**4. Conclusions**

*Solar Cells - Theory, Materials and Recent Advances*

substrate [24].

an inorganic part out of e.g. semiconducting nanocrystals [23]. A large number of various semiconductors have been investigated for organic–inorganic hybrid solar cells. For example, titanium dioxide (TiO2) nanoparticles have been extensively employed due to their high power conversion efficiency. Also, Zinc sulfide (ZnS) is another promising semiconductor, but it has been less studied. A top metal electrode (e.g. Al, LiF/Al, Ca/Al) is vacuum deposited onto the photoactive layer finally. **Figure 5** is a schematic illustration of a typical device structure. For photoactive layers there are two different structure types, the bilayer structure and the bulk heterojunction structure. The bulk heterojunction structure is usually realized by just blending the donor and acceptor materials and depositing the blend on a

The charge separation process at the donor- acceptor interface in a hybrid solar cell is shown in **Figure 6**. The major photovoltaic steps include: photo-excitation

*A schematic illustration of typical device structures for hybrid solar cells [24].*

*A schematic diagram of the charge separation process at the donor-acceptor interface in a hybrid solar cell [25].*

**418**

**Figure 6.**

**Figure 5.**

Nano-science is defined as the study of small dimensions materials that exhibit remarkable properties, functionality and phenomena.

Nanotechnology controls current progress in chemistry, physics, material science, biotechnology and electronics to create novel materials that have unique properties because their structures are determined on the nanometer scale [26]. The world needs to curb CO2 emissions soon and reduce our dependence on expensive hydrocarbons; thus, a renewable materials and solar energy on a massive scale are required. Therefore, flexible photovoltaic modules will be among the main tools used to get rid of this dependency.

This chapter has highlighted the advancements that have been made for the fabrication of flexible solar cell and the progress in this field, aimed at facilitating diffusion of these technologies [2].
