**2. State of the art on solar cells - introduction on CIGSe-based thin films**

#### **2.1 State of the art in thin film industry**

The photovoltaic market has experienced rapid development since 2003, with a growth rate of 40% until 2009 and 135% in 2010, reaching an installed capacity of 40 GW. This market is dominated by technologies based on crystalline silicon. Developed for 60 years, the silicon industry witnessed many advances. In 2012, it represented 90% of the photovoltaic market share [8]. We can then distinguish two large families of cells depending on the nature of the silicon wafer, monocrystalline (m-Si) or poly crystalline (p-Si), for which the record yields are 26.8% (homo-junction), 24.9% (heterojunction) and 21.7% (homojunction), 20.3% (heterojunction) respectively [9]. Research in this field has been extremely active in recent years and advances have been rapid, which has allowed the advent of photovoltaic technologies that consume less energy and only require a few microns in thickness (compared to around 200 microns for silicon) and costs of smaller productions. This is the so-called second generation thin-film cell industry. Their main advantage comes from the small amount of materials needed to make a cell. This generation experienced a 39% increase in production between 2010 and 2014 and more than 50% between 2015 and 2019. There are mainly three (03) sectors in that field:

• **Amorphous silicon (a-Si) thin films**: they have record efficiencies of around 11% for single junction amorphous silicon cells and 12.6% for tandem double junction amorphous silicon/micro-amorphous silicon cells.

*Thin-Film Solar Cells Performances Optimization: Case of Cu (In, Ga) Se2-ZnS DOI: http://dx.doi.org/10.5772/intechopen.93817*


The third generation includes all the new approaches proposed and developed in recent years, this generation is to reduce manufacturing costs (Organic solar cells, Gräetzel<sup>1</sup> cells, etc.). It seeks to overcome the current limits of yields by resorting to original concepts such as multi-junction cells, intermediate gap cells or using hot carriers. The majority of third generation systems are currently under development and target more or less long-term industrial applications. Gräetzel cells for example can offer a yield of up to 11.5% [1].
