**Abstract**

There is a growing interest in recent years on developing solar cells and increasing their conversion efficiency. This interest was motivated by the demand on producing clean and inexpensive energy, where the current solar cell technology failed to fulfill the market demand due to its low efficiency obtained. Thus, an efficient alternative is highly required to overcome the drawbacks of current photovoltaic technologies. In this chapter, the concept and operation of solar rectennas will be introduced as an efficient energy-harvesting technology and as a better alternative to conventional solar cells. Nanoantennas are used for receiving solar radiation at both visible and infrared regions as AC electromagnetic signals. The received power is then passed to a nanodiode that acts as a rectifier to convert the power from AC to DC form. Nanoarrays are utilized often to increase the captured energy and decrease the number of rectifiers of the entire system. The biggest challenge is how to design an efficient nanoantenna integrated efficiently into a nanodiode in order to maximize the overall efficiency. State-of-the-art designs for nanoantennas and nanodiodes will be highlighted in this chapter mentioning the figure of merits used to compare between one design and another.

**Keywords:** energy harvesting, solar rectennas, nanoantennas, nanorectifiers, THz detection
