Balancing monomer and ionic ligand supply for scalable direct synthesis of short-wavelength infrared PbS quantum dot inks

PbS QDs, prized for their pronounced quantum confinement effect, can tune their bandgap across the near- to short-wave infrared (800–2500 nm) via size control, showing great potential in low-cost solar cells and infrared imaging. However, traditional synthesis using high-temperature organic-phase injection requires complex ligand exchange to remove long-chain insulating ligands. This process is time-consuming, costly, and prone to introducing surface defects that limit device performance. Recently, researchers have explored direct synthesis of inorganic ion-coordinated QD inks in polar solvents, but weak electrostatic repulsion often causes QD aggregation, making size control and scalable synthesis challenging.

A team led by Wanli Ma from Soochow University in China has developed a "low-temperature nucleation and high-temperature growth" strategy. This method suppresses precursor dissociation at low temperatures to reduce nucleation sites and then uses heating to promote monomer release and balance ligand supply. It effectively solves the problems of QD aggregation and size non-uniformity.

The results speak volumes: a single batch yields over 10 grams of QD solids—a 7-fold increase in production yield (14.2 g/L) compared to previous methods—while slashing costs to $5.7 per gram, down from $40.7/g for conventional approaches.

To validate their QDs’ optoelectronic prowess, the team fabricated solar cells using the inks, achieving a power conversion efficiency (PCE) of nearly 9%. “This efficiency is remarkable for SWIR-specific QDs, which are tailored for tandem solar cells as back-cell components,” noted Prof. Ma, a senior author of the study. “The real triumph lies in maintaining performance while scaling production—a hurdle that has stalled many promising nanomaterials.”

"The next step is to explore more efficient synthesis methods and improve the stability and performance of PbS QD materials," said Prof. Liu, a senior author of the study. "Our ultimate goal is to see these materials widely applied in practical optoelectronic devices, driving the development of next-generation solar cells and infrared imaging technologies."

This groundbreaking research not only advances the synthesis of PbS QD inks but also demonstrates their potential in optoelectronic applications. By addressing key challenges in size control and cost-efficiency, the study opens new avenues for the development of high-performance QD-based devices.

The full paper, “Balancing Monomer and Ionic Ligand Supply for Scalable Direct Synthesis of Short-Wavelength Infrared PbS Quantum Dot Inks,” is available in Nano Research, DOI: 10.26599/NR.2025.94907504.

About the Authors

Wanli Ma is currently a professor in the Institute of Functional Nano & Soft Materials (FUNSOM) at Soochow University. He received his PhD degree in 2006 from the University of California at Santa Barbara under the supervision of Prof. Alan J. Heeger. Before he joined Soochow University in 2010, he worked as a postdoctoral scholar in Prof. Paul Alivisatos’ group at Lawrence Berkeley national laboratory. His publications have been cited over 27000 times. His current research interest focuses on developing solution processed solar cells, including quantum dots, organic materials and perovskite.

Homepage: https://www.x-mol.com/groups/ma_wanli

About Nano Research

Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.