One of the best ways to capture Solar Energy is through solar cells.The commercial solar cells of the present times are nothing but photo voltaic cell in an integrated fashion. These are usually semiconductor diodes, generally made out of silicon. As said previously, the process of making the plates highly alter the efficiency of solar panels but also adds a bulk to the cost making it unavailable for commercial use.
When light hits silicon then the electrons are ejected as per Photoelectric Effect. These electrons gain kinetic energy when knocked out by photon allowing them to flow. By adding impurities like Boron and Phosphorous an electric field is developed which develops a diode, allowing electrons to flow in a particular direction, generating a current which are mainly used for charging batteries or supplying power to an electrical appliance.
Drawbacks of conventional Solar Panels
The conventional silicon solar cells have two major Drawbacks. Firstly, the have very low efficiency. Most massed produced solar cells have an average efficiency of 10%. Certain Solar cells can reach efficiency of at most 20%. The main reason of this low efficiency is the because silicon cells can absorb only a particular spectra of frequencies, wasting about 70% of the radiation just for the inability to absorb it. The second one is the high cost of solar cells. For large scale implications in the day to day lives the cost of solar cell must go down. If this is so then many families can cover their houses with solar panels reducing the need for fossil fuels.
Introducing Nano Technology
Many materials show some remarkable properties in 1-100nm scales which is not observed in their scaled up, crude versions. In search scale certain materials have depicted properties like super strength, super conductivity, transparency etc. For example Graphene in its macroscopic form takes the form of a lump of coal or Graphite pencils, but when laid down into a single sheet and it has wonderful properties (High Strength, Optically transparent and Super conducting).
Graphene's scope in Solar Tech.
Due to these awesome properties of graphene, it has awesome scope in various parts of solar panels :-
- As charge carriers:- It has a very low resistances of 3.5 micro ohm/cm^2 and is a 2-D material. If we look at an ordinary Solar panel we notice that its covered by metal strip wires that captures the free electrons knocked down by the sun rays and transport them to generate current. There are two main problems with it. Firstly it is unable to cover all the areas to get electricity due to its second disadvantage, which is it blocks the parts which it covers from getting sun rays. This reduces the efficiency by about 5%. This is where Graphene fits in. It is transparent and can also carry electrons thus increasing efficiency.
- Flexibility :- Graphene is also highly flexible and is thus ideal for organic solar cells which is known for its flexibility. Graphene is indispensable for all those which require both flexibility as well as transparency. Till now Indium 10 Oxide is used to meet Conductive and Transparent requirements of solar cells, but ITO is brittle in nature, so graphene serves as an alternative. Moreover ITO is very expensive unlike Graphene and can cause damage to the organic layer which is sensitive to wear and tear. On the other hand graphene has a more natural bonding to it.
- Photo Voltaic Material:- Mostly all Photo Voltaic cells are based on P-N type semiconductor material, but recently some new breed of PV cells are emerging based on Scottky Junction Diode as an attempt to increase the efficiency. It add an impurity energy level in between the band gaps by using some new materials. One of these new materials is doped Graphene. It has been reported that Graphene Si Scottky cells have reached efficiencies of 10.69% and Graphene Perovskite cells have reached efficiencies of 20.3%.
 |
| Graphene Sheets |
Plastic Solar cells
Plastic solar cells are synthesised using polymers of organics compounds and then dyed with Titanium(4) Oxide. These are also called DSSC or Dye-Synthesised Solar Cell. The process is as follows:-
- The photon hits the C-C double bonds of the organic polymer and ejects an electron. Titanium peroxide nano particles allow a whole range of frequencies and increases efficiency.
- The electron is carried through the nano particles (Dye) and exits the anode.
- Then it moves round the circuit and does work ( Light bulb, Charge Battery etc).
- Goes to the cathode, where it is carried back to the dye by carrier [I(3-) ions].
DSSC are a great alternative to commercial solar cells made out of silicon due to its inexpensiveness and extensive uses. Flexible DSSCs are less efficient but their expensive use and applicability accounts for it. It can even be used to make transparent glasses for windows. These have an efficiency of about 8%.
Nano Wires
Nano wires are microscopic wire that have dimensions of about 40-50 nm. These have some awesome properties. Nano silicon wires when used in making photo voltaic solar cell help increase efficiency when used of a correct length. The key criteria for highly efficient solar cells are a high absorption of incident light in the active region of the carrier collection and minimum loss of carriers due to recombination. The conventional silicon cells have relatively thick diffusion layer as compared to the much thinner drift layer, for carrier collection. Thus to keep a high efficiency(25%) Si solar cells require a very high Quality, defect free plates. Nano wires are easily manufacturable and low in cost. They have reached an efficiency of 3.5% but hopes to achieve at least 70% of the commercial ones but at a much lower cost.
 |
| Black Silicon |
Quantum Dot Solar cell :-
Quantum are subatomic semiconducting particles which are reduced below the size of bound state Bohr Radius (0.529 angstrom). Due to quantum considerations the the electron energies that can exist within them become finite, much alike energies in an atom. Quantum dots are refereed as "Artificial Atoms". These can be prepared in a wide range of sizes and with variety in the bandgap without altering the underlying material. In typical wet chemistry preparations, the tuning is accomplished by varying the synthesis duration or temperature.
The ability to tune the bandgap makes quantum dots attractive candidate for usage in solar cells. For the sun's photon distribution spectrum, the Shockley-Queisser limit indicates that the maximum solar conversion efficiency occurs in a material with a band gap of 1.34 eV. Single junction implementations using lead sulfide (PbS) colloidal quantum dots (CQD) have bandgaps that can be tuned into the far infrared, frequencies that are typically difficult to achieve with traditional solar cells. Half of the solar energy reaching the Earth is in the infrared, most in the near infrared region. A quantum dot solar cell makes infrared energy as accessible as any other. Moreover, CQD offer easy synthesis and preparation.
Advantages of Nano Technology
If you gone through the above, you already have an idea of the advantage, but just for summarising, the advantages are as follows:-
- Nano tech. aim at alternative cheaper ways of developing solar panels in the hope of commercialising it to the masses.
- Using nano tech. makes manufacturing easier. Manufacturing highly efficient Si Solar panels are both difficult and cost extensive.
- Using Titanium Dye method help achieve high efficiencies at relatively low cost and effort.
- Nano tech. gives flexibility and strength to solar panels. Using of graphene based solar panel allows it to be used in making windows and transparent stuffs making extensive use possible.
- It provides alternative for replacing of bulk materials such as silicon, copper indium gallium selenide (CIGS) or cadmium telluride (CdTe).
- Quantum dots are viable for multi-junction solar cells, where a variety of materials are used to improve efficiency by harvesting multiple portions of the solar spectrum.
- And many more........
0 Comments