Chili Pepper Compound Is Spicing Up Solar Cell Performance

These may look like any other semiconducter chip, but they are actually solar cells given extra kick with the molecule that makes chilli peppers taste hot. Jin Yang

We don't recommend licking solar cells, but soon you might get a familiar tingle if you do, as researchers improved solar cells efficiency and stability using capsaicin, the molecule that makes chili peppers spicy. Following the discovery of increased production from solar cells dosed with caffeine, researchers seem to be dropping in their favorite chemical pick-me-ups in their quest for clean energy.

Theoretically, perovskite solar cells can be a little more efficient and much, much cheaper than existing silicon versions. A successful transition from lab bench to rooftop would make daytime electricity unprecedentedly cheap, and the world will be on the path to a safer future. Despite extraordinarily rapid progress, however, challenges remain.

One of the biggest is known as nonradiative recombination, where defects in cell materials allow electrons and holes to combine, reducing current flow. Dr Qinye Bao of East China Normal University is one of many scientists around the world seeking to bring this under control. Bao reports in Joule capsaicin flipped the active layer 100 nanometers below the surface from p-type (having a surplus of holes for electrons) to n-type (having excess electrons).

Adding caffeine to give perovskites an efficiency boost was a joke someone decided to try, only to be surprised at its success. Bao's chili powder has a different tale. "Considering the electric, chemical, optical, and stable properties of capsaicin, we preliminarily found that it would be a promising candidate," he said in a statement

Consequently, the team was not surprised it worked. Nevertheless, they had to do a lot of experimentation to find the ideal recipe for spicy solar cells. Bao and co-authors report 0.1 percent capsaicin by weight added to a MAPbl3 perovskite precursor provide the benefits they have observed.

The maximum efficiency Bao was able to achieve with capsaicin added was 21.88 percent. This is well below the record for any type of perovskite cells, which are now in the mid-20s. However, it's the highest ever achieved for polycrystaline MAPbl3 cells, and close to the 21.93 percent record for the harder to make monocrystaline MAPbl3. This cell type is considered a strong candidate for commercialization, despite not being the current efficiency leader.

Meanwhile, cells that were identical other than the absence of capsaicin achieved only 19.1 percent. More importantly, the capsaicin-infused cells are more stable, maintaining good production levels for promising periods of time.

Besides increasing the density of surplus electrons in the cells' surface film, capsaicin reduces the number of defects.

However, much you may fancy your solar power red hot, Bao's cells as fuel, not food. MAPbI3 stands for methylammonium lead triiodide, so these cells are definitely poisonous. However, Bao and others are seeking to replace the lead, the quantities of which are already very small in perovskites with both metal and organic alternatives. If that can be done using molecules you can grow in your garden, all that better.

At the least, it has to be better than powering the world out of the main component of farts.

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