Organic Ligand-Free ZnO Quantum Dots for Efficient and Stable Perovskite Solar Cells

Zinc oxide (ZnO) is a promising electron-transport layer (ETL) in thin-film photovoltaics. However, the poor chemical compatibility between commonly used sol-gel-derived ZnO nanostructures and organo-metal halide perovskites makes it highly challenging to obtain efficient and stable perovskite solar cells (PSCs). Here, a novel approach is reported for low-temperature processed pure ZnO ETLs for planar heterojunction PSCs based on ZnO quantum dots (QDs) stabilized by dimethyl sulfoxide (DMSO) as easily removable solvent molecules. With no need for the ETL doping or surface modification, the champion PSC comprising the mixed-cation and mixed-halide Cs-5(MA(0.17)FA(0.83))(95)Pb(I0.83Br0.17)(3) absorber layer reaches a maximum power conversion efficiency of 20.05%, which is significantly higher than that obtained for a reference device based on a standard sol-gel-derived ZnO nanostructured layer (17.78%). Thus, along with the observed better operational stability in ambient conditions and elevated temperature, the champion device achieves the state-of-the-art performance among reported non-passivated pure ZnO ETL-based PSCs. The improved photovoltaic performance is attributed to both a higher uniformity of the surface morphology and a lower defects density of films based on the organometallic-derived QDs that are likely to ensure the enhanced stability of the ZnO/perovskite interface.