Conceptual 2D Ionic Carbon Nitride Photovoltachromic Batteries for Photovoltaic‐Driven Energy Storage and Dynamic Light Management

ABSTRACT Harnessing the trifunctional light‐harvesting, photoelectron‐storage, and photochromic properties of the 2D ionic carbon nitride potassium poly(heptazine imide) (KPHI), this work introduces a ‘photovoltachromic battery’ (PVCB) as a multifunctional device operating under ambient conditions. The PVCB is constructed from a KPHI photoelectrode and a poly(3,4‐ethylenedioxythiophene) electrode, separated by a cobalt‐based redox couple electrolyte. The energy offset between the Fermi level of KPHI and the redox potential of the cobalt couple endows photovoltaic functionality, enabling seamless coupling of photovoltaic‐driven solar energy storage with dynamic light modulation. Acting as a solar battery, the PVCB can harvest and electrochemically store excess solar energy at peak sunlight, subsequently discharging it on demand to maintain a stable electricity supply. Simultaneously, the intrinsic color change associated with photoelectron storage in KPHI, together with photovoltaic regulation via external load tuning, allows precise transparency control. This capability overcomes the passive, weather‐dependent limitation of traditional smart windows and enables system‐level optimization for both energy savings and occupant comfort. By uniting solar energy conversion, storage, and intelligent light management within a single device, PVCBs open a pathway toward next‐generation platforms for building‐integrated and portable applications.