A bandgap‐tunable KNbO3 ferroelectric ceramic was prepared by introducing Bi/Co ion. The existence of mixed valence states of Co2+/Co3+ in the system induced the bandgap reduction and its tunable behavior. KNbO3–BiCoO3 solid solutions showed a typical orthogonal perovskite structure and maintained good ferroelectricity (Ps = 15.13 µC/cm2) and high‐field polarization ability. The devices based on the .98KNbO3–.02BiCoO3 sample exhibited an improved short‐circuit photocurrent density (Jsc) of 19.2 nA/cm2 under simulated solar radiation, and this was further enhanced to 79.8 nA/cm2 after a 60‐kV/cm polarizing. The structural analysis of the samples after polarization reveals the effect of ferroelectric polarization on photovoltaic performance. This work provides new insights into the effects of ferroelectric polarization on photovoltaic performance.