Effects of trap density on separation efficiency of photogenerated carriers for Sb-SnO2/TiO2 heterojunction semiconductors

In this paper, heterojunction semiconductors of Sb-SnO2/TiO2 were prepared with varying molar ratios of Sb-SnO2 to TiO2. The separation efficiency of the photogenerated carriers was characterised by the surface photovoltage (SPV) technique, and the trap density was measured by an electrochemical method. The trap density was measured to be 7·48×1016, 6·01×1016, 5·43×1016, and 6·61×1016 cm−2 for TiO2 and Sb-SnO2/TiO2 films with molar ratios of 1, 2, and 3%, respectively. The SPV enhancement was estimated to be 1, 1·36, 7·64, and 6·36 for TiO2 and Sb-SnO2/TiO2 films with molar ratios of 1, 2, and 3%, respectively. The results indicate that SPV enhancement increases with decreasing trap density, which demonstrates that the trap density is an important factor affecting the separation efficiency of photogenerated carriers in heterojunction semiconductors.