Ma Wanli's team at Soochow University published a research paper titled "Overcoming efficiency and cost barriers for large-area quantum dot photovoltaics through stable ink engineering" in the journal Nature Energy. Shi Guozheng from Soochow University/The University of Electro-Communications, Japan, and Ding Xiaobo from Soochow University are the co-first authors of the paper, and Liu Zeke, Hiroshi Segawa from the University of Tokyo, Japan, Shen Qing, and Ma Wanli are the co-corresponding authors of the paper.

Key Highlights: This paper develops a strategy for manipulating the solution chemistry of lead sulfide (PbS) colloidal quantum dot inks prepared by a low-cost direct synthesis method. By creating an iodine-rich environment in a weakly coordinating solvent, the iodine lead salts are converted into functional anions, forming a robust surface shell that prevents quantum dot aggregation and epitaxial fusion, resulting in a stable ink. A certified efficiency of 13.40% was achieved in a 0.04 cm² cell, and the active area was expanded 300-fold to a 12.60 cm² module with a certified efficiency of 10%.

The modern information age relies on highly crystalline semiconductors produced through energy-intensive, top-down manufacturing processes, which are subject to high material costs. Colloidal quantum dots (CQDs), as an emerging material, offer the potential for bottom-up design through solution processing, preserving the semiconductor's crystalline properties and offering broad applications in mesoscale technologies. However, the current instability and high cost of CQD inks limit the scalable production of CQD electronic devices. The stability of CQD inks not only determines the feasibility of industrial large-scale production but also influences the nanomorphology and microstructural formation during CQD assembly. Therefore, developing stable, scalable, and cost-effective CQD inks is crucial for realizing efficient CQD electronic devices.
Based on this, a team led by Ma Wanli, Liu Zeke, Shen Qing, and Hiroshi Segawa from the Institute of Functional Nanomaterials and Soft Matter at Soochow University, Japan, and the University of Tokyo, Japan, developed a solution chemical engineering strategy for preparing lead sulfide (PbS) CQD inks using a low-cost, direct synthesis method. By creating an iodine-rich environment in a weakly coordinating solvent, iodoplumbide is converted into functional anions, which then coalesce into a robust surface shell. The fully charged electrostatic surface layer prevents CQD aggregation and epitaxial fusion, resulting in a stable ink. By eliminating fusion-induced interband states, compact CQD films with three-dimensional uniformity, flattened energy levels, and improved carrier transport are printed. A certified efficiency of 13.40% was achieved in a 0.04 cm² cell, and the active area was expanded 300-fold to a 12.60 cm² module with a certified efficiency of 10%.
This research systematically reveals the surface defects and energy loss mechanisms caused by anion deficiency in low-cost, directly synthesized quantum dot inks. Through the synergistic effect of a weakly coordinating solvent and an iodine-rich environment, lead iodide complexes are converted into functional anions, forming an anti-fusion surface shell that inhibits irreversible aggregation and lattice fusion of quantum dots. Based on this strategy, the printed quantum dot film exhibits three-dimensional uniformity, a flat band structure, and efficient carrier transport. Laboratory-scale cells achieved a certified efficiency of 13.40%, and for the first time, a 10% efficiency breakthrough was achieved in a module with an active area of 12.60 cm². This ink simplifies processing, reduces costs ($0.06/W), and is environmentally friendly, potentially promoting the industrialization of quantum dot electronic devices.