Photodetectors have a wide role to play in almost all basic electronic project these days. These photodetectors are mostly used for sensing the presence or absence of any object. The photo-based equipment or devices can be classified into three categories – the photovoltaic devices, photoconductive devices, and the photoemission devices. However, in this blog, we will only talk about photovoltaic devices. Moving over to the photovoltaic cells, these are most commonly known as solar cells. Derived from silicon, these have the ability to bring out the voltage in light’s presence. The amount of voltage produced by them mainly depends on the material that is used for making solar cells. A silicon-based solar cell can give you 0.5 volts of potential difference in direct sunlight. When this solar cell is connected with a closed circuit than the flow of current takes place through the circuit. The quantity of current generated by the solar cell is determined by surface areas of the solar cell. 

 

 

 

When you observe a schematic symbol of solar cell it shows the charge difference like a single cell battery along with two arrows. These arrows show that light has fell over the cell for production of voltage. With respect to the real-time applications of the solar cell, there are two facts that need to be kept in mind, one, the silicon-based solar cell generates just 0.5 volts so, you need to add more cells in series to create sufficient voltage. Similarly, for more current, multiple photovoltaic cells need to be connected in parallel. Assume that you need to create a system to turn a relay on or off whenever a place gets more than required brightness. Now imagine that the relay coil needs 3 volts at 250mA to work out. You can use the following circuit pattern to meet the requirement. 

 

In this figure, you need to assume that every single cell has the capability to generate 0.5Volt at 150mA. Since one cell is capable of generating. 5Volts, you will need 6 cells to connect them into a series and obtain 3 volts. For getting the 150mA you will have to connect 6 or more cells in parallel. This is just one example but I hope it will help you understanding the concept.