Bulk photovoltaic and photoconductivity effects in two-dimensional ferroelectric CuInP₂S₆ based heterojunctions

The construction of two-dimensional heterojunctions has significantly expanded the modulation degrees of freedom in two-dimensional materials, which has led to the emergence of numerous advanced microelectronics and optoelectronic devices. Extensive research has been conducted on the photovoltaic and photoconductivity effects to achieve higher photodetection performance in heterojunction-based devices. However, the bulk photovoltaic effect, which has excellent potential for applications in self-powered optoelectronics, microelectronics, and energy conversion devices, has not received enough attention. Herein, we construct a two-dimensional ferroelectric heterojunction using multi-layered CuInP₂S₆ (CIPS) and MoS₂ nanoflakes and investigate its photoconductivity effect for photodetection. Furthermore, we observe and analyze the bulk photovoltaic effect in the heterojunction. The photoelectric effect in the MoS₂ layer contributes to the photoconductivity effect of the heterojunction, while the room-temperature polar ordering in CIPS contributes to the bulk photovoltaic effect. The heterojunction exhibits high specific detectivity (D^*) of 1.89 × 10⁹ Jones, when the optical power intensity is 4.71 mW/cm². Moreover, the short-circuit photocurrent density is high, reaching about 1.23 mA/cm² when the optical power intensity is 0.35 W/cm². This work highlights the potential application of two-dimensional ferroelectric materials in multifunction devices with self-powered detection and energy conversion capabilities.