High performance inverted bulk heterojunction organic solar cells (OSCs), based on the blend of poly[[4,8-bis[(2-ethylhexyl)oxy] benzo [1,2-b:4,5-b′] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7): 3′H-Cyclopropa[8,25] [5,6]fullerene-C70-D5h(6)-3′-butanoicacid, 3′-phenyl-, methyl ester (PC70BM), were achieved using an aluminum-doped zinc oxide (AZO) front transparent cathode. A structurally identical PTB7:PC70BM-based OSC having an indium tin oxide (ITO) front cathode was also made for comparison studies. The surface of AZO and ITO was modified with a 10 nm thick solution-processed ZnO interlayer to facilitate the efficient electron extraction. This work yielded AZO-based OSCs with a promising power conversion efficiency of 6.15%, slightly lower than 6.57% of a control ITO-based OSC, however, a significant enhancement in the stability of AZO-based OSCs was observed under an ultraviolet (UV)-assisted acceleration aging test. The distinctive enhancement in the lifetime of AZO-based OSCs arises from the tailored absorption of AZO electrode in wavelength <380 nm, serving as a UV filter to inhibit an inevitable degradation in ITO-based OSCs caused by the UV exposure.
Flexible and wearable electronics integrated with various sensors have great potential for applications in monitoring human activities and personal health. Bending and tension/compression dominate the deformation modes yielded by flexure of joints and diverse body gestures. A key challenge now is to sense the curvature/bending angle, while much research has been focused on the strain sensors for tension/compression. Alternative approaches by strain sensors or noncontact optical methods for curvature sensing are not practical for wearable electronics. A novel adhesion‐free thin‐film‐like curvature sensor that can monitor bending activities is introduced for flexible and wearable electronics. This study presents comprehensive design, fabrication, mechanism, structural analysis, performance characterization, and device‐level demonstrations for bending of joints, gesture recognition, and real‐time sitting posture correction. The most prominent advantage of the present sensor is that the measurement is independent of the strain of the target surface and the interfacial slippage, thus the perfect adhesion between the sensor and the surface is unnecessary. The features of adhesion‐free, simple mechanical principle, low cost, and satisfactory monitoring results highlight the superiority of the present curvature sensors for practical applications to flexible and wearable electronics.
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