**5. Conclusion**

Photovoltaic and photothermal systems are considered the two main solar cell design technologies, and their design key points are introduced in this chapter. The efficiency and the operating bandwidth are important factors for evaluating the performance of solar cells. To reach efficient solar cells, it is required to optimize the surface geometry in terms of shape, material, and the number of layers. In general,

*Photovoltaic and Photothermal Solar Cell Design Principles: Efficiency/Bandwidth… DOI: http://dx.doi.org/10.5772/intechopen.110093*

#### **Figure 9.**

*Entire solar spectrum absorption coverage with (a) graphene-based nano-pillar absorber and (b) its reflection, transmission, and absorption spectra. (c and d) The sensitivity of the absorption rate to the incident angle respectively for the TE and TM waves [1].*

dielectric materials lead to better performance in comparison to noble metals. To design broadband absorbers, multilayered or multiresonance configurations are proposed. Alternatively, pyramidal/conical geometries, supporting gradual impedance matching with the free space intrinsic impedance, can be exploited. In these geometries, the tip truncation and use of hollow cores improve the low-frequency efficiency. Moreover, environmentally friendly and heat-tolerant materials are the best choice for practical solar cell designs and different types of two-dimensional materials can also be beneficial for solar cell performance optimization. Considering all the factors, novel solar cells with improved performance can be proposed for future applications.
