Organic photocathodes and tandem devices. Encapsulation was necessary to prevent degradation of the organic photovoltaic device in aqueous buffer solution. A conductive graphite epoxy (GE) paste was first prepared by thoroughly mixing Araldite Standard 2-part epoxy and graphite powder in a 4:3 mass ratio. The paste was then spread homogenously onto the Ag contact of the photovoltaic device. For CO2R photocathodes, CoMTPP@CNT sheets were carefully attached to the wet GE paste and left to dry for 24 h. The CoMTPP@CNT composites were prepared via previously reported procedures. Next, wiring of the device was performed and all exposed edges were sealed with Araldite 5-Minute Rapid 2-part epoxy. For HER photocathodes, a 5 nm thin Pt catalyst was deposited onto the GE layer by magnetron sputtering using a Quorum Technologies Q150T ES instrument (10 mA sputter current, 5 nm min -1 sputter rate). To build a tandem device, the corresponding organic photocathodes were wired to BiVO4 photoanodes spin-coated with a TiCoOx water oxidation catalyst, prepared according to previous reports. PV characterisation. Organic PVs were characterised using a Sun 2000 Solar Simulator (Abet Technologies). A certified silicon reference solar cell RS-OD4 was used to calibrate the light intensity to 1 sun (100 mW cm -2 ). Reverse and forward J-V sweeps were conducted using a Keithley 2635 source meter at a scan rate of 100 mV s -1 in 20 mV steps between -0.1 V and 1.1 V. Devices were measured without additional masking at room temperature and the active area of each device was measured manually.