Dramatic switchable polarities in conduction type and self-driven photocurrent of BiI₃ via pressure engineering

The intentional manipulation of carrier characteristics serves as a fundamental principle underlying various energy-related and optoelectronic semiconductor technologies. However, achieving switchable and reversible control of the polarity within a single material to design optimized devices remains a significant challenge. Herein, we successfully achieved dramatic reversible p-n switching during the semiconductor‒semiconductor phase transition in BiI₃ via pressure, accompanied by a substantial improvement in their photoelectric properties. Carrier polarity flipping was monitored by measuring the photocurrent dominated by the photothermoelectric (PTE) effect in a zero-bias two-terminal device. Accompanying the p-n transition, a switch between positive and negative photocurrents was observed in BiI₃, providing a feasible method to determine the conduction type of materials via photoelectric measurements. Furthermore, the combined effects of the photoconductivity and PTE mechanism improved the photoresponse and extended the detection bandwidth to encompass the optical communication waveband (1650 nm) under an external bias. The remarkable photoelectric properties were attributed to the enhanced energy band dispersion and increased charge density of BiI₃ under pressure. These findings highlight the effective and flexible modulation of carrier properties through pressure engineering and provide a foundation for designing and implementing multifunctional logic circuits and optoelectronic devices.