(CH3NH3)3Bi2I9 perovskites have attracted enormous attention due to their lower toxic and more stable nature than CH3NH3PbI3 counterparts. However, higher bandgap and lower carrier mobility hinder the application of (CH3NH3)3Bi2I9 in optoelectronics. Hence, we employed carbon doping of Co3O4 hole extractors to reduce the bandgap of (CH3NH3)3Bi2I9, minimize non – radiative recombination rate and improve surface morphology of the (CH3NH3)3Bi2I9 particles. Consequently, photodetectors based on carbon-doped Co3O4 display reduced internal resistance, high photocurrent and low dark current values. The fabricated photodetectors display high responsivity (1.56 × 106 μA/W), high detectivity (5.74 × 1012 Jones), high sensitivity (8.23 × 103) and fast optical switching times (< 10 ms) values under device testing conditions of 2.0 V bias voltage, 10 mW/cm2 power intensity of solar illumination and ambient room conditions. The linearity and stability of the photodetectors over wide range of light intensities and 100 optical switching cycles were also demonstrated respectively.