Over 100-nm-Thick MoOx Films with Superior Hole Collection and Transport Properties for Organic Solar Cells

Herein, a novel and effective method to prepare n-doped MoOx films with highly improved conductivity is reported. The MoOx films are readily prepared by spin-coating an aqueous solution containing ammonium molybdate tetrahydrate and vitamin C (VC). As confirmed by UV-vis absorption, X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy measurements, Mo(VI) is partially reduced to Mo(V) by VC, resulting in the n-doping of MoOx. The conductivity of the n-doped MoOx (H:V-Mo) film can be enhanced by four orders of magnitude compared to pristine MoOx (H-Mo), that is, from 1.2 x 10(-7) to 1.1 x 10(-3) S m(-1). The device using a 10 nm H:V-Mo anode interlayer (AIL) exhibits comparable photovoltaic performance to a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-modified device. More importantly, the hole transport and collection properties of the H:V-Mo AILs show outstanding tolerance to thickness variation, that is, with increasing thickness of the H:V-Mo AIL from 10 to 150 nm, the V-oc and fill factor values of the devices remain unchanged. The device based on the blade-coated H:V-Mo AIL also has a high power conversion efficiency of 10.6%. To the best of the authors' knowledge, this work demonstrates the first example to prepare metal oxide AILs with outstanding tolerance to thickness, which is promising for the future large-area manufacturing.