Carbon Nano-Onions as a Functional Dopant to Modify Hole Transporting Layers for Improving Stability and Performance of Planar Perovskite Solar Cells

[Display omitted] •Novel CNOs and ox-CNOs are firstly used to modified PEDOT:PSS as HTLs.•Conductivity, work function, surface tension of HTLs are well improved.•Acidity and hydrophily of PEDOT:PSS are suppressed by ox-CNOs.•PSC based on modified PEDOT:PSS show enhanced PCE from 11.07% to 15.26%.•PSC based on modified PEDOT:PSS exhibit dramatic improvement of stability. Poly (3,4-ethylenedioxythiophene) polystyrene sulphonate (PEDOT:PSS) is the most widely used hole transporting layer (HTL) in planar perovskite solar cells, which shows excellent optical, electrical properties and good compatibility with low temperature, solution and flexible processing. Nevertheless, the acidic and hygroscopic property of PEDOT:PSS restricts its film conductivity and leads to the degradation of device stability. Herein, for the first time, we introduce the unprecedentedly zero-dimensional dopant of carbon nano-onions (CNOs) and the functionalized oxidized carbon nano-onions (ox-CNOs) to modify the PEDOT:PSS HTL. Besides the merits of high conductivity and suitable energy level, the CNOs and ox-CNOs modified PEDOT:PSS HTLs could provide a superior perovskite crystalline film with large-scale grains and orderly grain boundaries exhibiting a high surface tension with the hydrophobic property, resulting in a significant enhancement of PCE from 11.07% to 15.26%. Moreover, by suppressing the corrosion effect of PEDOT:PSS on ITO electrode, a dramatic improvement in the device stability has also been obtained.