Sunlight-driven　valorization　of　CO2　into　fuels　is　a　promising　solution　to　renewable　energy　storage,　but　the　design　of　an　integrated　and　efficient　solar-to-chemical　conversion　system　remains　challenging.　Herein,　an　all-solardriven　artificial　photosynthetic　system　(APS)　by　tailoring　photovoltaic-photoelectrochemical　cell　which　can　efficiently　produce　formic　acid　fuel　from　CO2　and　H2O　with　bias-free　illumination　is　demonstrated.　Guided　by　density　functional　theory　(DFT)　calculations,　a　BiOI-Bi　(BOI-Bi)　cathode　catalyst　is　synthesized,　which　is　highly　selective　for　CO2　to　HCOOH　conversion,　and　coupled　with　a　single　crystalline　argon-treated　TiO2　(TiO2-Ar)　photoanode,　whose　valence　band　edge　is　beneficial　for　the　oxidation　of　H2O　to　O2.　The　APS　exhibits　high　product　selectivity,　robust　activity　and　good　durability.　A　solar-to-HCOOH　selectivity　of　96.5%　is　obtained　with　a　HCOOH　yield　of　108.2　mmol　g-　1　h-　1　under　bias-free　illumination　of　AM1.5G.　The　device　can　operate　stably　for　at　least　12　h.　In　particular,　an　apparent　photon　quantum　efficiency　of　7.5%　and　a　solar-to-chemical　conversion　efficiency　(iSCC)　of　8.3%　are　recorded,　rivaling　all　the　incumbent　precious-metal-free　all-solar-driven　components　for　CO2-to-HCOOH　conversion.　This　study　highlights　the　potential　of　BOI-Bi　for　CO2　to　HCOOH　conversion　with　high　selectivity　and　its　integration　into　APS　system　to　realize　carbon-negative　solar-to-chemical　conversion　with　industrial　relevance.