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Efficient near-infrared (NIR) photopolymerization is promising for applications such as hydrogel bioprinting, composite manufacturing, and other technologies that benefit from deep light penetration and low-energy activation. Yet, design principles for... 

Proper derivation of CH3NH3PbX3 (CH3NH3+ = methyl ammonium or MA+; X- = Cl-, Br-, I-) optical constants is a critical step toward the development of high-performance electronic and optoelectronic perovskite devices. To date, the optical dispersion regimes at, above, and below the band gap of these materials have been inconsistently characterized by omitting or under-approximating anomalous spectral features (from ultraviolet to infrared wavelengths). In this report, we present the rigorous optical dispersion data analysis of single crystal MAPbBr3 involving variable angle spectroscopic ellipsometry data appended with transmission intensity data. This approach yields a more robust derivation of MAPbBr3 optical constants (refractive index, n, and extinction coefficient, k) for both anomalous (absorptance) and normal (no absorptance) optical dispersion regimes. Using the derived optical constants for our MAPbBr3 single crystals, illustrative modeled solar cell device designs are presented in relation to non-realistic designs prepared using representative optical constants reported in the literature to date. In comparison, our derived optical dispersion data enables the modeled design of realistic planar perovskite solar cell (PSC) optical performance where the active layer (MAPbBr3) is optimized for maximum solar radiation absorption. We further demonstrate optimized modeled planar PSC designs with minimal parasitic optical absorptance in non-active PSC device layers resulting in improved performance at broad angles of incidence (approximately 0-70°). Our robust derivation of MAPbBr3 optical properties is expected to impact the optical dispersion data analysis of all perovskite analogs and expedite targeted development of, for example, solar cell, light-emitting diode, photo and X-ray/γ-ray detector, and laser system technologies. 

A series of thiophene-fused boron dipyrromethene (BODIPY) photoredox catalysts are systematically examined to identify structure–reactivity relationships that enable efficient near-infrared light-induced polymerizations. 

Abstract The use of visible light to drive polymerizations with spatiotemporal control offers a mild alternative to contemporary UV‐light‐based production of soft materials. In this spectral region, photoredox catalysis represents the most efficient polymerization method, yet it relies on the use of heavy‐atoms, such as precious metals or toxic halogens. Herein, spin‐orbit charge transfer intersystem crossing from boron dipyrromethene (BODIPY) dyads bearing twisted aromatic groups is shown to enable efficient visible light polymerizations in the absence of heavy‐atoms. A ≈5–15× increase in polymerization rate and improved photostability was achieved for twisted BODIPYs relative to controls. Furthermore, monomer polarity had a distinct effect on polymerization rate, which was attributed to charge transfer stabilization based on ultrafast transient absorption and phosphorescence spectroscopies. Finally, rapid and high‐resolution 3D printing with a green LED was demonstrated using the present photosystem.