Organic solar cells made from "small molecule" materials could soon become a viable competitor against polymer-based devices as a result of rapid efficiency gains coupled with innate cost and fabrication advantages.

While polymer-based cells currently dominate the field of organic solar power, scientists have recently made striking advances in the technology for small-molecule cells which could put their efficiency rates on par.

Researchers from the University of California at Santa Barbara, led by Alan J. Heeger, have found they can lift the efficiency of certain types of small-molecule organic solar cells from 6.02 per cent to 8.94 per cent – a whopping gain of almost 50 per cent – simply by adjusting the active layer’s thickness.

Heeger’s team achieved this adjustment via the insertion of a zinc oxide optical spacer between the active layer and the electrode, which puts the active layer in a more advantageous position within the cell’s optical electric field and raises its optical absorption by enabling it to reap more light.

According to Heeger’s team, the optical spacer increases light absorption in three ways: it raises charge collection efficiency, acts as a blocking layer for holes, and reduces the rate of recombination.

The advance puts small-molecule organic solar cells well within sight of the efficiency rates of polymer organic cells, which are at present just short of 10 per cent.

While small-molecule organic solar cells possess a number of advantages compared to polymer organic cells, their long-standing efficiency lags have thus far hampered the spread of their usage.

Their advantages include comparatively simple fabrication processes, better reproducibility, particles of roughly commensurate size permitting monodispersity, and high charge carrier mobility.

If small-molecule solar cells can achieve efficiency rates on par with their polymer rivals, they are likely to rise to a position of greater prominence as a result of this range of advantages.

Heeger’s team was able to increase efficiency by almost half with only a few modest changes, demonstrating that the devices still harbor tremendous potential for improvement.