Titanium oxide (TiOX) is an effective electron transport layer in polymer solar cells (PSCs). Here, we report an efficient inverted polymer solar cell based on P3HT and fullerenes using a high density, single-step solution processed amorphous TiOX (alpha-TiOX) film as an electron transport layer. The alpha-TiOX film was prepared by spin coating tetrabutyl titanate (TBT) isopropanol solution onto ITO coated glass in a glovebox filled with N-2 and then annealing at different temperatures in air. The films with high light transmittance are very smooth. The PSCs with the alpha-TiOX electron transport layer showed enhanced photovoltaic performance in comparison with the device using PEDOT:PSS as the anode buffer layer. The optimized power conversion efficiency (PCE) of the PSCs based on P3HT/PC61BM and P3HT/PC71BM with the alpha-TiOX electron transport layer reached 4.25% and 4.65%, respectively, under AM1.5G illumination (100 mW cm(-2)). In addition, the PSCs with the alpha-TiOX electron transport layer exhibited good stability. The results indicate that facile preparation of alpha-TiOX films using cheap TBT is promising for high-efficiency PSCs and large-scale fabrication of flexible electronics.