Currently, photoelectrochemical water‐splitting research is dominated by inorganic and organic–inorganic hybrid photoelectrodes. Although organic semiconductors have several advantages over their inorganic counterparts, the development of photoelectrodes based on pure organic materials has been lagging for the last decade. Recent improvements in molecular design, synthesis, and processing of organic semiconductors, such as polythiophenes, graphitic carbon nitrides, conjugated acetylenic polymers, alternating donor–acceptor‐conjugated polymers, and N‐containing fused‐ring small molecules, significantly enhance the performance of these photolectrodes without added cocatalysts. Although this research has been conducted over the past few years, this overlooked topic still stays unexplored, with more efficient materials yet to be discovered. Herein, the early development and recent advances of exclusively organic photoelectrodes for water splitting are summarized and brief perspectives for future improvements are provided.

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An organic ambipolar transistor allows the integration of p-type and n-type charge carrier transport in a single device. However, the tunability of carrier polarity to meet specific requirements for practical applications is challenging and thus rarely studied. In this work, two dual-acceptor-type polymers (FuI and SeI) based on diketopyrrolopyrrole (DPP) and bithiophene imide (BTI) are reported. By varying the flanking groups of DPP (furan for FuI and selenophene for SeI) and through an ionic additive strategy, the charge carrier polarity of both polymers in organic field-effect transistors (OFETs) can be directionally tuned. Specifically, pristine polymers exhibited an ambipolar property with the μe/μh values of 2.79 for FuI and 4.9 for SeI. Notably, the average electron mobility of SeI reaches as high as 0.122 cm2 V–1 s–1. More encouragingly, with 11.76% tetrabutylammonium iodide (TBAI, mole percentage) as an additive to the FuI polymer, the μe/μh of resultant OFETs varied from 2.79 to 0.71, showing the conversion from n-type dominant to p-type dominant transport. With the same mole percentage of the TBAI to SeI polymer, a dramatic increment of μe/μh from 4.9 to 264 was observed, demonstrating the significant conversion from n-type dominant ambipolar to unipolar n-type transport. Overall, this study demonstrates the possibility of directional tunability of carrier polarity in organic ambipolar transistors with DPP- and BTI-based dual-acceptor polymers through molecular modification and the ionic additive strategy, being significantly beneficial for complementary circuits.

Thiadiazolo[3,benzotriazole (TBZ) and bis(thieno[3,2-b]thiophenyl)ethylene (DTTE)-based conjugated polymers were designed and synthesized by Stille polycondensation, and the effect of the side chain alkyl positions on the optical, electrochemical, and charge-transporting properties in organic field-effect transistors was comprehensively studied. By optimizing the alkyl positions, we obtained semicrystalline polymers, but their hole mobilities were ∼0.1 cm 2 V −1 s −1 due to the face-on dominant orientation. It was also found that the thiophene spacers, which have traditionally been present in the TBZ-based copolymers, are the source of the backbone torsion. Removal of the thiophene units produced an almost planar copolymer backbone with an edge-on and bimodal texture, which exhibited the improved hole mobility exceeding 0.4 cm 2 V −1 s −1 .