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  Date: 14/06/2015

Solar PV cell efficiency research focus on material and structure innovation

Due to the green energy priority all over the world and continued fall in the average selling price of solar PV cells , the global demand for solar PV is expected to reach 75 GW in 2019, which is 66% higher than in 2014, according to IHS. IHS has forecasted the average selling price of solar to decline by 27% between 2015 and 2019, reaching $0.45 per watt (W). All this positive market growth resulting in focused research in increasing the conversion efficiency of solar PV cells. Below are some of the latest activities in this area:

1. imec announced a new record efficiency for its large area n-type PERT (passivated emitter, rear totally diffused) crystalline silicon (Cz-Si) solar cell, now reaching 22.5 percent . IMEC says it is the highest efficiency achieved for a two-side-contacted solar cell processed on six inch commercially available n-type Cz-Si wafers without the use of passivated contacts. N-type silicon solar cells perform better than p-type solar cells in withstanding light-induced degradation and are more tolerant to common metal impurities.

imec is innovating on the material and architecture in improving n-PERT solar cell performance by using Ni/Cu/Ag front contacts, rear local contacts, a diffused front surface field (FSF) and a rear emitter. The cells achieved an independently confirmed open-circuit voltage (Voc) of 689mV, a short-circuit current (Jsc) of 40.3 mA/cm2, and 80.9 percent fill factor (FF), reports Imec.

Imec said it has also been exploring n-type PERT cells with a rear side p-type emitter using epitaxial growth or heterojunction processes to achieve even power conversion efficiency.

2. In another case of solar cell efficiency enhancement, researchers at the University of Aalto, Finland able to achieve efficiency by using black silicon solar cells. They could solve the issue of carrier recombination which is common in black silicon and achieve efficiency up to 22.1%. Researchers could check the recombination problem by applying an aluminium film to shield chemically as well as charge carriers. Using this method they could reduce the recombination of freed electrons to 4% compared to 50% earlier.

The Black silicon is nothing but fabricating nanoscale needles on top of silicon so that the light falling of the solar panel doesn't get reflected, that's why it derives the name black silicon. Black silicon also traps light coming from very low angles, a good efficiency can be achieved even though light is falling at low angle on the surface of silicon. The Black silicon doesn't require antireflection coating which saves the manufacturing cost. The researchers here have used P type silicon instead of N type silicon. There are chances of further increasing the efficiency if N type silicon is used.

3. While this is about the research on crystalline silicon solar PV cells, There is also news of record efficiencies achieved in thin-film solar cells too. A team of Japanese researchers could achieve efficiency of 13.6% at triple junction thin-film solar cell. This team have used a concept called light trapping to up the conversion efficiency. The advantage of thin-film solar cells over crystalline silicon are they are cheaper to make.

4. There is another interesting material called the Perovskite explored for solar photovoltaics. The solar PV cells made using Perovskites costs even less than silicon-based thin-film solar cell. To give you some achievement in this area: Imec has achieved 8% conversion efficiency by using Perovskite material in thin-film solar PV cells. Imec is working to further increase the conversion efficiency of silicon solar cells by creating a stack with a perovskite cell on top of a silicon solar cell. The perovskite cell will capture the light which is not absorbed by silicon, as such enabling conversion efficiencies of more than 30 percent, explain Imec in its release.
Author: Srinivasa Reddy N
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