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.
First, the researchers used a blend of surfactants under hot thermal conditions to produce copper(I) sulfide (CuxS), a well-known p-type semiconductor, in distinctively shaped hexagonal disks roughly 40 nanometers wide and 15 nanometers thick. The well-defined facets of these novel materials enabled the researchers to nucleate the crystallization of n-type cadmium sulfide (CdS) onto the outer edges of the crystals.
Next, through a process known as cation exchange, the researchers persuaded the n-type crystals to grow inward, effectively chemically converting a portion of the CuxS disks into CdS. “This method results in nano-heterostructures with the same morphology as the original material,” says Han. By carefully optimizing the reaction conditions, the researchers transformed the hexagonal nanodisk into a perfectly symmetric, side-by-side heterojunction. Zinc metals were also incorporated into the interface to further tweak its electrical performance.
Han notes that the CuxS–CdS heterostructure is promising for solar cell technology because of its dually accessible surface and an energy band alignment that drives strong charge separation. The team also expects to synthesize a wide range of new semiconductor pairs with this one-pot technique, taking advantage of the system’s extraordinary crystallization properties.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering
Regulacio, M. D. et al. One-pot synthesis of Cu1.94S–CdS and Cu1.94S–ZnxCd1–xS nanodisc heterostructures. Journal of the American Chemical Society 133, 2052–2055 (2011).
Argon is not the 'dope' for metallic hydrogen
24.03.2017 | Carnegie Institution for Science
Researchers make flexible glass for tiny medical devices
24.03.2017 | Brigham Young University
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy