A nanocomposite film based on poly(3,4-ethylenedioxythiophene):poty(styrene sulfonate) (PEDOT:PSS) modified with dual additives of carbon black (CB) and dimethyl sulfoxide (DMSO) was developed as a hole transport layer (HTL) in inverted planar perovskite solar cells (PSCs) for the first time. Taking advantage of the cooperative effect of CB and DMSO, the co-modified film of CB-DMSO-PEDOT:PSS shows superior capabilities to collect and transport the charge induced by reduced sheet resistance and to assist the growth of perovskite light harvest layer with enlarged grains in micron scale on its surface when compared with the single-modified films of CB-PEDOT:PSS and DMSO-PEDOT:PSS as well as the pristine film of PEDOT:PSS, Meanwhile, the co-modified film still preserves high transparency in the visible range with a transmittance of 89.8% at 550 nm and do not alter the transparency of the pristine film greatly. As a result, the PSCs made on the co-modified film as a HTL possess higher short-circuit photocurrent density and open-circuit voltage than the devices based on the single-modified and pristine films, leading to a remarkable enhancement in the power conversion efficiency. (C) 2017 Elsevier Ltd. All rights reserved.