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Two new random donor-acceptor (D-A) copolymers, signed as P1 and P2, were designed and synthesized. Electrochemical and spectroelectrochemical measurements were performed to investigate absorption, energy levels, electronic and optical band gaps for comparison. The polymers were used as donor polymers in the active layer to fabricate non-fullerene, bulk heterojunction (BHJ) organic photovoltaics (OPVs). Investigations were carried out through the conventional BHJ structure; ITO/PEDOT: PSS/Active Layer/LiF/Al, where active layer consists of 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC) as the acceptor and thienopyrroledione containing donors. The device based on P1:ITIC(1:1) blend with a thickness of 161 nm gave the best performance with a power conversion efficiency (PCE) of 7.94%, an open-circuit voltage (V-OC) of 0.86 V, a short-current density (J(SC)) of 18.45 mA cm(-2) and a fill factor (FF) of 50.12%. The highest PCE obtained from P2 based organic solar cell is 1.96%. P2 exhibited low solubility attributed to the lack of alkyl groups enhancing polymer solubility, electronic properties, and photovoltaic performances. The research outputs exhibit that introduction of alkyl chains on the polymer backbone can enhance device performance. (C) 2021 Elsevier Ltd. All rights reserved.

Graphene is conceivably the most nonlinear optoelectronic material we know. Its nonlinear optical coefficients in the terahertz frequency range surpass those of other materials by many orders of magnitude. Here, we show that the terahertz nonlinearity of graphene, both for ultrashort single-cycle and quasi-monochromatic multicycle input terahertz signals, can be efficiently controlled using electrical gating, with gating voltages as low as a few volts. For example, optimal electrical gating enhances the power conversion efficiency in terahertz third-harmonic generation in graphene by about two orders of magnitude. Our experimental results are in quantitative agreement with a physical model of the graphene nonlinearity, describing the time-dependent thermodynamic balance maintained within the electronic population of graphene during interaction with ultrafast electric fields. Our results can serve as a basis for straightforward and accurate design of devices and applications for efficient electronic signal processing in graphene at ultrahigh frequencies., D.T. and H.A.H. acknowledge funding from the European Union’s Horizon 2020 Framework Programme under grant agreement no. 964735 (EXTREME-IR). M.G. and B.G. acknowledge support from the European Cluster of Advanced Laser Light Sources (EUCALL) project that has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 654220. K.-J.T. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 804349 (ERC StG CUHL) and financial support through the MAINZ Visiting Professorship. ICN2 was supported by the Severo Ochoa program from Spanish MINECO (grant no. SEV-2017-0706). Parts of this research were carried out at ELBE at the Helmholtz-Zentrum Dresden-Rossendorf e.V., a member of the Helmholtz Association. F.H.L.K. acknowledges support from the Government of Spain (FIS2016-81044; Severo Ochoa CEX2019-000910-S), Fundació Cellex, Fundació Mir-Puig, and Generalitat de Catalunya (CERCA, AGAUR, and SGR 1656). Furthermore, the research leading to these results has received funding from the European Union’s Horizon 2020 under grant agreement no. 881603 (Graphene Flagship Core 3).

The limited light absorption capacity for most polymer acceptors hinders the improvement of the power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs). Herein, by simultaneously increasing the conjugation of the acceptor unit and enhancing the electron-donating ability of the donor unit, a novel narrow-bandgap polymer acceptor PF3-DTCO based on an A–D–A-structured acceptor unit ITIC16 and a carbon–oxygen (C–O)-bridged donor unit DTCO is developed. The extended conjugation of the acceptor units from IDIC16 to ITIC16 results in a red-shifted absorption spectrum and improved absorption coefficient without significant reduction of the lowest unoccupied molecular orbital energy level. Moreover, in addition to further broadening the absorption spectrum by the enhanced intramolecular charge transfer effect, the introduction of C–O bridges into the donor unit improves the absorption coefficient and electron mobility, as well as optimizes the morphology and molecular order of active layers. As a result, the PF3-DTCO achieves a higher PCE of 10.13% with a higher short-circuit current density (Jsc) of 15.75 mA cm−2 in all-PSCs compared with its original polymer acceptor PF2-DTC (PCE = 8.95% and Jsc = 13.82 mA cm−2). Herein, a promising method is provided to construct high-performance polymer acceptors with excellent optical absorption for efficient all-PSCs.

In the last decade, lead triiodide perovskite (APbI3) (A: organic cation) solar cells (PSCs) have been broadly studied due to their promising features related to the low cost, easy manufacturing process, and stability. Strategies to improve the device stability include the application of techniques such as compositional engineering of the cation of these halide perovskites, but it is still a complex task to find the right balance between the stability and power conversion efficiency of materials and complete devices. In this work, we performed a combined study of five samples of [5-AVA(1−x)MAx]PbI3 (5-AVA: ammonium valeric acid and MA: methylammonium) with x = 1.0, 0.75, 0.5, 0.25 and 0.0, using X-ray diffraction (XRD) and UV-VIS spectroscopy measurements in combination with periodic density functional theory (DFT) based calculations. Our samples showed an optical bandgap of 1.58 eV and the coexistence of the two phases as observed by XRD analyses. The theoretical results of the bandgaps for the no mixed phases (x = 1.0 and x = 0.0) show good agreement with the experiment, obtaining bandgap values overestimated by 0.18 eV and 0.33 eV, respectively. A direct relation between the number of 5-AVA ions in the samples and the stability of the phases was theoretically found and proved through the increment observed in the bandgap and the cohesive energy. We proposed a compositional strategy for perovskites [5-AVA(1−x)MAx]PbI3 with x values of at most 0.5, based on the small blue-shift and the low absorbance reduction of the spectrum curve, added to the small phase stabilization found., We are thankful for the financial support from USACH under the Project POSTDOC_DICYT, Código 021941CJ_POSTDOC (R. U.-L. and G. C.-J.) Powered@NLHPC. This research was partially supported by the supercomputing infrastructure of the NLHPC (ECM-02) of the Universidad de Chile. M. L. C. and H. X. acknowledge the support from Spanish MINECO for grants ENE2016-79282-C5-2-R and PID2019-104272RB-C54, the OrgEnergy Excellence Network CTQ2016-81911-REDT, the Agència de Gestiód'Ajuts Universitaris i de Recerca (AGAUR) for the support to the consolidated Catalonia research group 2017 SGR 329 and the Xarxa de Referència en Materials Avançats per a l'Energia (Xarmae). ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya.

© 2018 The Royal Society of Chemistry. Thin film perovskite photovoltaic devices combine high power conversion efficiencies with low weight, large area, high speed production capabilities and high versatility in form factor. With this paper, an additional feature is added to the device property portfolio: optical transparency. Results on translucent perovskite modules with selectively tuned levels of transparency are reported by applying the industrially established fabrication process of partial area ablation to high efficiency opaque devices. After process completion, the final devices consist of opaque areas that absorb the light, and transparent areas that permit neutral light transmission. We compare the effectiveness of using two active area removal techniques: mechanical scribing and laser ablation, and determine the factors that limit the maximum transparency and power conversion efficiency. Moreover, we show how the choice of the ablation method and design of the active area removal pattern affect and limit the maximum light utilization efficiency ratio that can be achieved with this fabrication process. The resulting 4 cm2 translucent modules cover a range of visible light transparency from 7 to 37% with a corresponding power conversion efficiency of 5 to 13%. ispartof: JOURNAL OF MATERIALS CHEMISTRY C vol:6 issue:12 pages:3034-3041 status: published

Nanocomposite photoanodes were prepared by addition of graphene (GR) micro-platelets to TiO2 nanoparticulate paste. TiO2/graphene based DSSCs were fabricated using Z907 photosensitizer. Transmission electron microscope was used to confirm the presence of graphene in composite films after heating at 450 �C for 30 min. UV-visible absorption spectroscopy, photocurrent-voltage characteristics and electrochemical impedance spectroscopic measurements were conducted to characterize the DSSCs. The results show that the photo conversion efficiency is highly dependent on the concentration of graphene in the photoanode. Under an optimal conditions, solar cell based on graphene/TiO2 shows power conversion efficiency (PCE) of 4.03%, which is about 26% greater than the cell based on pristine TiO2 electrode (3.20%). A density functional theory was used to compute the band gap of TiO2 and graphene-TiO2 nano clusters. The authors would like to acknowledge the support provided by King Abdulaziz City for Science and Technology (KACST) through the Science & Technology Unit at King Fahd University of Petroleum & Minerals (KFUPM) for funding this work through project no. 11-ENE1635-04 as part of the National Science, Technology and Innovation Plan. KFUPM is also acknowledged for supporting this research. The authors would like to acknowledge the Center of Research Excellence for Renewable Energy at KFUPM. Scopus

The optical, electrochemical, morphological and transport properties of a series of thiadiazinone (acceptor) and (thienyl)carbazoles (donor) containing π-extended donor-acceptor-donors (D-A-D) are presented. Systematic variations in the number of the thienyl units, the choice of branched or straight alkyl side chains and the use of a processing additive demonstrate their use as electron donors in bulk heterojunction solar cells blended with fullerene acceptors. The best power conversion efficiency (PCE) of 2.7% is achieved by adding to the D-A-D 3:fullerene blend a polydimethylsiloxane (PDMS) additive, that improves the morphology and doubles the hole mobility within the D-A-D:fullerene blend. © The Royal Society of Chemistry. 3 10 2358 2365 Cited By :7

The nature and dynamics of acceptor states in solution-processed Cu2ZnSn(S,Se)4 (CZTSSe) thin films are investigated by variable temperature photoluminescence (PL) and electrical impedance spectroscopy. Highly pure I-4 phase CZTSSe with the composition Cu1.6ZnSn0.9(S0.23Se0.77)4 is synthesized by sequentially spin coating of dimethyl-formamide/isopropanol solutions containing metal salts and thiourea onto Mo coated glass, followed by annealing in an Se atmosphere at 540 °C. As-annealed films are highly compact with a thickness of 1.3 μm and grain sizes above 800 nm, with a band gap of 1.18 eV. Photovoltaic devices of 0.25 cm2 with the architecture glass/Mo/CZTSSe/CdS/i-ZnO/Al:ZnO demonstrate a power conversion efficiency reaching up to 5.7% in the absence of an anti-reflective coating. Under AM 1.5G illumination at 296 K, the best device shows a 396 mV open-circuit voltage (VOC), 27.8 mA cm-2 short-circuit current (JSC) and 52% fill factor (FF). The overall dispersion of these parameters is under 15% for a total of 20 devices. In the near IR region, PL spectra are dominated by two broad and asymmetrical bands at 1.14 eV (PL1) and 0.95 eV (PL2) with characteristic power and temperature dependences. Analysis of the device electrical impedance spectra also reveals two electron acceptor states with the same activation energy as those observed by PL. This allows assigning PL1 as a radiative recombination at localized copper vacancies (VCu), while PL2 is associated with CuZn antisites, broadened by potential fluctuations (band tails). The impact of these states on device performance as well as other parameters, such as barrier collection heights introduced by partial selenization of the back contact, are discussed. © 2017 The Royal Society of Chemistry. Engineering and Physical Sciences Research Council, EPSRC: EP/L017792/1 Institute of Advanced Studies, University of Bristol, IAS: EP/K035746/1 DT, JWB and DJF are indebted to the Engineering and Physical Sciences Research Council (EPSRC) funded PVTEAM grant (EP/L017792/1). DJF acknowledges Institute of Advanced Studies of the University of Bristol support of a University Research Fellowship 2016. Impedance analysis was performed with a Solartron analyzer procured under EPSRC CDT Capital grant EP/K035746/1. Microscopic imaging and analysis were done at the Chemical Imaging Facility, University of Bristol, with equipment funded by EPSRC Grant ‘‘Atoms to Applications’’ (EP/K035746/1). The authors are grateful for measurement facilities provided at CREST, Loughborough University and the Department of Physics, SUPA, Strathclyde University.

A new tetracyclic lactam building block for polymer semiconductors is reported that was designed to combine the many favorable properties that larger fused and/or amide-containing building blocks can induce, including improved solid-state packing, high charge carrier mobility, and improved charge separation. Copolymerization with thiophene resulted in a semicrystalline conjugated polymer, PTNT, with a broad bandgap of 2.2 eV. Grazing incidence wide-angle X-ray scattering of PTNT thin films revealed a strong tendency for face-on π- stacking of the polymer backbone, which was retained in PTNT:fullerene blends. Corresponding solar cells featured a high open-circuit voltage of 0.9 V, a fill factor around 0.6, and a power conversion efficiency as high as 5% for >200 nm thick active layers, regardless of variations in blend stoichiometry and nanostructure. Moreover, efficiencies of >4% could be retained when thick active layers of ∼400 nm were employed. Overall, these values are the highest reported for a conjugated polymer with such a broad bandgap and are unprecedented in materials for tandem and particularly ternary blend photovoltaics. Hence, the newly developed tetracyclic lactam unit has significant potential as a conjugated building block in future organic electronic materials. Refereed/Peer-reviewed

A series of alternating oligothiophene (nT)–isoindigo (I) copolymers (PnTI) were synthesized to investigate the influence of the oligothiophene block length on the photovoltaic (PV) properties of PnTI:PCBM bulk-heterojunction blends. Our study indicates that the number of thiophene rings (n) in the repeating unit alters both polymer crystallinity and polymer–fullerene interfacial energetics, which results in a decreasing open-circuit voltage (Voc) of the solar cells with increasing n. The short-circuit current density (Jsc) of P1TI:PCBM devices is limited by the absence of a significant driving force for electron transfer. Instead, blends based on P5TI and P6TI feature large polymer domains, which limit charge generation and thus Jsc. The best PV performance with a power conversion efficiency of up to 6.9% was achieved with devices based on P3TI, where a combination of a favorable morphology and an optimal interfacial energy level offset ensures efficient exciton separation and charge generation. The structure–property relationship demonstrated in this work would be a valuable guideline for the design of high performance polymers with small energy losses during the charge generation process, allowing for the fabrication of efficient solar cells that combine a minimal loss in Voc with a high Jsc. Refereed/Peer-reviewed

Research into organic photovoltaics (OPVs) is rapidly growing worldwide because it offers a route to low temperature, inexpensive processing of lightweight, flexible solar cells that can be mass manufactured cheaply. Unlike silicon or other inorganic semiconductors (e.g., CdTe, CIGs), OPVs are complicated by the requirement of having multiple materials and layers that must be integrated to enable the cell to function. The enormous number of research hours required to optimize all aspects of OPVs and to integrate them successfully is typically boiled down to one number-the power conversion efficiency (PCE) of the device. The PCE is the value by which comparisons are routinely made when modifications are made to devices; new bulk heterojunction materials, electron- and hole-transport layers, electrodes, plasmonic additives, and many other new advances are incorporated into OPV devices and compared with one, or a series of, control device(s). The concern relates to the statistical significance of this all-important efficiency/PCE value: is the observed change or improvement in performance truly greater than experimental error? If it is not, then the field can and will be misled by improper reporting of efficiencies, and future research in OPVs could be frustrated and, ultimately, irreversibly damaged. In this Perspective, the dangers of, for instance, cherry-picking of data and poor descriptions of experimental procedures, are outlined, followed by a discussion of a real data set of OPV devices, and how a simple and easy statistical treatment can help to distinguish between results that are indistinguishable experimentally, and those that do appear to be different. © 2013 American Chemical Society.

A novel counter electrode material for dye sensitized solar cells (DSSCs) composed of nanostructured Au particles decorated on functionalized multi-walled carbon nanotubes (f-MWNTs) is demonstrated for the first time. MWNTs synthesized by catalytic chemical vapor deposition technique are purified and functionalized by treating with concentrated acids. Au nanoparticles are decorated on f-MWNTs by a rapid and facile microwave assisted polyol reduction method. The materials are characterized by X-ray diffractometry, Fourier transform infra red spectroscopy and electron microscopy. The DSSC fabricated with Au/f-MWNTs based counter electrode shows enhanced power conversion efficiency (?) of 4.9% under AM 1.5G simulated solar radiation. In comparison, the reference DSSCs fabricated with f-MWNTs and Pt counter electrodes show? of 2.1% and 4.5%. This high performance of Au/f-MWNTs counter electrode is investigated using electrochemical impedance spectroscopy and cyclic voltammetry studies. Copyright � 2012 American Scientific Publishers.

Perovskite solar cells (PSCs) are evolving with an impressive pace, emerging as the most promising next-generation photovoltaic devices. Nevertheless, beside these enormous progresses, the stability of PSCs remains one of the major problems to be challenged, because the most commonly used hole transporting material (HTM), the 2,2′,7,7′-Tetrakis-(N,N-di-4-methoxyphenylamino)−9,9′-spirobifluorene (Spiro-OMeTAD), suffers long-term stability. Here, we tackle this long-lasting issue exploiting reduced graphene oxide (RGO), prepared by an easy and efficient reduction method, as HTM in PSCs. We carried out endurance tests over 1987 h of shelf life and 120 h of light soaking. The PSCs based on RGO have shown power conversion efficiency (PCE) of 6.6%, outperforming the ones achieved with the Spiro-OMeTAD (PCE=6.5%), after the shelf life test. The light soaking test confirmed the better durability of RGO-based PSCs with respect to the Spiro-OMeTAD ones, the latter showing a reduction in PCE 2.7 times higher than the RGO-based cells. Moreover, we demonstrate by Open Circuit Voltage Decay measurements that RGO, beside the HTM function, acts also as an anti-recombination layer, reducing the charge carriers recombination pathways and, hence, increasing their lifetime.

We report the synthesis of new push-pull conjugated polymers for bulk heterojunction solar cells based on benzo[1,2-b:4,5-b′]dithiophene (push) and thieno[3,4-d]thiazole (TTz) (pull) derivatives. Stille polycondensation between distannyl-BDT derivatives with 4,6-dibromo-2-octylthieno[3,4-d]thiazole led to two alternating copolymers, namely PBDTTTz-1 and PBDTTTz-2, which have a bandgap of 1.8 and 1.7 eV, respectively. Both copolymers are stable in air with HOMO energy level of -5.3 eV for PBDTTTz-1 and -5.4 eV for PBDTTTz-2. Both copolymers have been tested in bulk heterojunction solar cells, and preliminary results (without any optimization process) show promising power conversion efficiency of 1.4% for PBDTTTz-1 and 1.7% for PBDTTTz-2. © 2011 American Chemical Society.

Polymer solar cells based on the polyfluorene copolymer poly[9,9-didecanefluorene-alt-(bis-thienylene) benzothiadiazole] (PF10TBT) and the fullerene derivative [6,6]-phenyl C(61)-butyric acid methyl ester (PCBM) exhibit a power conversion efficiency of 4%. However, the optimum thickness of the photoactive layer is only 80 nm, such that these solar cells absorb only half of the photons available in their absorption bandwidth. Thicker cells are subject to electronic losses due to space charge effects and recombination. We demonstrate both from simulations and experiments that the optical and electronic losses can be decoupled in a double junction solar cell. For the PF10TBT: PCBM blend, the integration of two thin cells in a double junction device leads to an enhancement of the measured power conversion efficiency with 13% up to a value of 4.5%. (C) 2010 Elsevier B.V. All rights reserved.

Date of Conference: 9-13 August 2015 Conference name: SPIE Optics + Photonics for Sustainable Energy, 2015 - Proceedings - Thin Films for Solar and Energy Technology VII Recent studies in monocrystalline semiconductor solar cells are focused on mechanically stacking multiple cells from different materials to increase the power conversion efficiency. Although, the results show promising increase in the device performance, the cost remains as the main drawback. In this study, we calculated the theoretical limits of multistacked 1D and 2D microstructered inorganic monocrstalline solar cells. This system is studied for Si and Ge material pair. The results show promising improvements in the surface reflection due to enhanced light trapping caused by photon-microstructures interactions. The theoretical results are also supported with surface reflection and angular dependent power conversion efficiency measurements of 2D axial microwall solar cells. We address the challenge of cost reduction by proposing to use our recently reported mass-manufacturable fracture-transfer- printing method which enables the use of a monocrystalline substrate wafer for repeated fabrication of devices by consuming only few microns of materials in each layer of devices. We calculated thickness dependent power conversion efficiencies of multistacked Si/Ge microstructured solar cells and found the power conversion efficiency to saturate at %26 with a combined device thickness of 30 μm. Besides having benefits of fabricating low-cost, light weight, flexible, semi-transparent, and highly efficient devices, the proposed fabrication method is applicable for other III-V materials and compounds to further increase the power conversion efficiency above 35% range. © 2015 SPIE.

Sn doped β-Ga2O3 nanowires have been grown on Si(001) via the vapor-liquid-solid mechanism at 800 °C over a broad range of compositions. These have a monoclinic β-Ga2O3 crystal structure and minimum resistances for 1-2 at. % Sn but we observe the emergence of tetragonal rutile SnO2 which dominates with increasing content of Sn. All of the nanowires exhibited photoluminescence at 2.7 eV but a red shift of the emission occurred from 2.7 eV to 1.8 eV after post growth processing under H2S above 500 °C. The red emission is related to deep donor to acceptor transitions and the formation of monoclinic β-Ga2S3 and has been exploited for spectral shifting in a Si solar cell resulting into an increase of the power conversion efficiency from 7.2% to 8.3%. © 2015 AIP Publishing LLC. 118 19 Cited By :1

We report the processing conditions for inkjet-printed active layers of organic photovoltaic (OPV) devices comprising bulk-heterojunction blends of the low bandgap conjugated polymer poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b: 2′,3′-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1, 3-benzothiadiazole)-5,5′-diyl] (Si-PCPDTBT) as well as poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′, 7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) used as electron donors with [6,6]-phenyl-C71-butyric acid methyl ester (PC 70BM) as electron acceptor. By controlling the inkjet printing processing conditions, we gain a significant improvement in device power conversion efficiency (PCE) to previously reported work using these materials. We obtain Si-PCPDTBT:fullerene and PCDTBT:fullerene-based inkjet-printed OPVs with power conversion efficiency of ~3% and ~4%, respectively. © 2014 Elsevier B.V. 130 474 480 Cited By :10

Five new polymers based on the 4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene core (BODIPY) chromophore moiety have been synthesized as low bandgap polymers for optoelectronic applications. The polymers exhibited high solubility in common organic solvents and optical bandgaps ranging from 1.7-2 eV. The materials were characterized using NMR, UV-Vis, steady state and time-resolved photoluminescence and the energy levels were examined using electrochemistry and validated using quantum chemical calculations. Finally, a representative BODIPY derivative : PCBM blend was examined in terms of photovoltaic properties. Preliminary device performance parameters as a function of photo-active layer thickness and composition are reported and discussed, relating to power conversion efficiency values. © The Royal Society of Chemistry 2013. 3 26 10221 10229

One of the factors limiting the performance of organic solar cells (OSCs) is their large energy losses (E loss) in the conversion from photons to electrons, typically believed to be around 0.6 eV and often higher than those of inorganic solar cells. In this work, a novel low band gap polymer PIDTT-TID with a optical gap of 1.49 eV is synthesized and used as the donor combined with PC71BM in solar cells. These solar cells attain a good power conversion efficiency of 6.7% with a high open-circuit voltage of 1.0 V, leading to the E loss as low as 0.49 eV. A systematic study indicates that the driving force in this donor and acceptor system is sufficient for charge generation with the low E loss. This work pushes the minimal E loss of OSCs down to 0.49 eV, approaching the values of some inorganic and hybrid solar cells. It indicates the potential for further enhancement of the performance of OSCs by improving their V oc since the E loss can be minimized. Refereed/Peer-reviewed

Here we report CdSe nanoplatelets that are incorporated into color-converting CdSe/ZnS nanocrystals for InGaN/GaN light-emitting diodes. The critical role of CdSe nanoplatelets as an exciton donor for the color conversion was experimentally investigated. The power conversion efficiency of the hybrid light-emitting diode was found to increase by 23% with the incorporation of the CdSe nanoplatelets. The performance enhancement is ascribed to efficient exciton transfer from the donor CdSe nanoplatelet quantum wells to the acceptor CdSe/ZnS nanocrystal quantum dots through F�rster-type nonradiative resonance energy transfer.

We present power conversion efficiency (PCE) and luminous efficiency (LE) performance levels of high photometric quality white LEDs integrated with quantum dots (QDs) achieving an averaged color rendering index of >= 90 (with R9 at least 70), a luminous efficacy of optical radiation of >= 380 lm/W-opt a correlated color temperature of

Using high surface area nanostructured electrodes in organic photovoltaic (OPV) devices is a route to enhanced power conversion efficiency. In this paper, indium tin oxide (ITO) and hybrid ITO/SiO2 nanopillars are employed as three-dimensional high surface area transparent electrodes in OPVs. The nanopillar arrays are fabricated via glancing angle deposition (GLAD) and electrochemically modified with nanofibrous PEDOT:PSS (poly(3,4- ethylenedioxythiophene):poly(p-styrenesulfonate)). The structures are found to have increased surface area as characterized by porosimetry. When applied as anodes in polymer/fullerene OPVs (architecture: commercial ITO/GLAD ITO/PEDOT:PSS/P3HT:PCBM/Al, where P3HT is 2,5-diyl-poly(3-hexylthiophene) and PCBM is [6,6]-phenyl-C61-butyric acid methyl ester), the air-processed solar cells incorporating high surface area, PEDOT:PSS-modified ITO nanoelectrode arrays operate with improved performance relative to devices processed identically on unstructured, commercial ITO substrates. The resulting power conversion efficiency is 2.2% which is a third greater than for devices prepared on commercial ITO. To further refine the structure, insulating SiO 2 caps are added above the GLAD ITO nanopillars to produce a hybrid ITO/SiO2 nanoelectrode. OPV devices based on this system show reduced electrical shorting and series resistance, and as a consequence, a further improved power conversion efficiency of 2.5% is recorded. © 2011 IOP Publishing Ltd.

We investigated the effect of solvents on the morphology, charge transport and device performance of poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5- (4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C71-butyric acid methyl ester (PC 70BM) based solar cells. To carry out this investigation, chloroform and 1,2-dichlorobenzene were chosen as good solvents of the two compounds. Films prepared with chloroform exhibit larger domains than those prepared with 1,2-dichlorobenzene and their size increases with the amount of PC 70BM. Fine tuning of the domain size was realized by using a solvent of mixed chloroform and 1,2-dichlorobenzene. At a mixing ratio of 50%:50%, a power conversion efficiency of 6.1% was achieved on PCDTBT:PC 70BM (1:3) devices with an active area of 1 cm 2, under air mass 1.5 global (AM 1.5 G) irradiation at 100 mW/cm 2. © 2011 Published by Elsevier B.V. All rights reserved.

Polymer-fullerene bulk heterojunction (BHJ) solar cells have gained much attention in the past few years due to their potential as a low cost photovoltaic technology. The state-of-the-art power conversion efficiency (PCE) has been improved to 7% regime by the recent development of thieno[3,4-b] thiophene based low-band-gap polymers. This paper reports a new low-band-gap polymer with alternating thieno[3,4-b]thiophene and benzo[1,2-b:4,5-b′] dithiophene units for applications in BHJ solar cells. By optimizing the nano-scale morphology with DIO (1,8-diiodooctane) additive, the PCE of BHJ solar cells based on this new polymer has been improved dramatically from 1.4% to 4.8%. The correlation between photovoltaic performance and film morphology has been established for this new polymer/fullerene system. © 2011 Elsevier B.V. All rights reserved.

A series of new dithieno[3,2-b:2′,3′-d]germole copolymers have been synthesized and characterized. The dithienogermole unit has been polymerized with different aromatic comonomers such as the benzothiadiazole (PGe1-C8 and PGe1-EH) and thieno[3,4-c]pyrrole-4,6-dione (PGe2). Suzuki and Stille coupling polymerizations under various conditions have been utilized. The polymers were then characterized by size-exclusion chromatography and thermal analyses (TGA, DSC), and their optical and electronic properties were investigated by UV-vis absorption spectroscopy and cyclic voltammetry. These low bandgap polymers (1.3-1.7 eV) have also been tested for photovoltaic applications; the best result was achieved with polymer PGe2, which shows a power conversion efficiency of 4.1%. © 2011 American Chemical Society.

A new alternating copolymer of dithienosilole and thienopyrrole-4,6-dione (PDTSTPD) possesses both a low optical bandgap (1.73 eV) and a deep highest occupied molecular orbital energy level (5.57 eV). The introduction of branched alkyl chains to the dithienosilole unit was found to be critical for the improvement of the polymer solubility. When blended with PC71BM, PDTSTPD exhibited a power conversion efficiency of 7.3% on the photovoltaic devices with an active area of 1 cm2. © 2011 American Chemical Society.

Incremental increase in dimethyl sulfoxide (or dimethyl formamide) in ortho-dichlorobenzene solution of poly [N -heptadecanyl-2,7-carbazole-alt-5,5- (4′, 7′ -di-2-thienyl- 2′, 1′, 3′ -benzothiadiazole)] (PCDTBT) gradually reduces the polymer-solvent interaction, the attraction forces between polymer chains become more dominant, and the polymer chains adopt a tight and contracted conformation with more interchain interactions, resulting in a progressive aggregation in both solutions and films. This was used to fine tune the morphology of PCDTBT/ PC71 BM based solar cells, leading to improved domain structure and hole mobility in the active layer, and significantly improved photovoltaic performance. The power conversion efficiency increased from 6.0% to 7.1% on devices with an active area of 1.0 cm2. © 2011 Crown.