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 metal 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 across the UV-to-visible light, with responsivity tunable by the Ti3CNTx-toGO ratio. The optimized heterostructure achieves high photoresponsivity values of 0.16 mA W- 1 (cathodic) and 0.45 mA W- 1 (anodic), corresponding to 360-fold and 4-fold enhancements compared to pristine GO and Ti3CNTx, respectively. We untangle the strong PEPS effect, showing that Ti3CNTx facilitates efficient chargecarrier transfer and interfacial charge separation at the metal/semiconductor interfaces. These intriguing results highlight the potential of MXenes as building blocks for the design of highly sensitive optoelectronic devices that leverage the PEPS effect.