Low-Temperature-Processed ZnO Electron Transport Layers for PbS Colloidal Quantum Dot-Based Solar Cells

As an important electron transport layer (ETL) oxide, ZnO has been explored in colloidal quantum dot solar cells (CQDSCs), showing excellent power conversion efficiency (PCE), which however is significantly undermined when being subject to a low-temperature synthesis. To this end, in terms of utilizing 2-aminoethanol as a stabilizing ligand, highly stable ZnO nanoparticles were synthesized through a low-temperature (∼120 °C) reflux method and further utilized for the fabrication of the PbS CQDSCs, which were synthesized by oleic acid and 1-octadecence-assisted PbO decomposition strategy. The champion device with a configuration of glass/ITO/ZnO/PbS-EMII/PbS-EDT/Au achieves a high fill factor (FF) of 74.8% and appreciable PCE of 10.96%, slightly higher than that of the reference device with a ZnO ETL fabricated at 200 °C. This could be related to the high recombination resistance (Rrec of ∼465.8 ohms under light conditions) for the ZnO ETL-based PbS CQDSCs. What is more, these CQDSC devices demonstrate outstanding storage stability in an ambient environment, i.e., over 99% retention in PCE after 150 day storage. As highly efficient and stable CQDSCs are achieved, this work suggests a low-temperature strategy for ETL exploration. Our results may help to pave a feasible way for the development of low-temperature flexible PbS CQD solar cells.