We report a method to prepare molybdenum oxide thin films using the stable cetrimonium bromide-modified MoO3 (CTAB-modified MoO3) precursor solution. The effect of thermal treatment on the optical, crystalline, morphologic properties and surface wettability is greatly obvious because of the pyrolytic decomposition of CTAB. The highly efficient and stable polymer solar cells (PSCs) have been also fabricated by adopting CTAB-modified MoO3 nanocomposite films as the novel and universal anode buffer layers (ABLs). The P3HT:ICBA based solar cells with CTAB-modified Mo03 at 200 degrees C heat treatment exhibit an best power conversion efficiency (PCE) of 5.80% with long-term stability, and the PTB7:PC71BM based solar cells with CTAB-modified MoO3 at 200 degrees C heat treatment show an best PCE of 8.34% with long-term stability, which are higher than that of the corresponding devices with PEDOT:PSS films. The improvement in device performance is mainly due to the agreeable electrical properties and enhanced charge extraction of the CTAB-modified MoO3 ABLs, and CTAB modification to the MoO3 surface can effectively passivate its surface traps, suppress the recombination loss of carriers. The surface of CTAB-modified MoO3 films is also more hydrophobic than that of the PEDOT:PSS. In a word, these indicate the CTAB-modified MoO3 films may be used as a novel and generally applicable hole transport layer for high-efficiency and ambient stable polymer solar cells.