A Push–Pull Type Electron-Selective Self-Assembled Monolayer in Organic Semiconductor Photoanodes for Solar Water Oxidation

Effective charge extraction in organic semiconductor (OS)-based photoelectrochemical (organic PEC) cells is essential for achieving high-performance while mitigating detrimental charge accumulation. Here, we present a series of 1,8-naphthalimide-derived dipolar molecules as standalone electron-selective self-assembled monolayers (SAMs) in organic PEC cells. The dipole moments of these SAM molecules are significantly adjusted to over 5 D via a push–pull molecular design strategy, enabling effective modulation of the work function of the substrates to facilitate selective electron extraction. Furthermore, we demonstrate that modifying the pendant groups on these SAMs tunes the interfacial dipole, thereby governing electron extraction dynamics. Consequently, organic photoanodes based on a thiophene-substituted SAM (NI-T) achieve efficient solar water oxidation with a photocurrent density up to 7.97 mA cm –2 at 1.23 V vs reversible hydrogen electrode (RHE). Our findings highlight the importance of the push–pull design and interfacial dipole orientation in optimizing charge extraction in organic PEC cells.