It sounds like a joke, but caffeine makes perovskite solar cells perform better. Mass production is a fair way off but it's quite possible a shot of coffee could be the missing ingredient required to make solar the dominant source of the world's electricity.
University of California, Los Angeles PhD students Rui Wang and Jingjing Xue are working on improving the performance of perovskite solar cells and found the answer to two of the major problems they are seeking to overcome may lie at the bottom of a coffee pot.
It started as a joke. "One day, as we were discussing perovskite solar cells, our colleague Rui Wang said, 'If we need coffee to boost our energy then what about perovskites? Would they need coffee to perform better?'" Xue recalled.
Mad as the idea may seem, the team tried replacing the dimethyl sulfoxide they had been using to stabilize cells with caffeine. They found lead ions grabbed the caffeine as tightly as any student on a desperate all-nighter the day before an assignment deadline. Crystals formed more slowly, producing better final structures.
Caffeinated cells produced turned 20 percent of the light falling on them into electricity, while the decaf equivalents managed just 17 percent. Even with the molecular jolt, Wang and Xue admit in their paper published in Joule that their work is not setting efficiency records, but the figures are impressive for such an early stage of development. More importantly, the cells with caffeine were much more stable at extended temperatures of 85ºC (185ºF), addressing perovskite cells' biggest problem; the way their performance can quickly decay when exposed to heat or moisture.
Silicon dominates the solar market. Despite the enormous decreases in cost, and continuing progress in the efficiency, of silicon cells, they are thought to have performance ceilings and price floors, both of which we may be approaching. A variety of alternative cell types with greater potential exist, but so far their drawbacks have restricted these to niche applications.
Perovskite is the great hope. Although it still doesn't match silicon in several important respects, it has managed in a few years to replicate achievements that took other cell types decades. If current progress can be maintained, perovskite cells could soon produce electricity at prices no fossil fuel will ever match.
Perovskite crystals are made using inexpensive manufacturing techniques from the widely available elements calcium, oxygen, and titanium. When small amounts of certain metals are added, they become solar cells, with properties that vary depending on the elements used to dope them. Sports may consider a caffeine an illegitimate performance enhancer, but in the race to find the combination of additives that will harvest the most sunlight, manufacturers will have no such qualms.