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Friday, 19 August 2011

A one-pot synthesis provides a simpler and faster route to highly efficient solar cells

Aug 18, 2011

Preventing the recombination of free charges produced when light strikes a solar cell is one of the main goal of engineers attempting to extract the maximum energy conversion efficiency from their devices. One way to achieve this is by building into the cell a ‘heterojunction’ between positive (p) and negative (n) type semiconductors, which allows the light-induced positive and negative charge to escape the cell by moving in opposite directions at the heterojunction interface. Mingyong Han at the A*STAR Institute of Materials Research and Engineering and co-workers1 have now discovered a way to produce high-quality nanoscale heterojunctions, setting the stage for cheaper and more efficient photovoltaic devices.

Nanoscale semiconductor crystals provide enhanced surface area for light absorption and are also cheaper to produce than conventional lithography-patterned cell structures. However, it has been extremely difficult to form high-quality heterojunctions between n- and p-type semiconductors in a way that achieves the intimate inter-crystal contact needed to enhance device performance.

Resolving this problem requires a technique that can bind the two semiconductors together chemically. Previous studies have produced binary nanocrystals with a spherical ‘core–shell’ structure. Unfortunately, heterojunction based on these nanocrystals have low energy conversion efficiency because light has difficulty reaching the inner core. Han and his co-workers overcame this problem by adopting a different route for synthesis.
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