A technique for producing high-performance inverted perovskite solar cells, called solution-process secondary growth (SSG), was shown to increase the voltage of inverted perovskite solar cells by as much as 1.21 V. Inverted planar perovskite solar cells can simplify device structure and reduce costs, compared with conventional solar cells. However, lower open-circuit voltages in perovskite cells can result in lower power-conversion efficiencies (PCEs) than in conventional cells. The SSG technique reduces nonradiative charge-carrier recombination — a process whereby energy and efficiency are lost in perovskite cells. SSG was used to produce a wider bandgap top layer and a more n-type perovskite film, mitigating nonradiative recombination and leading to an increase in open-circuit voltages of 100 mV. These performance improvements do not compromise the quality of the solar cell or the electrical current flowing through a device, researchers said. The team of researchers from Peking University and the universities of Surrey, Oxford, and Cambridge tested the technique on a device that recorded a PCE of 20.9 percent. According to the team, this is the highest certified PCE for inverted perovskite solar cells ever recorded. “Our new technique confirms that there is a lot of promise with perovskite solar cells, and we aim to explore this new and exciting area more in the future,” said researcher Wei Zhang from the University of Surrey. The research was published in Science (doi:10.1126/science.aap9282).