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

We report on cost-effective and ITO-free polymer solar cells (PSCs) fabricated on the copper (Cu) sheets consisting mainly of a Cu electrode and a polyimide substrate. The Cu electrode was used as a bottom cathode in inverted PSCs, and each layer above the Cu sheet was all-solution-processed. The work-functions of Cu electrodes were engineered with an interfacial dipole layer to enhance the device-performance. Highly conductive poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (hcPEDOT:PSS) was used as a transparent top anode, and a photoactive layer was based on poly(3- hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The fabricated PSCs exhibited a power conversion efficiency (PCE) of ∼2.5%, demonstrating PSCs fabricated on Cu sheets have the great potential for cost-effective power generators. This study could be an important approach to the development of all-solution-processed and roll-to-roll PSCs using low-cost Cu electrodes as a cathode.