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The first reduction methodology, compatible with flexible, temperature‐sensitive substrates, for the production of reduced spin‐coated graphene oxide (GO) electrodes is reported. It is based on the use of a laser beam for the in situ, non‐thermal, reduction of spin‐coated GO films on flexible substrates over a large area. The photoreduction process is one‐step, facile, and is rapidly carried out at room temperature in air without affecting the integrity of the graphene lattice or the flexibility of the underlying substrate. Conductive graphene films with a sheet resistance of as low as 700 Ω sq−1 and transmittance of 44% can be obtained, much higher than can be achieved for flexible layers reduced by chemical means. As a proof of concept of our technique, laser‐reduced GO (LrGO) films are utilized as transparent electrodes in flexible, bulk heterojunction, organic photovoltaic (OPV) devices, replacing the traditional ITO. The devices displayed a power‐conversion efficiency of 1.1%, which is the highest reported so far for OPV device incorporating reduced GO as the transparent electrode. The in situ non‐thermal photoreduction of spin‐coated GO films creates a new way to produce flexible functional graphene electrodes for a variety of electronic applications in a process that carries substantial promise for industrial implementation.

Inorganic and organic-inorganic (hybrid) perovskite semiconductor materials have attracted worldwide scientific attention and research effort as the new wonder semiconductor material in optoelectronics. Their excellent physical and electronic properties have been exploited to boost the solar cells efficiency beyond 23% and captivate their potential as competitors to the dominant silicon solar cells technology. However, the fundamental principles in Physics, dictate that an excellent direct band gap material for photovoltaic applications must be also an excellent light emitter candidate. This has been realized for the case of perovskite-based light emitting diodes (LEDs) but much less for the case of the respective laser devices. Here, the strides, exclusively in lasing, made since 2014 are presented for the first time. The solution processability, low temperature crystallization, formation of nearly defect free, nanostructures, the long range ambipolar transport, the direct energy band gap, the high spectral emission tunability over the entire visible spectrum and the almost 100% external luminescence efficiency show perovskite semiconductors’ potential to transform the nanophotonics sector. The operational principles, the various adopted material and laser configurations along the future challenges are reviewed and presented in this paper.

The effect of embedding uncapped Au nanoparticles, produced by ultrafast laser ablation in liquids, in the active layer of bulk heterojunction organic photovoltaic devices was systematically studied. The nanoparticles incorporation leads to a power conversion efficiency improvement of 40%. This efficiency gain was attributed to enhanced light harvesting and subsequent exciton generation rate into the photoactive layer due to localized surface plasmon resonance and scattering effects. This argument was supported by the combinatorial study of spectroscopic analysis and photon to-electron conversion efficiency measurements of the devices.

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wileyonlinelibrary.comtechnologies, [ 1 ] in preparing effi cient, fl exible, transparent, light-weight, large-area, and low-cost devices. [2][3][4] To date, power conversion effi ciencies (PCE) of BHJ OSCs based on polymer and fullerene derivatives are around 10% [ 5,6 ] mainly due to advances on the rational design of lowbandgap polymers, fi ne control of the photoactive layer's nanomorphology and by interface engineering. [ 7 ] However, further improvements in the performance of BHJ solar cells can be foreseen only if many limiting factors, such as insuffi cient light absorption, nonoptimized morphologies, and low charge carrier mobilities of the active layer materials [ 8 ] will be addressed and optimized.The most successful development of OSCs over the last decade is based on the binary BHJ concept, [ 9 ] where a polymer donor and a fullerene acceptor are blended on a nanometer scale. [ 9 ] The polymer (i.e., the donor) should exhibit strong and broad absorption band in visible and near infrared regions as long as high hole mobility to transport carriers effectively toward the anode, while the fullerene (i.e., the acceptor) should have higher lowest unoccupied molecular orbital (LUMO) than the polymer, coupled with high electron mobility. [ 10 ] In terms of OSC optimization, a simple approach relies on the decrease Functionalized graphene nanofl akes (GNFs) are used as an electron-cascade acceptor material in air-processed organic ternary bulk heterojunction solar cells. The functionalization is realized via the attachment of the ethylenedinitrobenzoyl (EDNB) molecule to the GNFs. Simulation and experimental results show that such nanoscale modifi cation greatly infl uences the density of states near the Fermi level. Consequently, the GNF-EDNB blend presents favorable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels to function as a bridge structure between the poly[ N -9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′benzothiadiazole)] (PCDTBT) and the [6,6]-phenyl-C71-butyric-acid-methylester (PC 71 BM). The improved exciton dissociation and charge transport are associated with the better energy level alignment of the ternary blend and the high electrical conductivity of the GNFs, which act as additional electron transport channels within the photoactive layer. The resulting PCDTBT/GNF-EDNB/PC 71 BM ternary organic solar cells, fabricated entirely under ambient conditions, exhibit an average power conversion effi ciency enhancement of ≈18% as compared with the binary blend PCDTBT/PC 71 BM.

An alternating phenylenevinylene copolymer P bearing perylene bisimide moieties along the backbone was synthesized by Heck coupling. The tert-butyl and hexyloxy side groups enhanced the solubility of the copolymer in common organic solvents. It had glass transition and decomposition temperatures of 72 and 370 °C, respectively. The absorption of P was broad, with longer wavelength maximum around 500 nm and optical band gap of 1.66 eV. The solution of P emitted yellow−orange light with photoluminescence (PL) maximum at 555 nm. Moreover, efficient interaction and charge/energy transfer between the phenylenevinylene−donor and the perylene bisimide−acceptor led to PL quenching in the thin film of P. The current−voltage characteristics of ITO/copolymer P/Al indicated that copolymer P behaved as an n type organic semiconductor. The electron current was found to be a space charge limited current (SCLC), providing a direct measure of mobility as a function of temperature and field. The average electron mobility for this copolymer was 0.85 × 10−2 cm2/Vs. The photogeneration mechanism in blends of copolymer P (electron acceptor) with poly(3-phenyl hydrazone thiophene) (PPHT) (electron donor) were investigated. Annealing of the complete device was found to result in an increase in power conversion efficiency from 1.67% to 2.32%. By studying the dependence of photocurrent on effective bias voltage, annealing was found to increase the charge generation efficiency through an increase in the efficiency of separation of exciton following the charge transfer.