We demonstrated an organic-inorganic composite as hole transport layer consisting of water-free PEDOT:PSS and tungsten oxide (WO3) nanoparticles, which enhanced the power conversion efficiency of normal-structure perovskite solar cells (PSCs). The PSC employing the WO3/PEDOT:PSS film as a hole transport layer exhibited better device stability and improved power conversion efficiency (PCE) with approximately 20% performance enhancement. The highest PCE obtained from WO3/PEDOT:PSS device was 15.1%, owing to simultaneous increments on short circuit current, open circuit voltage and fill factor. WO3 nanoparticles can fill out the pinholes of porous PEDOT:PSS layer, demonstrating a void-free and homogenous HTL surface. WO3/PEDOT:PSS composite demonstrated much higher charge conductivity and hole mobility than pristine PEDOT:PSS layer. The interface of perovskite absorber and WO3/PEDOT:PSS HTL also contained less defect density. The superior performance of WO3/PEDOT:PSS composite was attributed to the reduced current leakage, enhanced hole extraction characteristics, and less trap-assisted interfacial recombination via current density - voltage, electron microscopy (SEM, AFM and c-AFM), electrochemical impedance spectroscopy (EIS) and space-charge limited current-voltage (SCLC) measurements and analysis. (C) 2019 Elsevier Ltd. All rights reserved.