Hybrid Solar Cells with Polymer and Inorganic Nanocrystals - Organic Solar Cells: Materials and Device Physics - page 254

Fig. 9.14 SEM images of
the vertically aligned ZnO
nanorods. Reproduced with
permission from Ref. [ 91 ]
arrays [ 88 ], higher efficiencies could be achieved by infiltrating the blend of P3HT
and PCBM into the ZnO nanorods array [ 98 , 99 ], but the reported efficiencies were
still lower than that of state-of-the-art BHJ organic solar cells.
Besides the above mentioned materials, Si [ 100 , 101 ], InP [ 102 ] and CuO [ 103 ]
nanowire arrays were also used for fabricating hybrid solar cells with conjugated
polymers with the efficiencies normally lower than 2 %.
9.4 Interface Modification for Enhanced Photovoltaic
Performance
There are two important interfaces in HSCs, i.e., the polymer/inorganic nanocrystal
interface where the charge separation takes place and the active layer/electrode
interface where the free charges are collected. Therefore, their properties are crucial
to the device performance. Efficient interface modification could not only facilitate
the charge transport but also retard the backward recombination and remarkably
improve the conversion efficiencies of the solar cells [ 61 , 62 , 65 , 104 - 119 ].
One of the most important work on interface modification was reported by Goh
et al. in 2007 [ 105 ], who systematically studied the effect of interface modification
in TiO 2 /P3HT-based HSCs using different types of modifiers as shown in
Fig. 9.15 , and the corresponding device physics was also provided by the authors.
They concluded that there were two kinds of dipoles existed at the TiO 2 /P3HT
interface when the interface modifiers were introduced; namely, the molecular
dipole and the interfacial dipole that generated by the interaction between the
carboxylic group and TiO 2 . They both could lead to the TiO 2 band edge shift, and
thus affect the V oc of the device. A nearly 2-fold improvement of the PCE was
achieved by using Ruthenium dye which could mediate the interface charge
transfer and slow down the recombination kinetics.