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Flexible electronics have received considerable attention in the past decades due to their promising application in rollable display screens, wearable devices, implantable devices, and other electronic applications. In particular, conjugated polymers are favored for flexible electronics due to their mechanical flexibility and potential for solution‐processed fabrication techniques, such as blade‐coating, roll‐to‐roll printing, and high‐throughput printing allowing for high‐performance transistor devices. Thiophene is the prevailing conjugated unit to construct these conjugated polymers due to its favorable electronic properties. On the other hand, furans are among the few conjugated moieties that are easily derived from bio renewable resources. To promote sustainability, we selectively introduced furan into the conjugated backbone of a high‐mobility polymer scaffold and systematically studied the effect on the microstructure and charge transport. We show that partially and selectively replacing thiophene units with furan can yield nearly comparable performance compared to the all‐thiophene polymer. This strategy offers an improvement in the sustainability of the polymer by incorporating bio‐sourced furan without sacrificing the high‐performance characteristics. Meanwhile, polymers with incorrect or complete furan incorporation show reduced mobilities. This work serves to develop coherent structure–morphology–performance relationships; such knowledge will establish guidelines for the future development of sustainable, furan‐based conjugated materials.

 

China has made a concerted effort to successfully improve water quality of rivers, but lake water quality has not improved. Lakes require controls on both catchment external nutrient loads and in-lake internal loads, where nature-based solutions are coupled with engineered systems to achieve the United Nations Sustainable Development Goals (SDGs).

 

Understanding chemical degradation at the interface between different layers in an organic photovoltaic device (OPV) is crucial to improving the long‐term stability of OPVs. Herein, molecular‐level insights are provided into the impact of different metal top electrodes on the interfacial morphology and stability of photoactive layers in PM6:Y6 bulk‐heterojunction (BHJ) OPVs. OPVs with an aluminum (Al) top electrode exhibit inferior stability compared to silver (Ag) electrode devices upon thermal annealing, whereby thermal stress induces the diffusion of both Al and Ag atoms to the PM6:Y6 BHJ layer. The diffused Al atoms cause surface recombination at the interface between the photoactive layer and an interlayer. Specifically, X‐ray photoelectron spectroscopy suggests the different local chemical environments of PM6 and Y6 moieties in PM6:Y6/Al‐contact devices. These results are corroborated by solid‐state nuclear magnetic resonance and electron paramagnetic resonance spectroscopy measurements, indicating the formation of ionic and organo‐metallic‐like species at the sub‐layers of the PM6:Y6 BHJ morphology, which are estimated to be less than 5 wt% of the PM6:Y6/Al blend. By comparison, the Ag atoms do not adversely affect PM6:Y6 BHJ morphology and the associated device physics. The investigation of reactive electrode‐BHJ interfaces by multiscale characterization techniques and device physics is expected to provide guidance to future interfacial engineering strategies to develop stable and efficient OPVs.

 

In inorganic materials, an alloy is a mixture of two or more substances that generally exhibits electronic and/or physical properties that differ from those of its constituents. In organic systems, the formation of a “molecular alloy” comprising mixtures of molecular organic materials has also been proposed. We test the validity of this concept via the study of the optoelectronic properties of a ternary system that has previously been identified to form a molecular acceptor alloy, namely a blend of a poly(3-hexylthiophene) (P3HT) donor, with two acceptors indene-C 60 bisadduct (ICBA) and phenyl-C 61 -butyric acid methyl ester (PC 61 BM) [R. A. Street, et al. , J. Am. Chem. Soc. , 2013, 135 , 986–989]. Using photoelectron spectroscopy, we find that the ICBA:PC 61 BM blend shows the same highest occupied molecular orbital and exciton energies as that of ICBA, indicating the absence of a new exciton state in the blend. Furthermore, charge transfer state spectra of ternary blends are found to comprise a simple linear superposition of the corresponding binaries. From these results, no evidence of new, emergent electronic states is found to support the existence of a molecular alloy in this system. To our knowledge there is as yet no clear evidence of the existence of an alloy in any organic semiconductor system. We discuss the criteria that should be met by a molecular organic alloy and procedures needed for their unambiguous identification. 

Orienting light‐emitting molecules relative to the substrate is an effective method to enhance the optical outcoupling of organic light‐emitting devices. Platinum(II) phosphorescent complexes enable facile control of the molecular alignment due to their planar structures. Here, the orientation of Pt(II) complexes during the growth of emissive layers is controlled by two different methods: modifying the molecular structure and using structural templating. Molecules whose structures are modified by adjusting the diketonate ligand of the Pt complex, dibenzo‐(f,h)quinoxaline Pt dipivaloylmethane, (dbx)Pt(dpm), show an ≈20% increased fraction of horizontally aligned transition dipole moments compared to (dbx)Pt(dpm) doped into a 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl, CBP, host. Alternatively, a template composed of highly ordered 3,4,9,10‐perylenetetracarboxylic dianhydride monolayers is predeposited to drive the alignment of a subsequently deposited emissive layer comprising (2,3,7,8,12,13,17,18‐octaethyl)‐21H,23H‐porphyrinplatinum(II) doped into triindolotriazine. This results in a 60% increase in horizontally aligned transition dipole moments compared to the film deposited in the absence of the template. The findings provide a systematic route for controlling molecular alignment during layer growth, and ultimately to increase the optical outcoupling in organic light‐emitting diodes.