Go for gold: As‐prepared insulin–Au nanoclusters (NCs) show intense red fluorescence, excellent biocompatibility, and preservation of natural insulin bioactivity in lowering the blood‐glucose level. Their versatility in applications is demonstrated by fluorescence imaging, X‐ray computed tomography, and insulin–inhibitor interactions (see picture; IDE=insulin‐degrading enzyme).

We report the use of selective wavelength excitation to examine the surface band-bending effects on the optical properties of 3.0-nm-thick indium gallium nitride ͑InGaN͒ multiple quantum wells ͑MQWs͒. Under a 355-nm excitation, the In 0.18 Ga 0.82 N well emission exhibits a linear dependence on the injected carrier density (N inj ) with a coefficient of ͑i͒ 8.5ϫ10 Ϫ18 meV cm 3 for the spectral blueshift and ͑ii͒ 3ϫ10 Ϫ14 V cm 2 for the change of internal field at a density up to N inj ϳ10 19 cm Ϫ3 at 77 K. When excited by a shorter wavelength at 248 nm, the emission from the thin GaN cap layer quenches, but that from the InGaN wells prevails. These observations are attributed to the transportation of photogenerated carriers from the bent GaN surface and redistribution in the InGaN wells. By solving the rate and Poisson equations with a Fermi-level pinning in the band-structure analysis, the emission from the InGaN/GaN MQWs is shown dominant by the recombination between the high-lying subbands and the screening of internal field effects.From recent developments in the material growth and device processing on aluminum indium gallium nitride ͑Al-InGaN͒, this material system has emerged as a promising light source spanning a wide spectral range from ultraviolet to red. 1 Commercialization of candela-class InGaN quantumwell ͑QW͒ blue/green light-emitting diodes, 2 and longlifetime violet and blue laser diodes 3 are examples of such exciting achievements. Despite the progress that has been made in active layer design, 4 many of its peculiar optical properties still remain a great mystery to be solved. 5 A prevailing theory ascribes the emission mechanism to the localized states 6 from the growth of InGaN layer. 7 Alternatively, a characteristic internal field distribution, arisen from the discontinuity of piezoelectricity ( P pz ) and spontaneous polarization ( P sp ) at the nitride interface, 8 can also respond to the change of oscillator strength in spectral analysis. 9 A general assumption is that the recombination is governed by the localized states at low temperature, whereas at high temperature, it is controlled by the extended states. A recent study, 10 however, reveals a drastic reduction in the stability of localized exciton due to the large internal field 11 and carrier screening effects 12 in the InGaN/GaN QW. This makes the treatment of field distribution inside the nitride multiple QWs ͑MQWs͒ an important consideration for the optical analysis. 13 The discontinuity of P sp and P pz at the cap/air interface also imposes a disturbance on the boundary condition. The resultant surface charge, which can be as large as 2ϫ10 13 cm Ϫ2 , constitutes another issue to be resolved in the band-structure analysis. 14 In this letter, we report a series of photoluminescence ͑PL͒ experiments by selective wavelength excitation at vari-ous temperatures to examine the surface band-bending effects on the optical properties of InGaN/GaN MQWs. We find it essential to include a Fermi-level pinning in the GaN cap layer 15 to quant...

We report the Cu + chelated poly-alkoxythiophene (P3MEET) enhancement of a solar cell device consisting of a P3HT/PCBM heterojunction system. Compared to the reference P3HT/PCBM system, a consistent increase of conversion efficiency of 0.9% via an apparent increase of incident-photon-to-current conversion efficiency (IPCE) is achieved upon optimizing the ratio of P3MEET-Cu + : P3HT : PCBM to 1 : 9 : 6 by weight, in which 7.5 mol% of CuBr is added upon synthesizing P3MEET-Cu + . The results, in combination with relevant data gathered from atomic force microscopy, cyclic voltammetry, and electrochemical impedance spectra, lead us to conclude that the match in redox potential and increase of ordering of the film upon doping P3MEET-Cu + play two key roles in enhancing the performance.

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