Tailoring of the PbS/metal interface in colloidal quantum dot solar cells for improvements of performance and air stability

Despite the outstanding advantages of a simple structure and cost-effectiveness of solution-based fabrication, Schottky junction quantum dot solar cells (QDSCs) often demonstrate low open-circuit voltage and power conversion efficiency (PCE) due to insufficient band bending at the QD/metal Schottky junction. Generally, this undesirable result stems from the presence of many defects at the QD/metal interface and the consequent Fermi-level pinning effect. Here, we show how the simple oxidation of PbS QDs at the PbS/metal interface can greatly improve the open-circuit voltage, fill factor, and PCE of Schottky junction QDSCs. On the basis of systematic analysis results using current–voltage characterization, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and light-soaking tests, we reveal that this enhancement originates from reduced interface states at the PbS/metal Schottky junction. Moreover, a significant enhancement of stability of the device is confirmed by the maintenance of >55% of its initial PCE even after 500 hours exposure in air without additional passivation.