Photovoltaic Diode Effect Induced by Positive Bias Poling of Organic Layer-Mediated Interface in Perovskite Heterostructure α-HC(NH₂)₂PbI₃/TiO₂

It is shown that in the formamidinium (FA) lead iodide/titania heterostructure α-HC(NH₂)₂PbI₃/TiO₂ the organic layer-mediated interface, i.e., FAI/TiO₂, can induce photovoltaic diode effect via positive bias poling. The band gap of the heterostructure is reduced to zero upon the positive poling due to combined effects of ion diffusion, rotation of organic moieties, and ferroelectric redistribution. The perovskite part in the organic layer-mediated interface FAI/TiO₂ gives rise to a strong polarization of 18.69 μC cm⁻², compared to that (0.89 μC cm⁻²) in the inorganic layer-mediated interface PbI₂/TiO₂. The strong polarization of the organic layer-mediated interface is closely related to the diode effect associated with the reordering of the ferroelectric polarization and charge distribution, as a consequence of the mobility and rotation of organic moieties in FAI/TiO₂ upon the positive bias poling. The latter effect also provides an explanation on why the FAPbI₃-based devices can largely reduce the scanning hysteresis in the J–V curves (Yang et al., Science 2015, 348, 1234) and why the organic layer-mediated halide perovskite heterostructure is one of the most promising candidates for the fabrication of highly efficient solar cells or optoelectronic devices.