transforms electrical energy into mole cular hydrogen (H 2 ) and oxygen (O 2 ) that can be reconverted into electrical energy on demand with a fuel cell, represents a leading approach for the scalable long term storage and transport of renewable energy, [4] given the terrestrial abundance of H 2 O. Considering that H 2 is also an essential chemical building block (e.g., for NH 3 production) and can also be converted into liquid fuels with CO 2 using industri ally established transformations (reverse water-gas shift and Fischer-Tropsch), an energy and chemical economy based pri marily on hydrogen produced from solar energy is not only conceivable, but highly anticipated. However, to attain economi callyfeasible solardriven H 2 production at a global scale, challenges remain in the identification of materials and systems that can achieve high solartofuel energy conversion efficiency and robust perfor mance at lowcost. [5] In particular, the development of suitable light harvesting semiconducting materials with ideal properties for solardriven water split ting has been a major focus of research in the past decades. [6] To date, although numerous inorganic semiconductors [7][8][9][10][11][12] have demonstrated solar watersplitting in various device architectures, [13] systems that can produce H 2 at a price competitive with fossil fuel based H 2 production remain elusive. [14] Therefore, a new generation of high performance, stable materials based on earth abundant elements and low cost processing is needed to enable solar water splitting for the glo balized storage of solar energy and a carbonneutral industrial chemical economy.Solutionprocessed organic semiconductors, which con tain an aromatic core of conjugated carbon-carbon bonds, which brings an electronic structure suitable for semicon ducting operation, and flexible appendages (e.g., alkyl groups) to afford solubility in common solvents, represent a promising class of materials to enable lowcost, high performance solar fuel production. Indeed, both conjugated polymers and small molecules have already been wellestablished in organic photo voltaic (OPV) devices. [15][16][17][18][19][20] The solartoelectricity (photovoltaic) power conversion efficiency (η PV ) of stateofthe art OPVs has surpassed 17% by optimization of the organic semiconductor molecular structures and device engineering. [21][22][23][24] Considering the success of solutionprocessable organic semiconductors in OPV, research is now emerging to exploit their advantages over Solution processable organic semiconductors are well-established as highperformance materials for inexpensive and scalable solar energy conversion in organic photovoltaic (OPV) devices, but their promise in the economic conversion of solar energy into chemical energy (solar fuels) has only recently been recognized. Herein, the main approaches employing organic semiconductor-based devices toward solar H 2 generation via water splitting are compared and performance demonstrations are reviewed. OPV-biased water electrolysis is see...

As organic semiconductors attract increasing attention to application in the fields of bioelectronics and artificial photosynthesis, understanding the factors that determine their robust operation in direct contact with aqueous electrolytes becomes a critical task. Herein we uncover critical factors that influence the operational stability of donor:acceptor bulk heterojunction photocathodes for solar hydrogen production and significantly advance their performance under operational conditions. First, using the direct photoelectrochemical reduction of aqueous Eu 3+ and impedance spectroscopy, we determine that replacing the commonly used fullerene-based electron acceptor with a perylene diimide-based polymer drastically increases operational stability and identify that limiting the photogenerated electron accumulation at the organic/water interface to values of ca. 100 nC cm −2 is required for stable operation (>12 h). These insights are extended to solar-driven hydrogen production using MoS 3 , MoP, or RuO 2 water reduction catalyst overlayers where it is found that the catalyst morphology strongly affects performance due to differences in charge extraction. Optimized performance of bulk heterojunction photocathodes coated with a MoS 3 :MoP composite gave 1 Sun photocurrent density up to 8.7 mA cm −2 at 0 V vs RHE (pH 1). However, increased stability was gained with RuO 2 where initial photocurrent density (>8 mA cm −2 ) deceased only 15% or 33% during continuous operation for 8 or 20 h, respectively, thus demonstrating unprecedented robustness without a protection layer. This performance represents a new benchmark for organic semiconductor photocathodes for solar fuel production and advances the understanding of stability criteria for organic semiconductor/water-junction-based devices.

Exfoliated transition metal dichalcogenides (2D-TMDs) are attractive light-harvesting materials for large-area and inexpensive solar energy conversion given their ability to form highly tolerant heterojunctions. However, the preparation of large-area heterojunctions with these materials remains a challenge toward practical devices, and the details of photogenerated charge carrier harvesting are not well established. In this work, we use all solution-based methods to prepare large-area hybrid heterojunction films consisting of exfoliated semiconducting 2H-MoS2 flakes and a perylene-diimide (PDI) derivative. Hybrid photoelectrodes exhibited a 6-fold improvement in photocurrent compared to that of bare MoS2 or PDI films. Kelvin probe force microscopy, X-ray photoelectron spectroscopy, and transient absorption measurements of the hybrid films indicate the formation of an interfacial dipole at the MoS2/organic interface and suggest that the photogenerated holes transfer from MoS2 to the PDI. Moreover, performing the same analysis on MoSe2-based hybrid devices confirms the importance of proper valence band alignment for efficient charge transfer and photogenerated carrier collection in TMD/organic semiconductor hybrid heterojunctions.

Enhancing thermal stability of solution-processed small molecule semiconductor thin films using a flexible linker approach.

Organic field‐effect transistors (OFETs) have shown great promise for use as chemical sensors for applications that range from the monitoring of food spoilage to the determination of air quality and the diagnosis of disease. However, for these devices to be truly useful, they must deliver reliable and stable low‐voltage operation over extended timescales. An important element to address this challenge is the development of a high‐capacitance gate dielectric that delivers excellent insulation with robust chemical resistance against the solution processing of organic semiconductors (OSC). The development of a bilayer gate dielectric containing a high‐k fluoropolymer relaxor ferroelectric layer modified at the OSC/dielectric interface with a photo‐crosslinked chemically resistant low‐k methacrylate‐based copolymer buffer layer is reported. Bottom‐gate OFET chemical sensors using this bilayer dielectric operate at low‐voltage with exceptional operational stability. They deliver reliable sensing performance over multiple cycles of ammonia exposure (2 to 50 ppm) with an estimated limit‐of‐detection below 1 ppm.