NEWS ANALYSIS
respectively). But III-V quantum dots promise to bring a better solar cell. Compared to the active layers used in conventional devices, these semiconductor crystals can be tuned to absorb light over a much wider range of wavelengths, boosting conversion efficiencies.
What’s more, by working with quantum dots rather than planar layers, researchers avoid the strains that build up at the interfaces between different materials, opening the door to the growth of novel material combinations that simply wouldn’t be possible in conventional devices.
With this in mind, Liu and colleagues intend to develop a “completely different” quantum dot solar cell system grown on silicon, both with and without a thin germanium buffer layer.
This bold move could swipe away the high GaAs substrate prices of current CPV cells and capitalise on cheap CMOS manufacturing costs. The end result
could be a very cheap, yet highly efficient solar cell with, as Liu says, at least a 30 percent conversion efficiency.
“IQE provides silicon wafers with the germanium buffer layer, and at the same time we are also working with Sharp to develop GaAs solar cells on germanium-on-silicon,” the researcher explains.
“But we are also working on the direct growth of III-V multi-junction solar cells on silicon with another industrial partner. If we can use the direct growth approach on silicon, this is better... We are academics, and we want to try any possibility.”
Right now, the team is looking at a range of materials systems based on III-V quantum dots that absorb near the peak of the spectrum, around 1eV.
As Liu explains: “We have previously worked with lasers and have now found that using the InAs/GaAs quantum dot system is not ideal for absorption in solar
cells, so we are looking at alternative systems with a different bandgap alignment and long carrier lifetime.”
The key contenders are metamorphic InAs/GaAsSb and InP/GaAsP quantum- dot systems, and the researchers will also explore such materials combinations in the context of an intermediate band structure solar cell.
Here an intermediate energy band is introduced into the energy gap of a single semiconductor junction. Such a structure promises conversion efficiencies up to 63percent, but only if the photo- generated carriers in the intermediate level can be channelled solely to the host material.
Clearly such a device will require much more work yet, but as Liu highlights: “EPSRC is taking a longer term view by funding research such as this.
Maybe industry is struggling, but for the academic, it’s definitely a good area to be working right now.“
Submit your Lab & Fab article
Research is the foundation for the growth of the Compound Semiconductor industry.
If you want to highlight the important breakthroughs that you make, submit your latest research stories to
SuWestwater@angelbc.co.uk
It is imperative that Compound Semiconductor remains a timely resource for this industry, so we
are only interested in highlighting very recent work reported in academic papers.
Therefore, please only consider writing a short piece highlighting your work if you have a
journal paper that has been accepted and about to appear in press, or a paper that has been published within the last month.
For further details of what we are looking for, see
www.compoundsemiconductor.net/csc/labfab-news.php June 2013
www.compoundsemiconductor.net 19
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191