Although the overall efficiency of this cell is still low compared to other types - about nine percent of the energy of sunlight is converted to electricity - the rate of improvement of the technology is one of the most rapid seen for a solar technology. The development is described in a paper, published in the journal Nature Materials, by MIT professors Moungi Bawendi and Vladimir Bulović and graduate students Chia-Hao Chuang and Patrick Brown.

The new process is an extension of work by Bawendi, the Lester Wolfe Professor of Chemistry, to produce quantum dots with precisely controllable characteristics - and as uniform thin coatings that can be applied to other materials. These minuscule particles are very effective at turning light into electricity, and vice versa. Since the first progress toward the use of quantum dots to make solar cells, Bawendi said: “The community, in the last few years, has started to understand better how these cells operate, and what the limitations are.”

The new work represents a leap in overcoming those limitations, increasing the current flow in the cells and thus boosting their overall efficiency in converting sunlight into electricity.

Many approaches to creating low-cost, large-area flexible and lightweight solar cells suffer from serious limitations - such as short operating lifetimes when exposed to air, or the need for high temperatures and vacuum chambers during production. By contrast, the new process does not require an inert atmosphere or high temperatures to grow the active device layers, and the resulting cells show no degradation after more than five months of storage in air.

Bulović, the Fariborz Maseeh Professor of Emerging Technology and associate dean for innovation in MIT’s School of Engineering, explained that thin coatings of quantum dots “allow them to do what they do as individuals - to absorb light very well - but also work as a group, to transport charges.” This allows the charges to be collected