wangzhaowei

Roles of fullerene-based interlayers in enhancing the performance of organometal perovskite thin-film solar cells are elucidated. By studying various fullerenes, a clear correlation between the electron mobility of fullerenes and the resulting performance of derived devices is determined. The metallic characteristics of the bilayer perovskite/fullerene field-effect transistor indicates an effective charge redistribution occurring at the corresponding interface. A conventional perovskite thin-film solar cell derived from the C₆₀ electron-transporting layer (ETL) affords a high power conversion efficiency of 15.4%.

A hybrid ultratransparent poly(3,4-ethyl­enedioxythiophene):poly(styrenesulf­onate) (PEDOT:PSS)/metal grid thin-film is demonstrated as a transparent electrode for organic solar cells. The transmittance of the PEDOT:PSS thin-films on glass reaches values as high as 91.5%, a nearly 100% transmittance ratio. The device with the hybrid electrode shows an efficiency of 2.8%, which is comparable to that of an indium tin oxide based reference device.

A bis-azide-based small molecule cross­linker is synthesized and evaluated as both a stabilizing and efficiency-boosting additive in bulk heterojunction organic photovoltaic cells. Activated by a non­invasive and scalable solution processing technique, polymer:fullerene blends exhibit improved thermal stability with suppressed polymer skin formation at the cathode and frustrated fullerene aggregation on ageing, with initial efficiency increased from 6% to 7%.

The impact of additives mixed with poly(3,4-ethylenedioxythiophene):polysty­renesulfonate (PEDOT:PSS) on the stability of organic photovoltaic modules is investigated for fully ambient roll-to-roll (R2R) processed indium tin oxide free modules. Four different PEDOT:PSS inks from two different suppliers are used. The modules are manufactured directly on barrier foil without a UV filter to accelerate degradation and enable completion of the study in a reasonable time span. The modules are subjected to stability testing following well-established protocols developed by the international summit on organic photovoltaic stability (ISOS). For the harsh indoor test (ISOS-L-3) only a slight difference in stability is observed between the different modules. During both ISOS-L-3 and ISOS-D-3 one new failure mode is observed as a result of tiny air inclusions in the barrier foil and a R2R method is developed to detect and quantify these. During outdoor operation (ISOS-O-1) the use of ethylene glycol (EG) as an additive is found to drastically increase the operational stability of the modules as compared to dimethylsulfoxide (DMSO) and a new failure mode specific to modules with DMSO as the additive is identified. The data are extended in an ongoing experiment where DMSO is used as additive for long-term outdoor testing in a solar park.

Long term stability testing following the international summit on organic photovoltaic stability protocols is used for evaluation of poly(3,4-ethylenedioxythio­phene):polystyrenesulfonate (PEDOT:PSS) based roll-to-roll processed polymer solar cell modules. The influence of the choice of additives on the operational lifetime for the devices is analyzed according to the observed failure modes and predictions of the operational window are made.

The results presented demonstrate how the screening of 104 light-absorbing low band gap polymers for suitability in roll coated polymer solar cells can be accomplished through rational synthesis according to a matrix where 8 donor and 13 acceptor units are organized in rows and columns. Synthesis of all the polymers corresponding to all combinations of donor and acceptor units is followed by characterization of all the materials with respect to molecular weight, electrochemical energy levels, band gaps, photochemical stability, carrier mobility, and photovoltaic parameters. The photovoltaic evaluation is carried out with specific reference to scalable manufacture, which includes large area (1 cm²), stable inverted device architecture, an indium-tin-oxide-free fully printed flexible front electrode with ZnO/PEDOT:PSS (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate), and a printed silver comb back electrode structure. The matrix organization enables fast identification of active layer materials according to a weighted merit factor that includes more than simply the power conversion efficiency and is used as a method to identify the lead candidates. Based on several characteristics included in the merit factor, it is found that 13 out of the 104 synthesized polymers outperformed poly(3-hexylthiophene) under the chosen processing conditions and thus can be suitable for further development.

A screening of 104 polymer materials for use in roll-coated polymer solar cells is reported. By synthesis, characterization, and photovoltaic performances of 104 polymers it is demonstrated that finding suitable materials for large scale roll-to-roll fabricated polymer solar cells is an enormous challenge. The study shows that 13 polymers out of 104 outperform poly(3-hexylthiophene) (P3HT) and are suitable for further development.

Poly(benzo[1,2-b:4,5-b′]dithiophene–alt–thieno[3,4-c]pyrrole-4,6-dione) (PBDTTPD) polymer donors with linear side-chains yield bulk-heterojunction (BHJ) solar cell power conversion efficiencies (PCEs) of about 4% with phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as the acceptor, while a PBDTTPD polymer with a combination of branched and linear substituents yields a doubling of the PCE to 8%. Using transient optical spectroscopy it is shown that while the exciton dissociation and ultrafast charge generation steps are not strongly affected by the side chain modifications, the polymer with branched side chains exhibits a decreased rate of nongeminate recombination and a lower fraction of sub-nanosecond geminate recombination. In turn the yield of long-lived charge carriers increases, resulting in a 33% increase in short circuit current (J _sc). In parallel, the two polymers show distinct grazing incidence X-ray scattering spectra indicative of the presence of stacks with different orientation patterns in optimized thin-film BHJ devices. Independent of the packing pattern the spectroscopic data also reveals the existence of polymer aggregates in the pristine polymer films as well as in both blends which trap excitons and hinder their dissociation.

The polymer side chain pattern determines the efficiency of PBDTTPD:phenyl-C61/71-butyric acid methyl ester solar cells because it changes the yield of free charges and the nongeminate recombination dynamics, as demonstrated using broadband transient pump–probe spectroscopy. Tuning of the side chains leads to a doubling of the power conversion efficiency from 4% up to 8%.

The study of the perovskite solar cells provides insight into the optimum morphology. A bilayer structure is required for efficient solar cells, and one with a high efficiencies of up to 15.2% and an open-circuit voltage (V_oc) up to 1110 mV is demonstrated. Furthermore, the 80% high yield also paves the way for the possibility of mass production in the future.

In article number 1401130, Dong Ick Son and co-workers demonstrate inverted polymer solar cells (iPSCs) containing a quantum dot (QD) monolayer that bonds with the low-work function (WF) organic material polyethylenimine ethoxylated (PEIE) by electrostatic interaction. The PEIE/monolayered QD heterostructures serve as the electron transport layer, absorption layer, and surface plasmon resonance (SPR) trigger for improving photovoltaic performance. The iPSCs enhance the power conversion efficiency (PCE) more than 20%, with an 8.1% maximum PCE.

Organic vapor phase deposition is used to grow a roughened active layer for an organic photovoltaic cell that suppresses morphological changes in a subsequently deposited Bphen blocking layer. Bphen grown on smooth active layers grown by vacuum thermal evaporation crystallizes due to lack of morphological “pinning.” Morphological pinning leads to improved operational device lifetime of the organic vapor phase deposition-grown organic photovoltaic cells.

The successful application of an effective dipolar interface layer based on an amine functionalized fullerene derivative (DMAPA-C₆₀) is reported for the perovskite and organic photovoltaic devices. The incorporation of DMAPA-C₆₀ facilitates a favorable energy level alignment, and results in enhanced mobility-lifetime (µt) product.

The combined optical management of an optical cavity and a photonic crystal, reported by Jordi Martorell and co-workers in article number 1400614, enhances the performance of semitransparent organic solar cells to achieve power conversion efficiencies comparable to the ones seen in the corresponding opaque cells. This result makes it possible to create window-integrated photovoltaic solutions without compromising power conversion.

Novel large π-conjugated carbon material, graphdiyne (GD), as a dopant to poly(3-hexylthiophene) (P3HT) hole-transporting material (HTM) layer, is introduced into perovskite solar cells for the first time. Raman spectroscopy and ultraviolet photoelectron spectroscopy measurements reveal that relatively strong π–π stacking interaction occurs between GD particles and P3HT (so-called P3HT/GD composite HTM), favorable for the hole transportation and improvement of the cell performance. On the other hand, some GD aggregates exhibit a scattering nature, and thus help to increase the light absorption of the perovskite solar cells in the long wavelength range. As high as 14.58% light-to-electricity conversion efficiency is achieved, superior to the pristine P3HT-based devices. Additionally, the devices exhibit good stability and reproducibility. Time-resolved photoluminescence decay measurements reveal that the P3HT/GD HTM can accelerate the hole extraction compared with pristine P3HT.

A novel large π-conjugated carbon material , graphdiyne (GD), is introduced into perovskite solar cells for the first time. As a dopant to poly(3-hexylthiophene) (P3HT) hole-transporting material, GD exhibits relatively strong π–π stacking interaction with P3HT, yielding a high power conversion efficiency value of 14.58% with good stability and reproducibility, superior to the pristine P3HT-based devices.

The phenoxazine-based acceptor–donor–acceptor structured small-molecule material M1 is used either as a hole-transport material in (CH₃NH₃)PbI₃-perovskite-based solar cells or as photoactive donor material in bulk heterojunction organic solar cells. Excellent power conversion efficiencies of 13.2% and 6.9% are achieved in these two types of photovoltaic devices, respectively.

Flexible perovskite photovoltaic modules are demonstrated for the first time. Low-temperature processes including UV-irradiation of the mesoporous TiO₂ and atomic layer deposition of the compact TiO₂ helps deliver solar cells with 8.4% efficiency, good flexibility, and improved stability with respect to scaffoldless equivalents. Screen-printable scaffolds and masking/laser patterning procedures enables fabrication of 3.1%-efficient mesostructured perovskite modules on plastic substrates.

In article number 1400919, John A. Rogers and co-workers report a thin-film multijunction solar cell architecture employing low refractive index air gaps as interfaces. Experimental devices using such a scheme exhibit enhanced photon recycling processes, suggesting a new path to realize photo-voltaic devices that utilize the entire solar spectrum and approach the thermodynamic efficiency limits.

Unlike universally applicable fullerene derivatives, current nonfullerene electron acceptors are rarely effective with more than one donor polymer in bulk heterojunction (BHJ) solar cells. A novel class of nonfullerene electron acceptors, bis(naphthalene imide)-3,6-diphenyl-trans-anthrazolines (BNIDPAs), that is applicable and yields efficient photovoltaic devices with multiple donor polymers, including a thiazolothiazole–dithienosilole copolymer (PSEHTT) and benzodithiophene copolymers (PBDTT-FTTE and PTB7) is reported. Photovoltaic devices composed of the BNIDPA-butyloctyl (BO) acceptor with PSEHTT, PBDTT-FTTE, and PTB7, respectively, have power conversion efficiencies of 3.0%–3.1% with high open-circuit voltages of ≈1.0 V. In contrast, BHJ devices composed of BNIDPA-DT acceptor with larger 2-decyltetradecyl chains and the same donor polymers have substantially reduced bulk electron mobility and reduced photovoltaic efficiencies of 1.3%–1.7%, which highlight the critical role of the size of alkyl chains appended onto nonfullerene electron acceptors. The present results provide a rare example of nonfullerene electron acceptors that are capable of pairing with multiple donor polymers to achieve efficient BHJ solar cells.

Novel nonfullerene electron acceptors, bis[naphthalene imide)diphenylanthrazolines, are found to be compatible with multiple donor polymers, enabling polymer solar cells with power conversion efficiencies of 3.0%–3.1% and high photovoltages of close to 1.0 V. The size of the alkyl chain appended onto a nonfullerene acceptor is found to dramatically change the photovoltaic efficiency.

Solution-processed organic bulk heterojunction solar cells based on poly(3-hexylthiophene) (P3HT) blended with [6,6]-phenyl-C₆₀-butyric acid methyl ester are doped with different concentrations of iron (II,III) oxide nanoparticles (Fe₃O₄). The power conversion efficiency of the devices doped at low concentrations is improved up to 11%. The improvement finds its origin in a lower recombination current, which is a consequence of an increased effective exciton lifetime according to the J–V characteristics and the optoelectronical analysis of the films. The increase in performance cannot be attributed to changes in morphology or crystallinity according to grazing-incidence X-ray scattering experiments. The evolution of the solar cell short-circuit current at low doping concentrations is related to variations in the arrangement of the crystalline regions of P3HT. For high doping concentrations (above 1.0 wt%) the performance of the solar cell decays rapidly, ascribed to the increased leakage currents in the device caused by the presence of nanoparticles.

Organic solar cells are doped with iron oxide nanoparticles. An increased efficiency for low doping concentrations is found and ascribed to a reduced device recombination, which is traced with prompt and delayed fluorescence measurements. Morphological and crystalline characterization is addressed by grazing-incidence small/wide-angle X-ray scattering in order to ensure that the improvement is not morphology related.