Solvent and electric field dependence of the photocurrent generation in donor：acceptor blend system

This paper reports that the blend films of poly （2-methoxy-5-（2＇-ethyl-hexyloxy）-p-phenylene vinylene） （MEH-PPV） and N,N＇-bis（1-ethylpropyl）-3,4： 9,10-perylene bis （tetracarboxyl diimide） （EP-PDI） with the weight ratio of 1：2.5 have been prepared by spin-coating from chloroform （CF） and chlorobenzene （CB） solutions respectively. The absorption spectra and the morphology of the blend films show that large crystal-like EP-PDI aggregates are formed in film prepared from CB solution, which corresponds to a new absorption shoulder near 590 nm, while there is no shoulder around 590 nm in the UV-Vis absorption spectra of the blend film from CF solution. The electric-field dependence spectra of the photocurrent generation quantum yield of the film from CB solution shows that at weak electric field the EP-PDI aggregates act as more efficient sensitizers, but at strong electric field the quantum yields become almost invariable over the entire spectral range no matter what the state of EP-PDI, monomer or aggregate. At strong electric field, the photocurrent generation yields of both films from CF and CB solution saturate and their yield spectra become spectrally similar, mentioning that at strong electric field the photoexcitons dissociate efficiently and the free charges are collected by the electrodes almost completely.

Enhancement of Photocurrent Generation of a Novel Stilbazolium Dye Dimer in LB Monolayer Films

A novel dye dimer, bis-{[1-(N-hexadecyl-4-pyridinium)-2-(4-N, N-dimethylamino- phenyl)] ethenyl}methane diiodide (C16BP) was synthesized, and the photoelectrochemistry of the dye Langmuir-Blodgett monolayer modified ITO electrode was investigated. For comparison, the photoelectrochemistry of the monomer (E)-N-hexadecyl-4-[2-(4-N, N-dimethylaminophenyl) ethenyl] pyridinium iodide (C16P) was also measured. The results show that the photocurrent generation property of the dimer is enhanced. The photocurrent generation quantum yield is 0.38% for C16BP, while that for C16P is 0.23%.

Enhanced Photocurrent Generation of Graphene/Au@ZnO Honeycomb Film

A bio-inspired graphene/Au@ZnO photoelectrode has been prepared via breath figure method, in which Au@ZnO nanospheres were uniformly distributed in the whole honeycomb film. The size of the honeycomb holes effects the light using efficiency. The honeycomb film with smaller holes in more ordered array shows better antire- flective property. All the formed graphene/Au@ZnO honeycomb photoelectrodes show a fast, stable, and reversible response of photocurrent accompanied by each switch-on and switch-off event. Au@ZnO-modified graphene hon- eycomb film can combine the advantages of increased light harvesting provided by honeycomb structure, efficient charge separation from Au nanoparticles （NPs）, and efficient electron transfer provided by graphene. Au@ZnO- modified graphene honeycomb film shows a two-fold increase of photocurrent generation than ZnO-modified gra- phene honeycomb film and a three-fold increase of photocurrent generation than Au@ZnO-modified graphene smooth film, respectively. The rational design and engineering of multi components with different functions in a hybrid bio-inspired structure hold great promise for further efficient solar energy conversion devices.

Multifunctional Molecular Material Combining Photocurrent Generation and Second-Order Optical Nonlinearity in LB Monolayer Films

A novel amphiphilic stilbazolium dye, (E)-N-methyl-4-[2-(4-N-methyl-N-hexadecylaminophenyl) ethenyl]-2-isoquinolinium iodide (MHIQ), was synthesized. The dye was successfully transferred onto ITO electrode or quartz by the Langmuir-Blodgett (LB) technique. The second harmonic generation (SHG) and photocurrent generation properties of the LB film transferred under 35 mN/m of surface pressure were investigated. The broad absorption maximum of the LB monolayer of MHIQ at 434 nm is far away from the wavelength (532 nm) of resonant enhancement effect, and its second harmonic susceptibility x(2) is 167 pm/V, which means that the isoquinolinium is a good electron-accepting group. The photocurrent generation experiment shows that the photocurrent generation properties are dependent on the experimental conditions including bias voltage, redox couples and light intensity. By a light irradiation at 440 nm, the photocurrent generation quantum yields of the dye LB monolayer are 0.50% in 0.5 mol/L KG electrolyte solution and 17.5% in 0.1 mol/L KI electrolyte solution with 0.01 mol/L I2, respectively, indicating that the dye MHIQ is a good photoelectric conversion material.

Graphene-based heterojunction for enhanced photodetectors

Graphene has high light transmittance of 97.7% and ultrafast carrier mobility, which means it has attracted widespread attention in two-dimensional materials. However, the optical absorptivity of single-layer graphene is only 2.3%, and the corresponding photoresponsivity is difficult to produce at normal light irradiation. And the low on–off ratio resulting from the zero bandgap makes it unsuitable for many electronic devices, hindering potential development. The graphene-based heterojunction composed of graphene and other materials has outstanding optical and electrical properties, which can mutually modify the defects of both the graphene and material making it then suitable for optoelectronic devices. In this review,the advantages of graphene-based heterojunctions in the enhancement of the performance of photodetectors are reviewed.Firstly, we focus on the photocurrent generation mechanism of a graphene-based heterojunction photodetector, especially photovoltaic, photoconduction and photogating effects. Secondly, the classification of graphene-based heterojunctions in different directions is summarized. Meanwhile, the latest research progress of graphene-transition metal dichalcogenide(TMD) heterojunction photodetectors with excellent performance in graphene-based heterostructures is introduced. Finally,the difficulties faced by the existing technologies of graphene-based photodetectors are discussed, and further prospects are proposed.

Surface plasmon excitation in semitransparent inverted polymer photovoltaic devices and their applications as label-free optical sensors

Herein,we report on surface plasmon(SP)-sensitive semitransparent inverted polymer photovoltaic(PV)devices that are based on multilayered material systems consisting of poly(3-hexylthiophene):fullerene-derivative bulk-heterojunction PV layers and thin gold or silver anodes.We demonstrate that these PV devices allow the simultaneous generation of both electrical power and SPs on their anodes for photoexcitation just above the optical absorption edge of the PV layers,resulting not only in attenuated total reflection,but also in attenuated photocurrent generation(APG)under the SP resonance(SPR)condition.Moreover,we also confirm that the biomolecular interaction of biotin–streptavidin on the PV devices can be precisely detected via apparent SPR angle shifts in the APG spectra,even without the need for complex attenuated total reflection configurations.We highlight our view that APG measurements made using these PV devices show great potential for the development of future generations of compact and highly sensitive SPR-based optical sensors.