Wavelength‐ and Humidity‐Controlled Reversible Photoconductivity Switching in a Novel Hybrid Polyoxoniobate

ABSTRACT Reversing the sign of photoconductivity in a single material has long been a formidable challenge, yet achieving this goal could open the door to a new generation of adaptive optoelectronics. Here, we report the first case of an inorganic‐organic hybrid polyoxometalate (POM), [Ni(BTP)] 4 [Nb 10 O 26 ]·35H 2 O ( 1 , BTP = Bis‐tris propane), capable of fully reversible switching between positive photoconductivity (PPC) and negative photoconductivity (NPC). This switching is dually controlled by excitation wavelength and relative humidity. Short‐wavelength excitation and low humidity give conventional PPC, whereas long‐wavelength excitation and high humidity induce NPC. This anomalous polarity inversion stems from the competition between two coexisting mechanisms: one is the photoelectric effect, which generates charge carriers within the POM; the other is the light‐induced water desorption process, which suppresses the electron donation from adsorbed H 2 O molecules, thereby reducing the carrier density. Resonant microcantilever measurements directly confirm the light‐induced water desorption process, and systematic wavelength/humidity‐dependent photoconductivity mapping reveals a well‐defined phase boundary that governs reversible PPC–NPC interconversion. This work represents a rare polarity‐switchable photoconductive material, expanding POM applications in optoelectronics.