Electrolyte-Induced Band Bending and Barrier Tuning to Enhance Photodetection in Inkjet-Printed Organic–Inorganic Heterojunctions

Hybrid organic–inorganic heterojunctions have attracted considerable interest in optoelectronic applications, as they combine the excellent electronic transport of inorganic semiconductors with the ease of processing and tunability of organic conductors. While the performance of such heterojunctions is strongly governed by their built-in electric field and interfacial band alignment, strategies for actively tuning these parameters in printed bulk heterojunctions have remained largely unexplored. In this regard, here we show an inkjet-printed bulk heterojunction diode with semiconducting amorphous indium gallium oxide (a-IGO) and conducting poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), whose interfacial barrier can be dynamically modulated by a solvent (dimethyl sulfoxide, DMSO) or a composite solid polymer electrolyte (CSPE). Systematic studies of pristine, DMSO-treated, and CSPE-treated devices reveal that DMSO enhances charge transport in PEDOT:PSS, while mobile ions of CSPE penetrate the polymer matrix and accumulate at the heterojunction interface. Capacitance–voltage measurements show that ionic screening increases the built-in potential from 0.36 to 0.70 eV by inducing additional band bending within a-IGO. Consequently, the off-current decreases by more than two orders of magnitude, accompanied by a substantial enhancement in rectification ratio. The strengthened junction field promotes efficient separation of photogenerated carriers under ultraviolet illumination, increasing the photosensitivity from 10³ to beyond 10⁶ while achieving a responsivity of 80 A/W, a specific detectivity of 0.25 × 10¹² Jones, and an external quantum efficiency of 27200%. This elevated built-in potential further enables zero-biased ultraviolet photodetection with a photosensitivity of ∼10⁴ and a responsivity of 45 mA/W. Furthermore, a three-terminal electrolyte-gated device can demonstrate ion-induced modulation of the interfacial barrier, enabling a transition from rectifying to near-Ohmic behavior and thereby realizing a tuneable diode. This electrolyte-assisted ionic-modulation strategy enables reconfigurable hybrid heterojunctions for next-generation, energy-efficient sensing and multifunctional optoelectronic applications.