Solution prepared O-doped ZnS nanocrystals: Structure characterization, energy level engineering and interfacial application in polymer solar cells

Doping impure atoms into host semiconductor nanocrystals is used to tune the properties and functions of semiconductor nanocrystals (NCs). Here, we demonstrate a solution method for preparing O doped ZnS (ZnS(O)) colloidal NCs. The as-prepared NCs have been proved to be consistent with the crystal structure of ZnS and Zn 3d-O2p hydrization existed in the as-prepared NCs as certified by O k-edge X-ray absorption spectra (XAS). The average size was measured to be about 8.5 nm by Transmission Electron Microscope (TEM). The role of pyridines was to control the size and tune the surface property. By doping oxygen into ZnS lattice, the energy levels of as prepared NCs were moved down, giving a better band alignment for photovoltaic application. When it was applied to modify ZnO interlayer and form ZnO/ZnS(O) bilayer in the polymer solar cells (PSCs), the optimal power conversion efficiency (PCE) of the device based on ZnO/ZnS(O) reached 8.85% (8.59 +/- 0.49%), which increased by 10% compared to ZnO-only control device with the optimal PCE of 8.00% (7.46 +/- 0.54%). The novel approach has been proved to be facile and scalable, paving the way for synthetizing O doped semiconductor nanocrystal.