Recent studies have highlighted the significant influence of external electric fields on the photovoltaic effects of ferroelectric materials. Here, the ferroelectric semiconductor (1−x)Bi_0.5Na_0.4K_0.1TiO₃–xSmCoO₃ (abbreviated as xSmCo, where x ranges from 0.00 to 0.1) was synthesized using the solid-state method, achieving a narrowed optical band gap of 2.20–3.09 eV. Under the combined action of electric and light fields, the short-circuit photocurrent density (J_sc) increases from 44 to 269 nA·cm⁻². When thermal fields are also applied, J_sc further rises to 924 nA·cm⁻². However, the application of additional mechanical or magnetic fields reduces J_sc to 165 and 92 nA·cm⁻², respectively. The mixed valence states of Co²⁺/Co³⁺ introduce a high density of oxygen vacancies, facilitating band gap narrowing. The substitution of Sm³⁺ ions at the A-site preserves the ferroelectric properties. In ferroelectric ceramics, the remnant polarization (P_r) establishes a strong internal electric field, which is crucial for photo-induced charge carrier dynamics. These findings demonstrate that external fields—light, electric, thermal, mechanical, and magnetic—affect spontaneous polarization strength, internal field stability, and charge carrier transitions within the electronic bands. This study provides new insights into the interplay of multiple field interactions and their effects on the photovoltaic properties (J_sc/V_oc) of ferroelectric oxide materials.