The PEC performance of encapsulated organic photocathodes was evaluated on a Newport Oriel 67005 solar light simulator equipped with an AM 1.5G optical filter, calibrated to 1 sun (100 mW cm -2 ) using a certified Newport 843-R optical power meter. The two-compartment PEC H-cell used contained either a Selemion or Nafion ion exchange membrane. A three-electrode set-up was adopted and comprised of an OPV|IO-TiO2 photocathode, a Ag/AgCl reference electrode (BASi MW-2030, stored in saturated NaCl) and a Platinum mesh counter electrode. The corresponding volumes of H2ase (100 pmol) or FDH (100 pmol) and CA (100 pmol) were drop-cast onto the OPV|IO-TiO2 electrode and incubated for 2-3 minutes prior to immersion in the buffer solution (50 mM NaHCO3 + 50 mM KCl, pH 6.45). Protein film voltammetry (PFV) and CPE scans were recorded on an Ivium CompactStat potentiostat under continuous stirring at room temperature. The buffer solution was purged with CO2 containing 2% CH4 as an internal standard before each experiment, and the entire cell was kept gas tight by sealing the septa with Loctite superglue. PFV scans were recorded between -0.1 V vs. RHE and 1.1 V vs. RHE at a scan rate of 10 mV s -1 and CPE experiments were conducted at 0.6 V vs. RHE over 10 h under chopped illumination (cycles of 50 min light on, 10 min light off). Experimentally measured potentials against Ag/AgCl were converted to the RHE scale using the equation: E (V vs. RHE) = E (V vs. Ag/AgCl) + 0.059 × pH + 0.197 V (at 298 K). Bias-free PEC tandems were evaluated in a single compartment PEC cell using a two-electrode set-up under 1 sun irradiation (AM1.5G, 100 mW cm -2 ). The BiVO4 photoanode was positioned in front of the OPV|IO-TiO2 photocathode in a back-to-back configuration and the irradiation window was defined by black masking tape on the BiVO4 photoanode, preventing illumination of the OPV|IO-TiO2 photocathode by unfiltered light. All data reported are the average of triplicate samples, with error bars referring to the corresponding standard deviation at each data point. EQE measurements were conducted using a monochromator coupled to a 300 W Xe light source (LOT-Quantum Design MSH-300) and an Ivium CompactStat potentiostat. The light intensity at each wavelength was measured using a Thorlabs PM100D power meter connected to a Thorlabs S302C thermal power sensor. The wavelength (full-width at half-maximum of 15 nm) was increased in 25 nm steps from 300 nm to 800 nm every 30 s. EQE was calculated using the equation: EQE (%) = hcJ/(eλPλ) × 100%, where h is the Planck constant, c is the speed of light, J is the photocurrent density, e is the elementary charge, λ is the wavelength and Pλ is the wavelength-dependant light intensity flux.