Highly stable Al-doped ZnO by ligand-free synthesis as general thickness-insensitive interlayers for organic solar cells

Highly conductive and dispersible Al-doped ZnO (AZO) nanoparticles (NPs) have been successfully prepared by ligand-free colloidal synthesis at low temperature and stabilization by surfactant-aid including ethanolamine (EA), ethylenediamine (EDA), diethylenetriamine (DETA) and triethylenetetramine (TETA). Due to the strong intermolecular hydrogen-bonding interactions between AZO NPs and the amino groups from surfactants, the inevitable aggregation was suppressed and the surface defect sites were passivated obviously. The existence of electron transfer from the nitrogen of the amino groups to the zinc of AZO, led to a dramatic increase in electrical conductivity. A homogeneous current intensity value up to similar to 2200 pA for AZO tread by DETA was characterized by conductive atomic force microscopy (C-AFM), which was more superior than that of the reported sol-gel synthesized AZO with the assistance of EA surfactant (refer to 170.7 pA). Furthermore, non-fullerenes solar cells based on PBDB-T:ITIC with AZO-DETA (80 nm) yielded a best device efficiency of 10.7% and kept up prominent PCE exceeding 10% even with more thicker interlayer (95 nm).