High-Performance Up-Conversion Photodetectors with Zero-Barrier Interconnection via Self-Assembled Surface Dipoles

The performance of lead sulfide (PbS) quantum-dot-based up-conversion photodetectors is greatly limited owing to a large potential barrier at the interconnection layer between the photodetecting (PD) unit and light-emitting (LED) unit. Thus, very high driving voltage is required, rendering high energy consumption and poor working stability. By introducing azetidinium iodide (AzI) at the PD/LED interface, zero-barrier interconnection was achieved for the PbS-based infrared up-conversion photodetectors. The turn-on voltage under infrared illumination was greatly reduced to 1.2 V and a high photon-to-photon conversion efficiency (η_pp) of ∼3% was obtained at 3 V, showing a 10-fold enhancement compared to those previously reported devices. The mechanism for the regulation of interface energy level alignments was related to the self-assembly of the AzI dipole molecules, resulting from the van der Waals force between the S atoms in the ligands of PbS and the protonated H atoms around N atoms in AzI.