Dye-sensitized solar cells with carbon nanotube transparent electrodes offer significant cost savings

A typical dye-sensitized solar cell comprises a porous layer of TiO2 nanoparticles immersed in an organic dye. The dye absorbs the sunlight and converts the energy into electricity, which flows into the TiO2 nanoparticles. The sun-facing side of the solar cell is usually covered with a transparent electrode that carries the charge carriers away from the TiO2 and out of the solar cell. “Unfortunately, ITO electrodes are brittle and crack easily,” says Huang. “They are also expensive and could incur up to 60% of the total cost of the dye-sensitized solar cell.”

Huang and his team therefore replaced the ITO electrode with a thin film of carbon nanotubes. Carbon nanotubes conduct electricity and are almost transparent, flexible and strong, which make them the ideal material for transparent electrodes. The only drawback is that photo-generated charge carriers in the nanotube may recombine with ions in the dye, which reduces the power conversion efficiency of the solar cell.

To overcome this problem, Huang and his team placed a TiO2 thin film in between the carbon nanotube thin film and the porous layer. They found that the performance of dye-sensitized solar cells with TiO2 thin film was significantly better than those without. However, they also found that the solar conversion efficiency of their new dye-sensitized solar cells was only 1.8%, which is lower than that of conventional solar cells using ITO electrodes. This is due to the higher electrical resistances and reduced optical transparency of the carbon nanotube films, which limits the amount of sunlight entering the cell.

“We are now studying different ways to enhance the conductivity and transparency of the films,” says Huang. “Furthermore, we are planning to replace the bottom platinum electrode with carbon nanotube thin film to reduce the cost of dye-sensitized solar cells further.”

If successful, the results could have a great impact on the cost and stability of dye-sensitized solar cells.

More information: Research article in Applied Physics Letters.

Provided by Agency for Science, Technology and Research (A*STAR)

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iPhone Daylight Savings Time Bug Strikes Again

The Day Light Savings (DST) started in the US few hours back when the clocks moved forward from 1:59 am to 3:00 am.

However, some iPhone users are reporting all sorts of problems with the DST changes. 

TUAW reports:

Several readers report that rather than jumping forward an hour last night as expected, their iPhone clocks actually shifted in the wrong direction -- back an hour -- because the automatic time zone adjustment went wonky. A reader in Nashville has a phone that thinks he's in Mountain Time; a reader in Florida's phone is convinced it should be on Chicago time. Our colleague Mel Martin lives in Arizona, which mostly does not observe DST at all; nevertheless, his phone (which had automatic time zone settings & location settings on) incorrectly jumped forward one hour.

This meant that the iPhone alarms went off at the wrong time for some of the users. This is not the first time that iPhone has been hit by the time bug, iPhone alarms had stopped working when we entered the new year and a DST bug had also affected iPhone users in 2010 and 2011.

In most cases, restarting the iPhone or enabling/disabling "Set Automatic" (timezone) settings (Settings->General->Data & Time) resolves the issue. It is also possible that some of these users are on an older version of iOS, which doesn't include a fix for the DST issue. So if you depend on your iPhone alarm clock then please be aware of the issue and possible workarounds to fix it.

Were you affected by the issue or your iPhone clock moved forward by an hour just fine? Let us know in the comments.

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