An electron's lifetime can be determined by analyzing the green illuminating spot on perovskite crystals, shown as perpendicular ridges. Image: Rensselaer Polytechnic Institute.A promising semiconductor material could be improved if flaws previously thought irrelevant to its performance are reduced, according to a paper in Nature Communications. A group of researchers at Rensselaer Polytechnic Institute and other universities has shown that a specific defect impacts the ability of halide perovskite to hold energy derived from light in the form of excited electrons.
"Defects could be good or bad in semiconductors," said Jian Shi, associate professor of materials science engineering at Rensselaer Polytechnic Institute. "For some reason, people did not pay attention to dislocations in halide perovskite, but we have shown that this defect is a problem in halide perovskite."
Research on halide perovskite has rapidly improved the efficiency of this semiconductor in solar cells: from a 3% conversion of light to electrical energy to 25% –equivalent to state-of-the-art silicon solar cells – over the course of a decade. Researchers wrestled with silicon for decades to reach that level of efficiency.
Halide perovskite also has promising carrier dynamics, which are roughly defined as the length of time that light energy absorbed by the material is retained in the form of an excited electron. To make a good prospect for solar energy conversion, electrons in the material must retain their energy long enough to be harvested by an electrode attached to the material, thus completing the conversion of light to electrical energy.
As a further bonus, halide perovskite had long been considered ‘defect tolerant’, meaning flaws like missing atoms, shoddy bonds across grains of the crystal, and a mismatch known as crystallographic dislocation were not believed to have much impact on its efficiency. More recent research has questioned that assumption, however, and found that some defects do affect aspects of the crystal's performance.
Shi's team tested whether the defect of crystallographic dislocation impacts carrier dynamics in halide perovskite by growing the crystal on two different substrates. One substrate had a strong interaction with the halide perovskite as it was being deposited, producing a higher density of dislocations. The other had a weaker interaction and produced a lower density of dislocations.
The researchers found that dislocations can negatively impact the carrier dynamics of halide perovskite. Reducing dislocation densities by more than one order of magnitude increased electron lifetime by four times.
"A conclusion is that halide perovskite has a similar dislocation effect as conventional semiconductors," Shi said. "We need to be careful of dislocations in halide perovskite, which is a factor people have been ignoring as they work on this material."
This story is adapted from material from Rensselaer Polytechnic Institute, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.