Chemical Mixture Erases Crystal Defects to Boost Perovskite Solar Cell Power

Perovskite solar cells have spent more than a decade tantalizing the photovoltaics community with a seductive promise: a semiconductor that can be printed like ink, layered on top of conventional silicon, and tuned to harvest sunlight with remarkable efficiency. Yet for all their promise, these manufactured crystals have been held back by a stubborn, invisible enemy. Deep inside their crystalline lattices, atomic-scale defects form during fabrication, trapping and dissipating the very energy the material is supposed to deliver. Now a team led by researchers at Princeton Engineering, the University of California-San Diego and Sungkyunkwan University in Korea reports a surprisingly elegant fix, and the results, published in the journal Science, suggest that the perovskite revolution may have just moved considerably closer to reality.

The new technique hinges on a counterintuitive insight about how perovskites crystallize. By adding a mixture of zinc bromide and methyl ammonium chloride early in the fabrication process, the researchers discovered they could dramatically reduce the number of defects that form in the crystal structure as the material solidifies. The consequences of that seemingly small intervention are striking. In defect-free perovskites produced this way, electrons retain the excess energy they absorb from sunlight roughly ten times longer than in untreated material. According to Dane deQuilettes, assistant professor at Princeton and a senior author on the paper, the improvement could translate into a one percent gain in power generation even for the most cutting-edge perovskite solar cells already in existence — a meaningful margin in a field where incremental gains are fiercely contested.

To understand why those microseconds matter, it helps to grasp what actually happens inside a working solar cell. When sunlight strikes a semiconductor, photons transfer their energy to electrons, lifting them into an excited state. The whole point of a photovoltaic device is to harvest that excess energy as electricity before the electrons relax back down and release it as heat. Defects in the crystal lattice act like traps along this pathway, snaring excited electrons and squandering their energy before it can be collected. The longer electrons can hold onto their excess energy — a property measured in microseconds in these experiments — the more opportunities there are to extract useful power. In deQuilettes’ measurements, electrons in the treated perovskites retained their energy for up to 300 microseconds, roughly a hundred thousand times longer than in many other semiconductors.

The discovery itself was born of serendipity. A few years ago, Jason Yoo, a first author on the paper who was then a researcher at the Korea Research Institute of Chemical Technology, noticed that his samples were behaving in ways he could not explain. He reached out to deQuilettes, whose laboratory specializes in developing tools to probe how electrons behave and interact inside perovskites. “He told me the samples were behaving like nothing he had seen before,” deQuilettes recalled. “He asked if I could help study them.” What deQuilettes found when he examined the samples amazed him: the extraordinary carrier lifetimes that would eventually form the basis of the Science paper.

The chemistry behind the breakthrough is as subtle as it is effective. The key, deQuilettes explained, is that the two added chemicals — zinc bromide and methyl ammonium chloride — must have a lower melting point when combined than either does alone, much as adding salt to ice lowers its freezing point. Such mixtures are known as eutectics, and the paper’s title, “Volatile eutectics to tailor crystallization for perovskite optoelectronics,” reflects this principle. By introducing a volatile eutectic during the early stages of fabrication, the researchers changed the way the perovskite crystal grows, steering it toward a more ordered lattice with fewer of the atomic-scale imperfections that plague conventionally processed films. “We opened up this new class of chemical mixtures that improve the performance of perovskites,” deQuilettes said.

The broader context makes the advance especially significant. Most solar cells installed around the world today are made of silicon, a material prized for its durability but constrained by its physics and its energy-intensive manufacturing. Perovskites, by contrast, can be prepared from liquid precursors and printed in sheets, like ink on newsprint, potentially making them cheaper and more sustainable to produce at scale. Increasingly, the two technologies are being combined rather than competing: a thin coat of perovskite layered over a silicon solar cell forms a tandem device that generates about 40 percent more power than a cell made from either material alone. The catch has always been that the printing and layering process tends to introduce those damaging atomic-level defects, blunting the perovskite layer’s contribution. Fewer defects mean a more efficient perovskite layer, which in turn means more efficient tandem modules rolling off future production lines.

The timing could hardly be more pointed. Global electricity demand is climbing rapidly, driven in no small part by the explosive growth of artificial intelligence and the datacenter infrastructure that underpins it. “The whole solar industry has been asking, what are the next set of technologies that are going to contribute to energy production?” deQuilettes noted. A one percent improvement in power conversion may sound modest, but in the economics of utility-scale solar — where installations span thousands of acres and margins are measured in fractions of a cent per kilowatt-hour — even single-digit percentage gains compound into substantial additional generating capacity. And because the improvement is achieved through chemistry during fabrication rather than through expensive post-processing, it is the kind of change that manufacturers could in principle adopt without redesigning their entire production workflow.

Perhaps the most intriguing implications reach beyond photovoltaics altogether. Because electrons in the treated perovskite persist in their excited state for hundreds of microseconds — an eternity by semiconductor standards — the material opens possibilities that conventional semiconductors simply cannot offer. “Energy is living in the material for so long, it broadens what’s actually possible with a semiconductor,” deQuilettes said. Long carrier lifetimes are coveted not only in solar cells but in a range of optoelectronic applications, from light-emitting devices to photodetectors and potentially quantum technologies, where the ability of a material to hold onto excitation energy determines what device architectures are feasible. The researchers emphasize that the discovery has raised more questions than it has answered. “It’s been really eye-opening,” deQuilettes added, suggesting that the eutectic approach may be only the first entry in what could become a broad family of defect-mitigating chemical mixtures.

The study was a genuinely international effort. In addition to deQuilettes at Princeton and Yoo and Bong Joo Kang at the Korea Research Institute of Chemical Technology, the author list spans Connor J. Dolan, Zhewen J.D. Deng, Jack R. Palmer, Kelly X. Vences and David P. Fenning at the University of California-San Diego; Seongsik Nam, Jinho Lee, Kyu Min Kang, Daesoo Kim, Jang Hee Cho, Donghyuk Chung and Seong Sik Shin at Sungkyunkwan University in Korea; Rushik Desai and Arun Mannodi-Kanakkithodi at Purdue University; Niranjana Mohan Kumar, Mariana I. Bertoni and Arkita Chakrabarti at Arizona State University; Yanqi Luo, Barry Lai, Zhonghou Cai, Martin V. Holt and Tao Zhou at Argonne National Laboratory; Andrew M. Kiss at Brookhaven National Laboratory; and In Sun Cho at Ajou University and Dong Hyun Kim and Jun Hong Noh at Korea University. That breadth of expertise — spanning synthesis, ultrafast spectroscopy, synchrotron characterization and computational modeling — reflects the multidisciplinary challenge of understanding and controlling defects at the atomic scale.

For a field that has weathered its share of hype and hard lessons, the new result offers something refreshingly concrete: a reproducible chemical strategy, published in a peer-reviewed journal, that measurably extends carrier lifetimes by an order of magnitude and points toward real gains in device performance. Perovskites have always been crystals of extraordinary promise; the challenge has been coaxing that promise out of an imperfect lattice. With volatile eutectics now shown to tailor crystallization in a way that suppresses defects at their source, researchers have a new tool — and a new class of chemistry to explore — in the long effort to build better solar technology, one crystal at a time.

Subject of Research: Defect mitigation in perovskite solar cells using volatile eutectic chemical additives during fabrication

Article Title: Building better solar tech, a crystal at a time

Article References: Building better solar tech, a crystal at a time. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: perovskite, solar cells, crystal defects, eutectics, photovoltaics, tandem solar cells, semiconductors, carrier lifetime, zinc bromide, methyl ammonium chloride, Princeton University, Science journal