Graphite epoxy (GE) paste was prepared by thoroughly mixing Araldite Standard 2-part epoxy and graphite powder (4:3 weight ratio) . The GE paste was subsequently doctor-bladed onto the Ag contact of the OPV, forming a conductive, waterproof and adhesive layer that is directly interfaced with the IO-TiO2 electrode. A copper wire was then attached onto the electrode, followed by encapsulation of the entire device with Araldite 5-Minute Rapid 2-part epoxy to protect moisturesensitive components. The whole device was left to dry overnight under ambient conditions. Tandem devices were constructed in a similar manner, further wiring the organic photocathodes to BiVO4 photoanodes (defined active area of ~0.5 × 0.5 cm 2 , matching that of OPV) spin-coated with a TiCoOx water oxidation catalyst .