 2 nanotube arrays, the device showed a much stronger ([10 3 )
photocurrent density than that of device fabricated with ex-situ synthesized
polymer. However, the white light efficiency was not reported by the authors. Mor
et al. [ 89 ] successfully demonstrated an efficient TiO 2 nanotube arrays/dye/P3HT
device structure (see Fig. 9.13 ), where the dye accounted for the absorption of the
red and near-infrared portion of the solar spectrum while P3HT absorbed
the higher energy photons and served as a hole transport material. Such a device
that combined the advantages of both solid-state DSSC and BHJ solar cell showed
an average PCE as high as 3.2 %. Recently, highly oriented TiO 2 nanotubes were
synthesized with ZnO nanorod template and a 3.32 % efficiency was reported for
the HSC fabricated by infiltrating P3HT/PCBM into the TiO 2 matrix [ 90 ].
Vertically aligned ZnO nanorods and nanowires that could be easily prepared
were also extensively studied for preparing high performance HSCs. Figure 9.14
presents the typical morphology of ZnO nanorods array. The charge recombination