Highly Stabilized Quantum Dot Ink for Efficient Infrared Light Absorbing Solar Cells

Liquid-state ligand exchange provides an efficient approach to passivate a quantum dot (QD) surface with small binding species and achieve a QD ink toward scalable QD solar cell (QDSC) production. Herein, experimental studies and theoretical simulations are combined to establish the physical principles of QD surface properties induced charge carrier recombination and collection in QDSCs. Ammonium iodide (AI) is used to thoroughly replace the native oleic acid ligand on the PbS QD surface forming a concentrated QD ink, which has high stability of more than 30 d. The ink can be directly applied for the preparation of a thick QD solid film using a single deposition step method and the QD solid film shows better characteristics compared with that of the film prepared with the traditional PbX₂ (X = I or Br) post-treated QD ink. Infrared light-absorbing QDSC devices are fabricated using the PbS-AI QD ink and the devices give a higher photovoltaic performance compared with the devices fabricated with the traditional PbS-PbX₂ QD ink. The improved photovoltaic performance in PbS-AI-based QDSC is attributed to diminished charge carrier recombination induced by the sub-bandgap traps in QDs. A theoretical simulation is carried out to atomically link the relationship of QDSC device function with the QD surface properties.