The power conversion efficiencies (PCEs) of the state-of-the-art organic tandem solar cells are steadily improved in the range of 10–12%, which can be mainly attributed to the design and development of highly efficient absorbers with complementary absorption spectra. However, the impressive recorded efficiencies are only achieved for devices spin-coated in an inert atmosphere, which does not directly contribute to the commercialization of the organic photovoltaic technology. Herein, we perform a systematic study of PTB7-Th-based single-junction solar cells fabricated under various conditions. The relatively low photovoltaic performance and poor environmental stability of the air-processed devices are successfully improved by a post-treatment with alcohol-based solvents. The effect of solvent treatment is valid for both regular and inverted device architecture. Tandem devices fabricated by doctor-blading in air achieve a high PCE of 10.03% along with an unprecedentedly high FF of 76.6%.