Improved performance of TiO2 nanoarray/BiOI heterojunction all-solid-state solar cells by incorporating BiFeO3 perovskite interlayer

The photovoltaic conversion of heterojunction solar cells relies on the interface properties between n-type and p-type semiconductors. N-type TiO2-nanoarray (NA), ferroelectric BiFeO3 interlayer, and p-type BiOI were used to fabricate a ternary bulk heterojunction using a solution-based method in this study. Solid-state solar cells of FTO/TiO2-NA/BiFeO3/BiOI/spiro-OMeTAD/Ag are constructed for the first time, and their photo-electric conversion performance is studied. The addition of a BiFeO3 interlayer at the interface between TiO2-NA and BiOI increased the solar cell open-circuit voltage (Voc) from 0.18 to 0.47 V and the short-circuit current (Jsc) from 0.29 to 0.54 μA/cm2, resulting in a nearly 5-fold increase in power conversion efficiency. The Kelvin Probe force microscope analysis confirmed that the polarization electric-field (Eself) generated by the BiFeO3 interlayer is directed toward BiOI, thereby increasing the surface potential and decreasing electron and hole back flows between TiO2 and BiOI. This additional electric field caused greater charge concentrations and a greater Voc. Furthermore, the Eself directed toward the BiOI increased the built-in electric field (Ebi) in the space charge area from TiO2 to BiOI, allowing for greater separation of photogenerated electrons and holes and thus raising the Jsc. The findings of this study suggested that manipulating internal electric fields via polarization could be an effective method for enhancing the performance of solar cells based on BiOI.