Enable strong electrical coupling between the InZnP@PbS collodial quantum dots in films via the two-step ligand exchange method

Colloidal quantum dots (CQDs) are promising materials for building next-generation solution-processed, high-performance, and low-cost optoelectronic devices. The photoelectric properties of the resulting films are not only determined by the intrinsic characteristics of the CQDs but are also significantly affected by the electrical coupling between them. However, enhancing the electrical coupling in CQD-based films is still a big challenge. In this work, a two-step ligand exchange strategy has been conducted to solve the above issue, where the InZnP@PbS CQDs have been used as the case. First, the Meerwein salt (Et3OBF4) solution in N, N-dimethylformamide (DMF) has been employed to peel off the native ligands that are strongly capped on the surface of oil-soluble CQDs, resulting in a neat surface. Second, iodide ions are linked to the neat surface of the CQDs to narrow the distance between them and passivate their defects, establishing strong electrical coupling. Transient surface photovoltage (TSPV) and photo-conductance tests confirm that the resulting InZnP@PbS–I CQDs films possess good photoelectric properties and stability. In the fabricated solid-state solar cells, 3.1 % of the photoelectric conversion efficiency (PCE) has been achieved under 1 sun. The current results are outstanding for III-V group CQD-based all solid-state solar cells.