Carbon Inside...

The structure of the carbon nanomaterials employed, where the diameter of the semiconducting SWCNTs is in the 0.8–1.2 nm range. (Courtesy: Nano Lett.)

A new solar cell made from carbon nanotubes (CNTs) that is twice as good at converting sunlight into power than the best previous such cells has been unveiled by a team of researchers in the US. The National Renewable Energy Laboratory (NREL) has already independently certified the performance of the device – a first for a CNT-based solar cell.

Thin-film photovoltaic materials are better than conventional solar-cell materials (such as silicon) because they are lighter, more flexible and cheaper to make. They work by absorbing photons from sunlight and converting these into electron–hole pairs (or excitons). To generate electric current, an electron and hole must be rapidly separated before the two particles have a chance to come back together and be reabsorbed into the material. In solar cells, the exciton must quickly travel to another layer in the device (where the charge separation will occur) for the best light-absorption efficiencies.

Single-walled carbon nanotubes (SWCNTs) are ideal as thin-film photovoltaics because they absorb light across a wide range of wavelengths from the visible to the near-infrared and possess charge carriers (electrons and holes) that move quickly. However, most thin-film cells containing SWCNTs have so far suffered from limited current and voltage, and therefore poor power-conversion efficiencies.

Physics World: Making better solar cells with polychiral carbon nanotubes