Hierarchical Nanostructures for Solar Cells - Hierarchical Nanostructures for Energy Devices - page 79

randomly distributed within the material, controlling the order-disorder
pore structure (Figure 4.11) 25 allows the opening of a new set of properties
and material performances, especially when pore order is controlled at the
nanoscale. 26 The key issue for the synthesis of porous materials is how to
template the pores, and how to order and shape them. Several strategies
have been proposed to produce porous materials via templates, which are
removed after the material processing, or controlled phase separation. 27 A
templating strategy is also at the base of self-assembly through evapor-
ation, which allows the preparation of mesopores with an ordered and
controlled organization via a combination of sol-gel and supramolecular
chemistry. This process can be combined with other strategies to obtain
hierarchical porous materials that exhibit organization at least in one
length scale. Nakanishi et al. 28 and Huesing et al. 29 have synthesized hybrid
organic-inorganic monoliths with continuous macropores formed by
phase separation along with micro- and mesopores which are templated by
micelles formed by an amphiphilic triblock copolymer. More recently, the
formation of an organic polymer simultaneous to self-assembly has also
been developed as a synthesis route toward macroporous-mesoporous
monoliths. 30 The fabrication of hierarchical porous materials has also been
extended to obtain films with different pore length scales. 31 Controlling the
pore properties is, however, more dicult to achieve in films because the

d n 3 r 4 n g | 9

.

Figure 4.11 Illustration of the main synthesis and fabrication routes that have been

used to obtain hierarchical porous films by combining self-assembly
with other templating strategies. 25
Reproduced with permission from ref. 25.