The early onset potentials of OPV photocathodes in neutral buffers and complimentary light absorption enabled the assembly of unassisted artificial leaves with BiVO4 photoanodes for O2 evolution (see UV-vis spectra in Supplementary Figs. and). The nanostructured photoanodes were prepared by BiOI electrodeposition and annealing in the presence of a vanadium source, whereas a transparent and amorphous TiCoOx (TiCo) layer was employed as a water oxidation catalyst. CV scans of OPV|GE|Pt -BiVO4 tandem devices indicated a very early onset bias of -0.9 V for overall water splitting, and a photocurrent density of around 0.8 mA cm -2 at 0 V applied bias (Fig. ). This was consistent with CV scans of the individual photoelectrodes, which showed a good overlap at a photocurrent density of 0.9 mA cm -2 and an operating potential of 0.8 V vs. RHE (Supplementary Fig. ). The overall photocurrent was limited by the wide bandgap BiVO4 photoanode, as the OPV photocathode attained up to 2.5 mA cm -2 even under the light filtering effect of BiVO4. Tandem devices could produce 50.0±11.9 µmol cm -2 H2 (72.6±7.0% FY) and 20.3±8.0 µmol cm -2 O2 (57.9±9.4% FY) over 10 h CA under bias-free conditions, corresponding to solar-tofuel efficiencies of 0.63±0.15% (H2) and 0.51±0.19% (O2) (Fig. ; see unassisted PEC comparison in Supplementary Table ). The high photovoltages of both light absorbers allowed OPV|GE|CoMTPP@CNT -BiVO4 tandems to demonstrate unassisted syngas production from aqueous CO2. The tandems displayed an onset voltage of -0.4 V and a bias-free initial photocurrent density of 0.2 mA cm -2 (Fig. and Supplementary Fig. ). A CO:H2 selectivity of 0.93±0.31 was achieved after 10 h CPE under 0 V applied bias, with STF efficiencies of 0.086±0.009%(H2) and 0.087±0.030% (CO) respectively. A similar product rate and CO:H2 selectivity could be sustained for standalone artificial leaves, where both photoelectrodes were directly connected (Fig. ,e and Supplementary Table ). Accordingly, an OPV|GE|Pt -BiVO4 PEC tandem produced 118.4 µmol cm -2 H2 and 39.4 µmol cm -2 O2 during 24 h of irradiation, whereas 11.4 µmol cm -2 H2, 11.4 µmol cm -2 CO and 8.5 µmol cm -2 O2 were obtained with the OPV|GE|CoMTPP@CNT -BiVO4 device.