High-performance inverted planar perovskite solar cells based on efficient hole-transporting layers from well-crystalline NiO nanocrystals

NiO is an important hole-transporting material for preparing inverted planar perovskite solar cells (PSCs). Apart from some complicated preparation methodologies such as doping routes, pulsed laser deposition, atomic layer deposition and high temperature spray pyrolysis, the simpler solution-processed method can also achieve high-quality NiO hole-transporting layers for efficient inverted planar PSCs. One of the prerequisites for solution-processed high-quality NiO hole-transporting layers is pre-synthesized highly crystalline NiO nanocrystals (NCs). Here, we use the sophisticated solvothermal method to synthesize highly crystalline NiO NCs. The oleylamine ligands are used to well control the nucleation and growth of NiO NCs and achieve good colloidal stability in toluene, which make for high-quality NiO hole-transporting layers by solution process. The related measurements and analysises reveal that the as-prepared NiO hole-transporting layer shows faster hole extraction, more effectively suppressed recombination and fewer surface trap states than the typical poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) hole-transporting layer, finally contributing to superior photovoltaic performance of the corresponding device. This work highlights the feasibility of colloidal chemical synthetic route for pre-synthesizing highly crystalline and well dispersed semiconductor NCs suitable for preparing efficient PSCs by the simple solution-processed protocol.