In-Plane BulkPhotovoltaic Effect in a MoSe₂/NbOI₂ Heterojunctionfor Efficient Polarization-SensitiveSelf-Powered Photodetection

Two-dimensional ferroelectric materials can generate a bulk photovoltaic effect, making them highly promising for self-powered photodetectors. However, their practical application is limited by a weak photoresponse due to a weak transition strength and wide band gap. In this study, we construct a van der Waals heterojunction using NbOI₂, which has significant in-plane polarization, with a highly absorbing MoSe₂ layer. We observe ultrafast hole transfer from MoSe₂ to NbOI₂ within 0.4 ps and electron transfer in the opposite direction within 3.8 ps, facilitating efficient charge dissociation and extraction. Applying a direct current electric field poling modulates the ferroelectric domains in NbOI₂, enhancing the bulk photovoltaic effect. This results in one of the highest responsivities for self-powered photodetectors (101.3 mA/W) at 0 V bias alongside excellent polarization sensitivity (∼7.58). This work advances the understanding of self-powering mechanisms via the bulk photovoltaic effect and proposes new strategies for future self-powered devices.