**6.1 PV cell/generator**

The term PV refers to electricity generators consisting of two semiconducting layers principally used in the construction of the PV cells. The negative layer of the

*Photovoltaic power potential in Pakistan is taken from the global solar atlas.*

#### *Agrovoltaic and Smart Irrigation: Pakistan Perspective DOI: http://dx.doi.org/10.5772/intechopen.106973*

PV cell releases electrons under sunlight. If an external circuit is present, the free electrons move to the positive layer and create an electrical current. So far, the PV cell material science has led toward the 4th generation (4G) PV modules as described in **Figure 10**. The 1G PV cells are thick monocrystalline and multi-crystalline silicon films, which not only leads to highly efficient but also expensive. The efficiency of the thick monocrystalline and multi-crystalline PV cell materials was reported at 26.3% and 21.3%, respectively [58]. The 2G PV cells are synthesized from thin amorphous silicon or polycrystalline Si (silicon), CIGS (copper-indium-gallium-selenium), and CdTe (cadmium telluride) aimed to minimize the cost by employing thin film materials. In comparison to 1G, the performance of the 2G filmed PV cells are inadequate thereby lowering the efficiency. For instance, the thin film chalcogenide such as CdTe has an efficiency range between 19.5% and 21% whereas, in the case of CIGS (minimodule) the efficiency further drops to 18% [59]. In the case of amorphous silicon, the efficiency declined to 10.2% [58]. In this context, a larger surface area will be required to produce electricity equivalent to 1G PV cells. However, the 2G PV cells dramatically reduced the unit cost of electricity generation, which was the key achievement. The 1G and 2G PV modules are highly penetrated in the solar markets having 85% of the market share [60, 61]. The 3G PV modules use nanocrystalline films staked with multilayers of inorganics based on III-V materials such as Gallium arsenide (GaAs), Germanium (Ge), and gallium indium phosphide (GaInP) aimed to improve the efficiency of the system with significantly low production cost [62]. The efficiency of GaAs and GaInP was reported at 37.9% [58]. Despite the acceptable success of 3G cells, major improvements in device performance are necessary if this technology is to compete in terms of cost per watt with prior PV generations. The 4G PV cells introduced the polymers aimed to improve the optoelectronic properties and

#### **Figure 10.**

*Timeline of photovoltaic device generations, from 1G to 4G, with nanomaterial components that make up half of 4G devices [57].*

low-cost thin PV panels/modules. Solar cells having several p-n junctions constructed of various semiconductor materials are known as multi-junction (MJ), which has been widely investigated in the literature. In reaction to different wavelengths of light, the p-n junction of each material will create an electric current. In this case, the cell efficiency was reported beyond 45%. **Figure 11** presents the temporal improvement of the cell efficiency developed by the National Renewable Energy Laboratory, Golden, Co.
