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Stanford post-doctoral scholar Tomas Leijtens and Professor Mike McGehee examine perovskite tandem solar cells Image credit LA Cicero

Researchers from Stanford University, California (US), and the University of Oxford (UK) have created new forms of perovskite using tin and other inexpensive, abundant materials. Their resulting robust, all-perovskite tandem solar cell converts sunlight into electricity with an efficiency of 20.3%, thus, has shown it can rival and even outperform conventional devices made of silicon. 

"We have developed a new perovskite semiconductor that does a great job harvesting infrared photons," confirms Tomas Leijtens, co-lead author of the Science Journal paper "Perovskite-perovskite tandem photovoltaics with optimized bandgaps" and postdoctoral scholar in materials science and engineering at Stanford. "When used together with another perovskite semiconductor that specializes in harvesting visible photons, we are able to convert solar energy into electricity with 20% efficiency. We think we are going to be able to increase the efficiency to 30%, which could revolutionize the solar industry."

Perovskite solar cells have been demonstrated to be efficient and have the potential to be processed at low costs. Multijunction solar cells can reach the highest theoretical performances but have traditionally been made of costly III-V semiconductors. "Making a multijunction solar cell from two perovskite semiconductors opens a new path towards a PV technology with the highest performance but at the low costs associated with perovskite semiconductors and thin-film manufacturing," Leijtens says. 

Potentially game-changing innovation

"This is the first technology that has the potential to significantly outperform crystalline silicon PV without a large price tag," the researcher notes. "In fact, the manufacturing and installation costs should be much lower." He backs up his projection with the argument that since the costs associated with installing photovoltaics are typically dominated by the installation, improving solar energy conversion efficiency is one of the key drivers for overall cost reduction. 

The Stanford-Oxford study, thus, could significantly catalyze the advancement of solar energy. "Our study identifies a solar cell architecture that has the potential to reach the highest possible solar energy conversion efficiency," Leijtens says. "This is enabled by the new semiconductors we have developed as well as the way in which we have designed the solar cell and stacked the different layers together to form one effective device."

Cross-section of a new tandem solar cell designed by Stanford and Oxford scientists. The brown upper layer of perovskite captures low-energy lightwaves, and the red perovskite layer captures high-energy waves. (Image credit: Scanning electron microscopy

Path to market, promises

Using this technology, Leijtens and his team aim to approach the 30% solar energy conversion efficiency benchmark in the next three to five years. "We are an academic research group, so we are more focused on improving the performance and durability of these solar cells, rather than the path to market," he points out. "However, we envision that the unique ability of this technology to make PV modules that are high performance, lightweight, flexible and cheap to manufacture should make it extremely promising for numerous applications and markets."

Major obstacles overcome

Talking about the challenges with this particular research project, the expert elaborates that prior to this work, multijunction perovskite solar cells did not exist or perform well for two reasons: Neither an appropriate semiconductor to harvest the infrared part of the solar spectrum nor an efficient multijunction solar cell design and architecture existed. "These were the challenges we had to solve," Leijtens says. The material they have developed for harvesting the infrared part of the solar spectrum contains tin, which was previously thought to be unstable in perovskite solar cells. Surprisingly, the team found that their devices containing tin could be made to be extremely stable. 

Extremely high-throughput manufacturing

Talking about the fabrication of this new type of all-perovskite tandem solar cell, Leijtens shares that they made thin films of the perovskite semiconductor by depositing a solution and letting the solvent evaporate away. "On a manufacturing level, this means that the layers can be printed on reel-to-reel printing presses with extremely high throughput," he says. 

Optimization: Harvesting even more IR photons and increasing stability

The materials scientist and his colleagues will continue to work on the solar cell design to improve its ability to harvest infrared photons. "Tweaking the composition of the perovskite semiconductors should yield improvements. We will also thoroughly study the stability of this solar cells design," Leijtens says. "In the next few years, we hope to obtain performances over 30% in stable multijunction perovskite solar cells," Leijtens once again pronounces, in conclusion.

Written by Sandra Henderson, Research Editor, Solar Novus Today

Labels: All-perovskite tandem solar cell,thin-film solar cells,perovskite solar cells,Stanford University,University of Oxford,perovskite semiconductor,Tomas Leijtens,multijunction solar cells

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