A highly efficient fullerene-free polymer solar cell (PSC) based on PDCBT, a polythiophene derivative substituted with alkoxycarbonyl, achieves an impressive power conversion effi ciency of 10.16%, which is the best result in PSCs based on polythiophene derivatives to date. In comparison with a poly(3-hexylthiophene): ITIC-based device, the photovoltaic and morphological properties of the PDCBT: ITIC-based device are carefully investigated and interpreted.