Improved passivation of PbS quantum dots for solar cells using triethylamine hydroiodide

Surface passivation of colloidal quantum dot (CQD) is one of the most crucial factors used to determine the power conversion efficiency (PCE) of CQD based solar cell (CQDSC) devices. In this work, we developed novel alkylammonium iodide based ligands, which can achieve more effective passivation of iodide for PbS based CQD than the conventionally used tetra-n-butylammonium iodide (TBAI). Sufficient ion dissociation property and higher acidity of triethylamine hydroiodide (tri-EAHI) led to the enhanced oleate ligand removal and iodide passivation compared to TBAI. Owing to the improved iodide passivation by tri-EAHI, the sub-bandgap trap density was successfully reduced, which offered lower doping density and higher electron mobility than TBAI. As a result, the depletion region in CQD active layers was widened, while the charge recombination in CQDSC was significantly reduced. The CQDSCs with the tri-EAHI achieved significantly higher PCE (9.84%) than that obtained using conventional TBAI (9.20%).