Novel black bismuth oxide (Bi 2 O 3 ) with enhanced photocurrent generation, produced by high-pressure torsion straining

Bismuth oxide (Bi 2 O 3 ), a yellow semiconductor ceramic, is considered as an advanced photoactive energy material, but its activity still needs further improvement for practical applications. In this study, black Bi 2 O 3 with nanocrystalline structure and large fraction of oxygen vacancies is synthesized by mechanical straining via the high-pressure torsion (HPT) method. The black oxide exhibits enhanced light absorbance under both UV and visible lights. It shows a bipolar photocurrent behavior with up to six times higher photocurrent density compared with the unprocessed yellow Bi 2 O 3. This study shows the high potential of severely-strained black Bi 2 O 3 for photovoltaic, photoconductivity and photocatalytic applications.