The Messy Path To Cleaner Energy

An artist's impression of a perovskite solar cell at the atomic level. Ella Maru Studio

Messy people of the world, rejoice. For too long we have suffered the sneers of those willing and able to keep things tidy, but now we learn messiness could save the world. Messy perovskite solar cells are not only cheaper to manufacture than their tidy counterparts, but capture more sunlight, opening the path to displacing fossil fuels from electricity production.

Today most solar panels are made using silicon. Dramatic falls in their prices have made solar power competitive across much of the world. However, silicon has some fundamental costs that are hard to avoid, raising serious questions about how much more savings can be squeezed out.

To make solar so cheap coal stands no chance, we probably need an alternative, and perovskite crystals are by far the most promising option, possibly after a transition period of silicon-perovskite hybrids

One reason silicon remains expensive is cell efficiency falls if they are not manufactured under exacting conditions, keeping the cell structure tidy. Researchers assumed the same applied when making experimental perovskite cells although they often lacked the equipment to make trial cells with the desired precision.

Cambridge University PhD student Sascha Feldmann decided to compare the efficiency of well-made cells with those thrown together higgledy-piggledy. He expected more ordering would make them better, but wanted to know how much.

Instead, Feldmann found rougher perovskites collect more solar energy than neat ones. Similarly, perovskite light-emitting diodes need less electricity to make the same glow. Less ordered compositions trap more charge carriers.

"It is actually because of this crude processing and subsequent de-mixing of the chemical components that you create these valleys and mountains in energy that charges can funnel down and concentrate in," Feldmann said in a statement. "This makes them easier to extract for your solar cell, and it's more efficient to produce light from these hotspots in an LED."

With the first mass production lines for perovskite cells currently under construction, Feldmann added that the discovery could save a lot of money. Instead of going to great lengths to maximize homogeneity, “We can show them that actually a simple inkjet printing process could do a better job," he said.

The discovery has been published in Nature Photonics, but Feldmann’s co-authors say the work is not finished. They anticipate there is an ideal amount of order in the chaos, and if they can find this, they could optimize cell efficiency.

The largest obstacle to perovskite sweeping the world remains its instability when exposed to even small amounts of water. Some test cells are showing more resilience, and if this can be locked in, the energy revolution may come sooner than you think. But it won't be neat.

 

A schematic of the surface of a perovskite cell, with h+ charge carrier holes and free electrons. Ellie Hall (Cambridge University).
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