A class of tunable visible and near-infrared donor−acceptor Stenhouse adduct (DASA) photoswitches were efficiently synthesized in two to four steps from commercially available starting materials with minimal purification. Using either Meldrum's or barbituric acid "acceptors" in combination with aniline-based "donors", an absorption range spanning from 450 to 750 nm is obtained. Additionally, photoisomerization results in complete decoloration for all adducts, yielding fully transparent, colorless solutions and films. Detailed investigations using density functional theory, nuclear magnetic resonance, and visible absorption spectroscopies provide valuable insight into the unique structure−property relationships for this novel class of photoswitches. As a final demonstration, selective photochromism is accomplished in a variety of solvents and polymer matrices, a significant advantage for applications of this new generation of DASAs.

A major challenge in organic solar cell design is the trade-off between oxidative stability and work function of the metal cathode. We found that in single-junction polymer solar cells, this problem can be surmounted by solution-based incorporation of fulleropyrrolidines with amine (C60-N) or zwitterionic (C60-SB) substituents as cathode-independent buffer layers. Specifically, a thin layer of C60-N reduced the effective work function of Ag, Cu, and Au electrodes to 3.65 electron volts. Power conversion efficiency values exceeding 8.5% were obtained for organic photovoltaics independent of the cathode selection (Al, Ag, Cu, or Au). Such high efficiencies did not require precise control over interlayer thickness, as devices prepared with C60-N and C60-SB layers ranging from 5 to 55 nanometers performed with high efficiency.

A novel library of tunable negative photochromic compounds, donor-acceptor Stenhouse adducts (DASAs), is reported. Tailoring the electron deficient "acceptor" moiety yielded DASAs that can be activated with mild visible and far red light. The effect of acceptor composition on reactivity, absorption, equilibrium, and cyclability is exploited for the design of high performance photoswitches. The structural changes to the carbon acid acceptor also provide access to new, more structurally diverse DASA derivatives by facilitating the ring-opening reaction with electron deficient amine donors.

We report on the solution-state assembly of all-conjugated polythiophene diblock copolymers containing nonpolar (hexyl) and polar (triethylene glycol) side chains. The polar substituents provide a large contrast in solubility, enabling formation of stably suspended crystalline fibrils even under very poor solvent conditions for the poly(3-hexylthiophene) block. For appropriate block ratios, complexation of the triethylene glycol side chains with added potassium ions drives the formation of helical nanowires that further bundle into superhelical structures.

low exciton binding energy [ 20,21 ] and long carrier diffusion length, [21][22][23] metal halide perovskites with organic counterions have enabled both mesoscopic and planar solar cells to achieve power conversion effi ciencies (PCEs) >18%, [24][25][26][27][28][29] with state-of-theart mesocopic devices reaching a certifi ed PCE of 20.1%. [ 27 ] To date, perovskite solar cells with planar heterojunction structures are slightly less effi cient than their mesoscopic counterparts, but their fabrication is straightforward and compatible with well-established solution-based low temperature fabrication roll-to-roll procedures used for the production of polymer solar cells. [24][25][26][27] The incorporation of charge selective transport layers at the electrode/active layer junctions has often been regarded as a prerequisite to realize effi cient charge extraction in planar perovskite solar cells. [ 30 ] Thus, great effort has been focused on the development and understanding of interfacial engineering between perovskite and electron transport layers (ETLs) or hole transport layers (HTLs) for effective charge carrier separation. [31][32][33][34][35] In perovskite solar cells, the diffusion length of electrons is shorter than holes and it is regarded as a major limitation associated with these devices. [ 36,37 ] To address this limitation, compact semiconducting metal oxide (e.g., ZnO, TiO 2 ) ETLs have been used to facilitate electron transport in planar heterojunction devices. [ 2,14,38,39 ] In addition to the use of metal oxide layers, electrode work function modifi cation by an interlayer can further improve the performance of perovskite solar cells. [ 26,[40][41][42][43][44][45][46][47] For example, Yang et al. incorporated polyethyleneimine ethoxylated (PEIE) between indium tin oxide (ITO) electrode and TiO 2 to signifi cantly increase the PCE of planar heterojunction perovskite solar cells, identifying that reduction of ITO's work function (Φ) by PEIE, due to the presence of a negative interfacial dipole, was a leading contributor to the observed device performance improvement. [ 26 ] Phenyl-C 61 -butyric acid methyl ester (PC 61 BM) has been used as an alternative ETL to metal oxide layers in planar heterojunction devices, providing more effi cient charge injection from perovskite, [ 25 ] while allowing for low-temperature solution processing that precludes ITO's use as an electron-extracting electrode. [ 25,48,49 ] In addition, the deposition of PC 61 BM on perovskite fi lm [ 50 ] or making perovskite-PC 61 BM hybrid active layer [ 51 ] is effective to passivate charge trap states and defects Interface engineering is critical for achieving effi cient solar cells, yet a comprehensive understanding of the interface between a metal electrode and electron transport layer (ETL) is lacking. Here, a signifi cant power conversion effi ciency (PCE) improvement of fullerene/perovskite planar heterojunction solar cells from 7.5% to 15.5% is shown by inserting a fulleropyrrolidine interlayer between the silver electrode an...

A novel methodology for printing 3D objects with spatially resolved mechanical and chemical properties is reported. Photochromic molecules are used to control polymerization through coherent bleaching fronts, providing large depths of cure and rapid build rates without the need for moving parts. The coupling of these photoswitches with resin mixtures containing orthogonal photo-crosslinking systems allows simultaneous and selective curing of multiple networks, providing access to 3D objects with chemically and mechanically distinct domains. The power of this approach is showcased through the one-step fabrication of bioinspired soft joints and mechanically reinforced "brick-and-mortar" structures.

Conjugated polymeric zwitterions, when utilized as interlayer materials in bulk heterojunction organic solar cells, lead to significantly enhanced power conversion efficiencies. The electrostatic model of self-aligning dipolar side groups in the vicinity of the metal surface rationalizes the effects of reduced cathode work function, a key factor behind the observed enhanced efficiency.

Light-driven 3D printing to convert liquid resins into solid objects (i.e., photocuring) has traditionally been dominated by engineering disciplines, yielding the fastest build speeds and highest resolution of any additive manufacturing process. However, the reliance on high-energy UV/violet light limits the materials scope due to degradation and attenuation (e.g., absorption and/or scattering). Chemical innovation to shift the spectrum into more mild and tunable visible wavelengths promises to improve compatibility and expand the repertoire of accessible objects, including those containing biological compounds, nanocomposites, and multimaterial structures. Photochemistry at these longer wavelengths currently suffers from slow reaction times precluding its utility. Herein, novel panchromatic photopolymer resins were developed and applied for the first time to realize rapid high-resolution visible light 3D printing. The combination of electron-deficient and electron-rich coinitiators was critical to overcoming the speed-limited photocuring with visible light. Furthermore, azo-dyes were identified as vital resin components to confine curing to irradiation zones, improving spatial resolution. A unique screening method was used to streamline optimization (e.g., exposure time and azo-dye loading) and correlate resin composition to resolution, cure rate, and mechanical performance. Ultimately, a versatile and general visible-light-based printing method was shown to afford (1) stiff and soft objects with feature sizes <100 μm, (2) build speeds up to 45 mm/h, and (3) mechanical isotropy, rivaling modern UV-based 3D printing technology and providing a foundation from which bio- and composite-printing can emerge.