All-solution-processed ITO-free polymer solar cells fabricated on copper sheets

► We demonstrate cost-effective and ITO-free polymer solar cells fabricated on the flexible copper (Cu) sheets. ► The Cu electrode was used as a bottom cathode in inverted PSCs, and highly conductive PEDOT:PSS was used as a transparent top anode. ► The work-functions of Cu electrodes were engineered with an interfacial dipole layer to enhance the device-performance. ► The fabricated PSCs exhibited a power conversion efficiency of as high as ∼2.5%.