Gate‐Like Chemical Modulation of CdTe via Interfacial Charge Transfer for Enhanced Carrier Mobility

We introduce a (CTC)‐mediated, gate‐like chemical modulation strategy that overcomes poor thickness control and transport‐limiting insulating interlayers in conventional organic surface engineering, while simultaneously enhancing carrier mobility and photoresponse. Beyond defect passivation, the interfacial CTC serves as a chemical gate that mimics field‐effect–like charge modulation, enabling photoinduced interfacial charge separation and generating charge‐separated states that contribute to charge transport and interfacial photoconversion. This strategy is applied to cadmium telluride (CdTe) by self‐assembling viologen acceptors to form a sub‐nanometer interfacial CTC. The resulting CTC functions as a chemical gate, inducing surface electron accumulation with concomitant near‐surface bulk depletion through dipole‐induced band bending, without introducing resistive interlayers; Coulomb coupling further stabilizes the interface while preserving efficient transport. As a result, CdTe exhibits > 60% mobility enhancement, ∼100‐fold conductivity increase, and > 500% improvement in AM 1.5G photoresponse, together with an absorption‐edge extension from ∼1000 to ∼1400 nm, and an ∼37% enhancement in X‐ray photocurrent response. Despite its molecular‐scale thickness, the CTC interface induces a macroscopic reconfiguration of near‐surface charge transport. This solution‐processed, self‐limiting CTC interface provides a manufacturable molecular‐level route for chemical gating of semiconductors, offering a materials‐agnostic strategy compatible with existing doping and strain engineering.