VATIS UPDATE Article

Solar cells made with films mimicking the structure of the mineral perovskite are the focus of worldwide research. But only now have researchers at Case Western Reserve University (CWRU), the United States, directly shown the films bear a key property allowing them to efficiently convert sunlight into electricity. Identifying that attribute could lead to more efficient solar panels. Electrons generated when light strikes the film are unrestricted by grain boundaries – the edges of crystalline subunits within the film – and travel long distances without deteriorating.

That means electric charge carriers that become trapped and decay in other materials are instead available to be drawn off as current. The scientists directly measured the distance traveled – called diffusion length – for the first time by using the technique called “spatially scanned photocurrent imaging microscopy.” Diffusion length within a well-oriented perovskite film measured up to 20 micrometers. “The findings indicate that solar cells could be made thicker without harming their efficiency,” said Xuan Gao, at CWRU.

In this research, Gao’s lab performed spatially scanned photocurrent image measurements on films made in the lab of CWRU professor Clemens Burda. Perovskite minerals found in nature are oxides of certain metals, but Burda’s lab made organo-metallic films with the same crystalline structure using methyl ammonium lead tri-iodide (CH3NH3PBI3), a three-dimensional lead halide surrounded by small organic methyl ammonium molecules that hold the lattice structure together.