Separation mechanism of photogenerated charges for p-type α-Bi2O3 nanoparticles with surface states

α-Bi2O3 nanoparticles were prepared via a sol–gel method. A strong absorption from the onset at 450 nm is observed, and α-Bi2O3 also exhibits an obvious and broad photovoltaic response from 325 to 500 nm with two ranges. The electric-field induced surface photovoltage spectroscopy increases evidently under positive bias, but it increases initially under weak negative bias and reaches saturation with the bias intensity stronger than −2 V. For this peculiar phenomenon about p-type characteristic of α-Bi2O3, we explained emphatically the micro-process and physical mechanism of the separation of photogenerated charges in the sandwich structure. Based on the results and our analysis, we think that both the build-in electric field due to Schottky barrier and surface states mainly contribute to the photovoltaic response for nanomaterial of α-Bi2O3.