A BiVO4 -PVK|GE|Pt PEC tandem could attain a reproducible onset voltage of -0.8 V and photocurrents of ~0.6 mA cm -2 at 0 V applied bias, displaying a minimal photocurrent decay and no visible photocathode degradation during a 10 h indoor stability test (Supplementary Figs. 8,11,12, Movie 1). The H2 FY amounted to 99.2% after 10 h, corresponding to a 0.69% solar-to-fuel conversion efficiency (STF). Accordingly, the evaporated perovskite device structure and hydrophobic graphite paste coating resulted in a threefold improvement in performance and stability over our previously reported 10 cm 2 perovskite-BiVO4 devices for overall water splitting, which could only sustain photocurrents of 0.2 mA cm -2 at 0 V applied bias, with an onset voltage of -0.5 V and complete photocurrent degradation within 3 h. 10 cm 2 BiVO4 -PVK|GE|Cu92In8 tandems were also benchmarked under 1 sun illumination for 36 h, comparable to daylight availability over a 3-day outdoor test (Fig. , Supplementary Figs. , Movie 1). CV scans of tandem devices displayed an onset voltage of -0.5 V, indicating that artificial leaves can operate in the absence of external bias (Supplementary Fig. ). Accordingly, a PEC tandem sustained a steady-state photocurrent density of around 0.1 mA cm -2 during long-term CPE at 0 V applied bias (Fig. , Supplementary Fig. ), representing a tenfold increase in stability over earlier, Field's metal encapsulated devices. The artificial leaf produced 88.5 µmol CO and 319.5 µmol H2 over 36 h (see amounts normalised per area in Fig. ), corresponding to faradaic yields of 17.7% (CO) and 59.3% (H2), with a CO:H2 ratio of 0.24:1. Accordingly, the 10 cm 2 device attained STF values of 0.098% (H2) and 0.032% (CO), which compare favourably to small-scale artificial leaves with active areas <1 cm 2 (Supplementary Table ). This performance was reproducible, with a second prototype yielding 79.6 µmol CO and 215.6 µmol H2 over 36 h, with FYs of 22.3% (CO) and 60.3% (H2), a CO:H2 ratio of 0.37:1, and STF values of 0.062% (H2) and 0.025% (CO) (Supplementary Fig. ).