Dual-Polarity, Highly Responsive Broadband Photoelectrochemical Photodetectors Enabled by Ti3CNTx MXene/GO Heterostructure

Dual polarity photodetection devices are an important building block for multifunctional devices. In particular, photoelectrochemical photodetectors (PEC PDs) show great promise due to their ability to control photocurrent polarity by varying the incident light wavelength and the choice of electrolyte. However, achieving broadband dual-polarity PEC PDs that deliver high responsivity and bias switchable operation remains a significant challenge. 2D transition carbides, nitrides, and carbonitrides (MXenes) are emerging materials that combine high electrical conductivity, excellent electrochemical properties, and ease of solution processing, making them suitable for constructing multifunctional PEC PDs. Herein, we report the broadband dual-polarity photoelectrochemical photocurrent switching (PEPS) in Ti3CNTx MXene/GO operating under a small external bias. We employ a solid-solution Ti3CNTx MXene, which exhibits featureless optical absorption and high electrical conductivity, and hybridize it with semiconducting GO, which possesses abundant surface states and a tunable bandgap, to construct PEC PDs that exhibit the PEPS effect. Notably, Ti3CNTx/GO heterostructures show excellent bidirectional photoresponse under UV-to-visible light, with the direction of the and responsivity tuned by the Ti3CNTx-to-GO ratio. The optimized heterostructure achieves high photoresponsivity values of 0.16 mA/W (cathodic) and 0.45 mA/W (anodic), corresponding to 360-fold and 4-fold enhancements compared to pristine GO and Ti3CNTx, respectively. We untangle that the strong PEPS effect is observed due to the role of Ti3CNTₓ facilitating efficient charge carrier transfer and interfacial charge separation at the metal/semiconductor interfaces. These intriguing results highlight the potential of MXenes as building blocks for designing highly sensitive optoelectronic devices with the PEPS effect.