Presence Of PCBM Research Articles

Engineering Surface Orientations for Efficient and Stable Hybrid Perovskite Single-Crystal Solar Cells

We synthesized two types of MAPbI3 single-crystal films with dominant (001) and (100) surface orientations for solar cells. We found that both MAPbI3 (001) and (100) single-crystal films have efficient hole transfer into poly(triaryl)amine (PTAA), as evident from the reduced photoluminescence (PL) intensity and lifetime, as well as the type-II energy alignment. Unlike a MAPbI3 (100) single-crystal film with a strong PL quenching due to efficient electron transfer to phenyl-C61-butyric acid methyl ester (PCBM), the MAPbI3 (001) single-crystal film exhibits an increase in PL intensity in the presence of PCBM, which can be attributed to surface passivation. Interestingly, different from the conventional MAPbI3 (100) that suffers from a significant decrease in the PCE (from 19.3 to 14.4%), the MAPbI3 (001) single-crystal film shows an increase in the PCE (from 16.0 to 17.2%) and much better stability under ambient conditions thanks to the dual passivation on the PbI2-rich surface by PCBM and O2.

Photoswitchable Solubility of Fullerene-Doped Polymer Thin Films

Controlling polymer film solubility is of fundamental and practical interest and is typically achieved by synthetically modifying the polymer structure to insert reactive groups. Here, we demonstrate that the addition of fullerenes or its derivatives (C60 or phenyl-C61-butyric acid methyl ester, PCBM) to polymers, followed by ultraviolet (UV) illumination can change the film solubility. Contrary to most synthetic polymers which dissolve in organic solvents but not in water, the fullerene-doped polymer films (such as polystyrene) can dissolve in water, yet remain stable in organic solvents. This photoswitchable solubility effect is not observed in either film constituents individually and derives from a synergy of photochemistries. Firstly, polymer photooxidation generates macroradicals which crosslink with radical-scavenging PCBM, thereby contributing to the films' insolubility in organic solvents. Secondly, light exposure enhances polymer photooxidation in the presence of PCBM via the singlet oxygen pathway. This results in polymer backbone scission and formation of photooxidised products which can form hydrogen bonds with water, both contributing to water solubility. Nevertheless, the illuminated doped polymer thin films are mechanically robust, exhibiting significantly increased modulus and density compared to their pristine counterpart, such that they can remain intact, even upon sonication in conventional organic solvents. We further demonstrate the application of this solubility-switching effect in dual tone photolithography, via a facile, economical and environmentally benign solution-processing route made possible by the photoactive nature of polymer-PCBM thin films.

High-Detectivity Perovskite Light Detectors Printed in Air from Benign Solvents

Summary Here, we propose a simple and low-temperature approach for the synthesis of methylammonium lead halide perovskite inks based on sub-micrometer-sized particles with tunable band gap. The particles allow the formulation of inks in benign solvents, such as propan-2-ol, and the printing of the photoactive layers of planar photoconductors with scalable, large-area coating techniques under ambient conditions. When surface traps are passivated with [6,6]-phenyl-C61-butyric acid methyl ester fullerene (PCBM), a high photoconductive gain (exceeding 200 in the blue) and reduced noise produce record-high specific detectivities exceeding 7 × 1013 cmHz0.5/W and gain-bandwidth product values of 7.5 × 106 Hz. Given the extreme simplicity of the presented device architecture and the straightforward processing, yielding printable light detectors rivalling established technologies, the present work promises a short-term deployment of printed perovskite detectors in a multitude of opto-electronic applications.

Assembly of poly-3-(hexylthiophene) nanocrystals in marginal solvent: The role of PCBM

Poly-3-(hexyl thiophene) (P3HT) represents the benchmark semiconducting polymer for the fabrication of organic photovoltaics (OPVs), where it acts as electron donor component in combination with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), as electron acceptor counterpart. The assembly of P3HT under marginal solvent conditions to form dispersions of fibrillar nanocrystals (NCs) is a particularly attractive method for the subsequent fabrication of highly crystalline films, if compared to depositions involving polymer solutions followed by relatively harsh thermal/solvent treatments, which are often incompatible with sensitive substrates. However, the mechanisms that drive the assembly of P3HT to NCs in marginal solvents are not fully understood, while the effects induced by the presence of PCBM during polymer assembly are still debated. In order to shed light into these processes, we systematically investigated the aggregation/crystallization behaviour of P3HT to NCs under different marginal-solvent conditions and in the presence of different relative contents of PCBM. The starting concentration of P3HT was shown to influence assembly kinetics, the micro-/nano-morphology and the photophysical properties of the formed NCs, as demonstrated by combining atomic force microscopy (AFM) and UV–vis adsorption spectroscopy. Polymer assembly to NCs was also highly dependent on the relative concentration of PCBM, within P3HT:PCBM mixtures typically applied in OPVs. In particular, the combination of UV–vis, AFM and wide-angle X-ray scattering (WAXD) highlighted that PCBM confined the aggregation/crystallization process of P3HT NCs, allowing the formation of extended crystallites, while at high concentrations it hindered the formation of NCs slowing down their assembly.

Impact of Alkyl Chain Length on Small Molecule Crystallization and Nanomorphology in Squaraine-Based Solution Processed Solar Cells

In this work, we have investigated a series of aniline-based squaraines, with varying solubilizing alkyl chains, as donor materials in bulk heterojunction (BHJ) solar cells. Although these squaraine molecules exhibit similar absorbance spectra and crystal structures, the difference in properties that drive the OPV performance becomes apparent when each squaraine is blended with PCBM. Thin film X-ray diffraction results demonstrate a disruption of squaraine crystallization in the presence of PCBM, more so for shorter side chain squaraines. As a result, the hole mobilities of BHJ films of shorter side chain squaraines show the largest drop when compared to their neat films, whereas the mobility decrease for the longer side chain counterparts is small. However, morphological studies have shown that the phase separation rapidly happens during the spin-casting process for longer side chain squaraines. Ultimately, it is the extent of phase separation that dominates the final device efficiency. Therefore, ration...

X-ray nanoscopy study on metal nano-structure formation at a metal-organic interface

Scanning transmission X-ray microscopy (STXM) with ~30-nm spatial resolution revealed at annealing effect on the metal-organic interface of an Al layer with a poly (3-hexylthiophene) (P3HT) organic semiconducting layer with and without phenyl-C61-butyric acid methyl ester (PCBM). In the case of a P3HT/Al layer with a high-tensile-strain organic over-layer, the overall interface changed to a zagged morphology with Al nano pillars after thermal annealing. On the contrary, a P3HT:PCBM/Al layer with a less-tensile-strain organic over-layer showed a smooth interface except for a few nano pillars. These interfacial morphology changes were related to the initial strain status and to the relaxation process and the phase separation of P3HT crystals relating to the PCBM. Grazing-incident wide-angle X-ray scattering (GI-WAXS) measurements were also conducted to examine the residual strain and the crystalline properties of P3HT in the presence of PCBM.

Polyazomethine as a component of solar cells-theoretical and optical study

A recently synthesized 25Th-cardo polyazomethine (PAZ) and its photocurrent generating junction with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have been examined as possible materials for construction of new-generation solar cells. Properties of a 25Th-cardo/PCBM system, where PAZ and PCBM act as donor and acceptor materials, respectively, have been studied theoretically by time-dependent density-functional theory (TD-DFT) and experimentally by means of optical absorption, photocurrent spectroscopy (PCS), and time-resolved luminescence (TRPL). Theoretical calculations show that highest occupied molecular orbital (HOMO) energy levels of PAZ and PCBM are almost equal (values of −6.01 and −5.98eV were obtained with the B3LYP functional and the def2-TZVP orbital basis for PAZ and PCBM, respectively), what suggests a possibility of charge transfer in both directions for this system. The shape of the calculated absorption spectrum is in a qualitative agreement with the experiment. The PCS measurements of the new material show that the external quantum efficiency is the highest (about 0.3%) in the near UV range. The TRPL studies reveal a fast decay of a Langevin type (in picosecond range) of the PAZ-related photoluminescence, which accelerates in presence of PCBM, probably due to the charge transfer to PCBM. In addition, our measurements document a usually neglected process of the hole transfer from a donor to an acceptor. A leakage of holes from PAZ to PCBM is supported by a small energy difference of the HOMO energies, as predicted by theory.

Fullerene-modified polyamide 6 by in situ anionic polymerization in the presence of PCBM

Activated anionic ring-opening polymerization of e-caprolactam (ECL) was carried out for the first time in the presence of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) to prepare polyamide 6 (PA6)-based composites comprising up to 3 wt% of this fullerene derivative. This in situ polymerization process produced high molecular weight composites containing 52–80 % of gel fraction at PCBM concentration ≥0.5 wt%. Spectral, thermo-mechanical, synchrotron X-ray, and scanning electron microscopy data were used to elucidate the structure and morphology of the PA6/PCBM composites. A mechanism of the chemical structure evolution was proposed starting with incipient complexation between ECL and PCBM, via subsequent chemical linking of ECL moieties on the C60 spheroid and final formation of star-burst and cross-linked morphologies. PCBM amounts of 0.1 wt% and more decreased the volume resistivity from 1012 Ω cm (neat PA6) to 109–107 Ω cm, thus opening the way for new applications of anionic PA6.

Spatial degradation mapping and component-wise degradation tracking in polymer–fullerene blends

P3HT degrades homogeneously and the degradation rate is reduced by a factor of 3 in the presence of PCBM. Spatial photodegradation maps are obtained by scanning transmission X-ray microscopy near the carbon absorption edge.

Electrogenerated Chemiluminescence and Fluorescence Lifetime Spatial Heterogeneity of Poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) in Presence of [6,6]-phenyl-C61-butyric Acid Methyl Ester

ABSTRACTWe present electrogenerated chemiluminescence (ECL) and fluorescence lifetime mapping of MEH-PPV/PCBM thin films. The ECL results show that the oxidation peak of MEH-PPV near 0.7 V (vs. SCE) and ECL response of films shifted positively towards 1.2 V in the presence of PCBM. At the same time, the oxidation current density of MEH-PPV increases along with the decrease of ECL intensity in the presence of PCBM. The fluorescence lifetime images clearly show that the lifetime spatial heterogeneities are affected by different substrates and MEH-PPV/PCBM ratios. Meanwhile, the lifetime of MEH-PPV decreases with the increasing of film thickness. The lifetimes of MEH-PPV films on TiO2 substrate are lower than films on glass.

Synthesis and photo-induced charge separation of confined conjugation length phenylene vinylene-based polymers

We report the synthesis and photophysics of four confined chromophore phenylene vinylene (PPV)-based polymers where PPV-type trimer chromophores are linked by alkyl ether chains of increasing length (PT3–PT6). These confined chromophore polymers were blended in a 1 : 1 w/w ratio with the fullerene derivative PCBM and the photoinduced charge-separation properties compared to that of a fully conjugated polymer analogue (alt-co-MEH-PPV). Fluorescence from all polymers is quenched in the presence of PCBM and transient absorption measurements confirm the presence of polymer polarons arising from charge transfer from the polymer to the PCBM acceptor. The polaron decay kinetics of all the blend films were similar but the yields of polarons for the confined conjugation length polymers were lower than for alt-co-MEH-PPV:PCBM. These observations suggest that many of the initially formed radical ion pairs for the confined length polymers are unable to fully charge dissociate and undergo fast geminate recombination.

Conjugated poly(azomethine)s via simple one-step polycondensation chemistry: synthesis, thermal and optoelectronic properties

Three conjugated triphenylamine-based poly(azomethine)s were prepared via well-known polycondensation chemistry using cheap and readily available starting materials and the results were contrasted with rrP3HT. Three functionalized diaminetriphenylamines (TPA(X), X ¼ –H, –OMe, –CN) were polymerized in a simple one-step process with 2,3-dihydrothieno[3,4-b][1,4]dioxine-5,7-dicarbaldehyde (ThOx), with water being the only side product. The resulting polymers (TPA(X)ThOx, X ¼ –H, –OMe, –CN) were characterized by GPC, IR and NMR, and show a good thermal stability. The opto-electronic properties could be tuned by changing the functionalization (X ¼ –H, –OMe, –CN) on the triphenylamine moiety. Photovoltaic devices based on TPA(X)ThOx/PCBM (1 : 2) showed power conversion efficiencies in the range of 0.02–0.04%. TRMC measurements showed that the presence of PCBM as an electron acceptor facilitates the formation of free mobile charges after excitation of the polymer. The low device efficiencies are attributed to a low hole-mobility of the polymer in combination with poor active layer morphology.

(Alkylsulfanyl)bithiophene‐alt‐Fluorene: π‐Conjugated Polymers for Organic Solar Cells

AbstractWe describe the synthesis of alternating bithiophene–fluorene copolymers (P1–P3) with different regiochemistry of the bithienyl unit and different alkylsulfanyl chain lengths. The structural, electrochemical and photophysical properties of these polymers were investigated by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), NMR, UV/Vis and photoluminescence (PL) spectroscopy and cyclic voltammetry (CV), and the polymers were used to assemble organic solar cells (OSCs), in combination with the fullerene derivative methyl [6,6]‐phenyl‐C61‐butyrate (PCBM). P3, with a head‐to‐head bithienyl unit, shows a broader absorption and a lower band gap with respect to P1 and P2, which have tail‐to‐tail bithienyl units. The PL intensity of P1–P3 is dramatically quenched in the presence of PCBM, demonstrating that an efficient charge transfer between donor and acceptor occurs. The best OSC device was obtained with P3.

Effects of Thermal Annealing Upon the Nanomorphology of Poly(3‐hexylselenophene)‐PCBM Blends

Grazing incidence X-ray diffraction (GI-XRD) is used to characterize the crystallographic dynamics of low molecular weight (LMW) and high molecular weight (HMW) poly(3-hexylselenophene) (P3HS) films and blend films of P3HS with [6-6-]-phenyl-C(61) -butyric acid methyl ester (PCBM) as a function of 'step-by-step' thermal annealing, from room temperature to 250 °C. The temperature-dependent GIXRD data show how the melting point of P3HS crystallites is decreased by the presence of PCBM. P3HS crystallite domain sizes dramatically increase upon annealing to the P3HS melting temperature. The formation of well-oriented HMW P3HS crystallites with the (100) plane parallel to the substrate (edge-on orientation), when cooled from melt, are observed. We compare the behaviour of P3HS pure and blend films with that of poly(3-hexyl)thiophene (P3HT) pure and PCBM blended films and suggest that the similar temperature dependent behaviour we observe may be a common to polythiophene and related polymers and their blends.

Synthesis and characterization of a thiophene-benzothiadiazole copolymer

The P3HT3BT copolymer was successfully synthesized via a multi-step procedure. The polymer absorbed light in a spectral range from UV region to near 600 nm. The energy band gap was estimated to be 1.98 eV and the polymer exhibited reversible oxidation-reduction cycles under the experimental conditions. In solid films, the PL emissions of the polymer were quenched in the presence of PCBM. Our current experimental data indicated that the polymer blends with PCBM can be employed in the fabrication of bulk heterojunction photovoltaic devices.

Single particle spectroscopy on composite MEH-PPV/PCBM nanoparticles

The preparation and characterization of composite MEH-PPV/PCBM nanoparticles with doping levels up to 75 wt% PCBM is reported. These nanoparticles represent structures in between single molecules and bulk that allow for a detailed investigation of the role of nanostructure on the properties of the corresponding functional materials. Combining this material system with single particle spectroscopy studies reveals molecular scale information on the extent to which variations in polymer chain folding and interactions between polymer chains and fullerenes affect material morphology and photophysical properties. Key observations are that the single particle ensemble spectra shift with respect to each other depending on PCBM doping levels, and that the vibronic structure of the single particle ensemble spectra changes with PCBM doping levels. These observations are indicative of a reduction in conducting polymer conjugation length and interchain interactions due to steric effects caused by the presence of PCBM that result in reduced exciton transport.

Photo- and thermal degradation of MDMO-PPV:PCBM blends

This paper is devoted to the study of the photo- and thermal-ageing of MDMO-poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene (PPV) blended with methano-fullerene[6,6]-phenyl C 61-butyric acid methyl ester ([60] PCBM), a commonly used active layer of organic solar cells. Thin films of MDMO-PPV, PCBM and MDMO-PPV:PCBM were submitted to photo- and thermal ageing in presence or in absence of oxygen. The modifications of the chemical structure of the materials were analysed by UV-visible and IR spectroscopies. Studying the degradation of pristine materials (MDMO-PPV and PCBM) permit the identification of the markers for characterizing the degradation of each component of the active layer. The degradation of MDMO-PPV was shown to involve a radicalar oxidation implying at first the ethers functions and secondly the double bonds; the photo-oxidation of PCBM was shown to involve the oxidation of its C 60 moiety. Photo-oxidation of MDMO-PPV:PCBM blends involved the degradation of both components and the presence of PCBM was observed to largely reduce the rate of degradation of MDMO-PPV in comparison with pristine MDMO-PPV. On a kinetic point of view, the same conclusion was obtained for thermo-oxidation and photolysis (irradiation in absence of oxygen). Our experimental results suggest that the decrease of the rate of degradation of MDMO-PPV in blended films during the three kind of ageing ( hυ, T, O 2) is mainly related to the radical scavenging properties of the PCBM.

Photoactive Blends of Poly(para-phenylenevinylene) (PPV) with Methanofullerenes from a Novel Precursor: Photophysics and Device Performance

Homogeneous blends of a processable methanofullerene, [6,6]-phenyl C61-butyric acid methyl ester (PCBM), with poly(para-phenylenevinylene) (PPV) synthesized using a novel nonionic precursor route were produced. These photoactive blends have been investigated by excited-state spectroscopy and by photocurrent measurements. UV−vis and IR absorption measurements, as well as luminescence spectroscopy, were used to monitor the conversion process of the precursor polymer to the PPV in blends with PCBM. The presence of PCBM did not influence the successful conversion process. The occurrence of photoinduced charge transfer, well-known for blends of substituted PPV with fullerenes, was evidenced in composites of PPV/PCBM by the strong quenching of the PPV luminescence. LESR (light induced electron spin resonance) and PIA (photoinduced absorption) studies confirmed the occurrence of photoinduced electron transfer from the PPV to PCBM within the bulk of solid state composite films. Photovoltaic devices made from PPV/...