Multijunction solar cells like its other cousins (of solar cells) despite being little old, is a very promising technology.As the name suggest these cells literally have multiple junction (Figure 3 on left) on solar cells interconnected to each other. The top most cell is usually of higher bang gap (band gap represents the minimum energy that is required to excite an electron up to a state in the conduction band where it can participate in conduction)and the subsequent junctions are of lower band gap. With such arrangement, the top most junction would absorb some light (with high energy) and pass therest (via the tunnel junction) to the lower junctions. The subsequent junctions would do the same until light reaches the end of the cell. The light absorption spectrum of this solar cell is evident from (right hand side) figure 3 where close to half of the incident light (grey light which represents standard spectrum of AM 1.5) is absorbed by the cell. The current reported efficiency of this technology is around 40.7% (1 sun concentration) and 44.7% (at 100 suns concentration) but from a very small solar cell as evident from figure 4. It would however be interesting to see how soon we can commercialize such high efficient technology.

Figure 3: A representation of 3 layered Multijunction solar cell (left) and its absorption spectra (right) (Source:N.V.Yastrebova (2007), High-efficiency multi-junction solar cells: current status and future potential) Solar energy

Solar Power

Figure 4: Actual fabricated size of multijunction solar cell (Source: Fraunhofer)

We at Waaree Energies keep at both market and research trends. The time is not far when we would start using high efficient solar cells at commercially accepted rates. Additionally, we also expect a lot of variations and deviations in both cell architecture and materials which would enhance the efficiency and the power output of solar modules.

Let us all pledge to make solar energy the primary source of energy in the near future.

RAHE ROSHAN HAMARA NATION