Published on January 13th, 2015 | by James Ayre7
New Perovskite Blend Delivers What Researchers Say Is Highest-Efficiency Perovskite Solar Cell To Date
January 13th, 2015 by James Ayre
A new perovskite blend that addresses many of the most prominent previous issues with the technology has been developed by researchers in South Korea — reportedly resulting in what is, according to said researchers, the highest-efficiency perovskite cell to date.
To be specific, the issues in question that are addressed by the new blend are: for one, the “underlying instability” seen via the solar cells’ variability depending on the way that it’s measure; and, for two, the extension of the light-harvesting-wavelength-range of the solar cells.
By addressing these issues with perovskite solar cell technology — through the blending of the commonly used material methylammounium lead bromide, with a related (but relatively unused) compound by the name of formamidinium lead iodide — the researchers from the Korea Research Institute of Chemical Technology in Daejeon have reportedly succeeded in creating a perovskite solar cell with a conversion efficiency representing the top of the field.
Here are the technical specifics, via IEEE Spectrum:
Like methylammonium, formamidinium is a small, positively charged molecule made of carbon, hydrogen, and nitrogen. But formamidinium lead iodide absorbs light further into the near infra-red than its partner, potentially boosting the cell’s efficiency. Previous tests with the material had, however, shown that it was fairly unstable.
After testing several compositions, the researchers settled on an 85:15 mixture of the formamidinium and methylammonium perovskites. The resulting cell was much more stable and produced an average efficiency of 18.4%, they report this week in Nature. Seok says that this blend was also responsible for the record-breaking 20.1%-efficiency cell confirmed late last year by the US National Renewable Energy Laboratory in Golden, Colorado—the gold-standard in photovoltaic efficiency certification.
“In terms of absolute efficiency, this is probably the highest reported yet,” states Henry Snaith, a perovskite researcher based out of the University of Oxford.
The main takeaway probably, though, is that these new solar cells aren’t subject to the same variability/instability that has affected most other perovskite cells. As alluded to previously, perovskite solar cells are, for some reason or other, subject to variability with regard to voltage and efficiency — the conversion curves vary depending on “whether the voltage is increasing or decreasing, an anomaly known as hysteresis that may have led to overestimates of perovskite performance in the past.”
The implication of this is that the fundamental structure of the perovskite changes to a degree as the current moves through it. The new cells from South Korea, of course, are no longer affected to a notable degree in this way — thereby implying that they will possess a longer working life.