Light hits a solar cell, and inside, charges are born, hot and bothered. Like a person after a jog, they carry extra energy. To deliver current to an external circuit, they need to cool down and reach the edges of the crystal. If cooling drags on, part of the energy is wasted.

The scientists built three identical solar cells but with different perovskite "fillings": one based on methylammonium, one on a mix of methylammonium and formamidinium, and one on pure formamidinium. They illuminated the cells with short pulses and watched how quickly the charges rolled down from high energy steps to lower ones — where they can be harvested into a wire.

It turned out that the speed of this "rolling down" depends strongly on the composition. Charges cool fastest in formamidinium perovskite, slower in the mixed one, and quite leisurely in methylammonium. The difference is not by orders of magnitude, but it is noticeable and important for engineers.

So even a small substitution of one component in the perovskite crystal can change the entire energy pathway. It's like choosing the right lubricant for a mechanism: the parts are the same, but losses are smaller. Now solar cell developers have a tool to tailor perovskite composition for specific applications — for example, for windows that generate power or for lightweight rooftop panels.