Thin Films Power Electronics Mixed In Fabrics

Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) reported significant advances in the thermoelectric performance of organic semiconductors based on carbon nanotube thin films that could be integrated into fabrics to convert waste heat into electricity or serve as a small power source.

The research demonstrates significant potential for semiconducting single-walled carbon nanotubes (SWCNTs) as the primary material for efficient thermoelectric generators, rather than being used as a component in a “compositethermoelectric material containing, for example, carbon nanotubes and a polymer. The discovery is outlined in the new Energy & Environmental Science paper, Large n- and p-type thermoelectric power factors from doped semiconducting single-walled carbon nanotube thin films.

There are some inherent advantages to doing things this way,” said Jeffrey Blackburn, a senior scientist in NREL’s Chemical and Materials Science and Technology center and co-lead author of the paper with Andrew Ferguson. These advantages include the promise of solution-processed semiconductors that are lightweight and flexible and inexpensive to manufacture. Other NREL authors are Bradley MacLeod, Rachelle Ihly, Zbyslaw Owczarczyk, and Katherine Hurst. The NREL authors also teamed with collaborators from the University of Denver and partners at International Thermodyne, Inc., based in Charlotte, N.C.

Ferguson, also a senior scientist in the Chemical and Materials Science and Technology center, said the introduction of SWCNT into fabrics could serve an important function for “wearable” personal electronics. By capturing body heat and converting it into electricity, the semiconductor could power portable electronics or sensors embedded in clothing.


New Efficiency Record with Dual-Junction Solar Cell

Scientists at the Energy Department’s National Renewable Energy Laboratory (NREL) and at the Swiss Center for Electronics and Microtechnology (CSEM) have jointly set a new world record for converting non-concentrated (1-sun) sunlight into electricity using a dual-junction III-V/Si solar cellThe newly certified record conversion efficiency of 29.8 percent was set using a top cell made of gallium indium phosphide developed by NREL, and a bottom cell made of crystalline silicon developed by CSEM using silicon heterojunction technology. The two cells were made separately and then stacked by NREL.

dual junctio solar cell

It’s a record within this mechanically stacked category,” said David Young, a senior researcher at NREL. “The performance of the dual-junction device exceeded the theoretical limit of 29.4 percent for crystalline silicon solar cells.”

Young is co-author of a paper, “Realization of GaInP/Si dual-junction solar cells with 29.8 percent one-sun efficiency,” which details the steps taken to break the previous record. His co-authors from NREL are Stephanie Essig, Myles Steiner, John Geisz, Scott Ward, Tom Moriarty, Vincenzo LaSalvia, and Pauls Stradins. The paper has been submitted for publication in the IEEE Journal of Photovoltaics.

Essig attracted interest from CSEM when she presented a paper, “Progress Towards a 30 percent Efficient GaInP/Si Tandem Solar Cell,” to the 5th International Conference on Silicon Photovoltaics, in Germany in March. “We believe that the silicon heterojunction technology is today the most efficient silicon technology for application in tandem solar cells” said Christophe Ballif, head of PV activities at CSEM.

CSEM partnered with the NREL scientists with the objective to demonstrate that 30 percent efficient tandem cells can be realized using silicon heterojunction bottom cells, thanks to the combination with high performance top cells such as those developed by NREL,” said Matthieu Despeisse, the manager of crystalline silicon activities at CSEM.

The record was published in “Solar cell efficiency tables.”


Perovskite Could Convert Two-Third of Solar Energy To Electricity

Scientists at the Energy Department’s National Renewable Energy Laboratory (NREL) have demonstrated a way to significantly increase the efficiency of perovskite solar cells by reducing the amount of energy lost to heat.

peroskite solar cell

Present-day photovoltaic cells can only effectively utilize about a third of the available energy, with another third lost to heat and the rest lost to other processes instead of being converted to electricity. The NREL research determined that charge carriers created by absorbing sunlight by the perovskite cells encounter a bottleneck where phonons (heat carrying particles) that are emitted while the charge carriers cool cannot decay quickly enough. Instead, the phonons re-heat the charge carriers, thereby drastically slowing the cooling process and allowing the carriers to retain much more of their initial energy for much longer periods of time. This potentially allows this extra energy to be tapped off in a hot-carrier solar cell.

The theoretical limit of how much solar energy perovskite cells can convert to electricity if the hot-carriers are utilized could climb from about 33% to 66%. Additional research is needed, including tests on perovskites made from other materials.

Ye Yang is lead author of the paper. NREL colleagues David Ostrowski, Ryan France, Kai Zhu, Jao van de Lagemaat, Joey Luther and Matthew Beard also contributed to the research. A paper on the discovery, “Observation of a hot-phonon bottleneck in lead-iodide perovskites,” was published online this week in the journal Nature Photonics. The research also will appear in the January print edition of the journal.