Anomalous Photovoltaic Effect

APE or anomalous photovoltaic effect refers to the photovoltaic effect in specific semiconductors and even insulators. The word “anomalous” here refers to the cases where the photovoltage remains larger than the bandgap that persists between the corresponding semiconductor. 

Here, photovoltage refers to the open-circuit voltage caused by the light. As a result, you can witness the photovoltaic effect in semiconductors. Sometimes, the voltage might even reach thousands of volts. Therefore, the voltage remains unusually high in this regard. 

However, the short-circuit current remains pretty low no matter how high. So, overall, the materials that can exhibit such anomalous photovoltaic effects will have unusually low power generation efficiencies. And so, they are never used in any sort of practical power-generation systems.

So, where do these APEs arise? You can find them in polycrystalline materials, ferroelectric materials, single crystals with non-centrosymmetric structures, etc.

What is the photovoltaic effect?

The photovoltaic effect in semiconductors is defined as the effect that occurs due to the conversion of light energy into electrical energy in semiconductors and insulators. Without involving any intermediate process, it directly converts light energy into electricity.

Let’s talk about a block of silicon crystals to understand this phenomenon properly. Assume that the upper portion of the block is doped with the donor impurities. On the other hand, its lower part is doped with acceptor impurities. Therefore, the concentration of the free electrons seems to be higher in the n-type region than in the p-type region. Also, the concentration of holes is relatively higher in the case of the p-type region than in the n-type region of the block. 

So, comparing these two conditions, you can see a high concentration gradient of charge carriers across the block’s junction line. As a result, the free electrons from the n-type region will eventually diffuse to the p-type region, while the holes in the p-type region will diffuse back to the n-type region within the crystal.

Why does this happen? It occurs due to the charge carriers, who will always try to diffuse from higher concentration to lower region by nature. As a result, each of the free electrons of the n-type region will diffuse into the p-type region and vice versa. So, by forming positive and negative charges, the ions move across the areas, depending on the charge types. 

Understanding photovoltaic effect in semiconductors

Concerning the previous example, understand that positive and negative charges create junctions that give rise to an electric field. As a result of the electric fields, the electrons start moving towards the positive side or p-side while the holes move towards the negative or n-side. 

The electric field thereby causes the movement of charges in one direction, either positive or negative terminal. You already know that light comes from the sun and hence is composed of electromagnetic radiation energy. 

Photons are the primary constituent of light which, when they hit the photovoltaic cell surface, will get absorbed to transfer their energy into the cells. In layman’s terms, the photons will convert the energy stored in them to the electrons present in the semiconductors. As a result, these electrons will get highly excited and start jumping to their next higher energy level, also called the conduction band. 

Once these electrons get active due to energy absorption, they leave behind the holes within the valence band. As a result, it causes a steady movement of these electrons, giving rise to energy to make the two charge carriers move around the electron-hole pair. 

After this, the electrons will show motion in the excited state which causes energy formation leading to the photoelectric effects within the solar panels. Finally, it converts the solar rays from the solar cell into electricity using the chief principle of the photovoltaic effect on solar cells and panels. 

Conclusion 

That is the basic principle of how these solar cells or photovoltaic effects work within semiconductors. It is a widely prevalent practice known for generating clean electricity in the environment. Therefore, future generations can utilise this concept appropriately to produce highly energy-efficient electricity.  

The experts say the sun will last more than 1 billion years. So, utilising photons to generate electricity ethically can be the ultimate solution to global warming and the loss of non-renewable energy resources.