Phenyl C61-butyric Acid Methylester Blend Research Articles

Dipolar self-assembled monolayers grafted on ZnO for the tuning of electronic properties of the poly (3-hexylthiophène)- [6,6]-phenyl C61-butyric acid methylester blend

A promising solution to improve the performance of Bulk heterojunction organic photovoltaic devices is the insertion of functionalized self-assembled monolayers (SAMs) at the interface between the Electron Transporting Layer (ETL) and the active layer. By grafting such dipolar SAMs based on Y-PP-COOH (P = Phenyl, YY= CH3O, F)) on a ZnO ETL, both the electronic and the chemical properties of the interface are modified. The growth of the active blend the poly(3-hexylthiophène)- [6,6]-phenyl C61-butyric acid methylester blend deposited onto the SAMs is also altered. The dipole with a component oriented perpendicularly to the ZnO surface modifies the ZnO work function whereas the surface energy of the SAM influences the microstructuration of the active material. When we analyze the inverted photovoltaic cell, we find that the two effects may be distinguished: the CH3O moiety favorably affects the electrical transfer of carriers with mainly an improvement of the open-circuit voltage Voc whereas fluorine disfavors both electron extraction and blend microstructure quality, with a lower Voc and electrical current density Jsc.

Effect of fullerene doping on the electrical properties of P3HT/PCBM layers

Poly (3-hexylthiophene-2, 5-diyl) (P3HT) and its blend with Phenyl-C61-Butyric acid-Methyl-Ester (PCBM) and fullerene (C60) thin films were prepared and their electrical properties for memory applications were studied. Due to doping, a sharp decrease in the resistance for a P3HT:PCBM:C60 device was observed at around 70°C which makes it useful for thermal switching applications. Addition of C60 to P3HT:PCBM blend gave a high value for RRESET/RSET in thermal switching. For bias switching, threshold voltage reduces to 1.4V from 25V with the addition of C60 to P3HT layer.

P3HT:PCBM blend based photo organic field effect transistor

In this work, we have fabricated photo organic field effect transistor using the blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methylester (PCBM) as active layer. Transistor was fabricated in MESFET type configuration with top gate and bottom drain source contacts on glass substrate. Drain and source contacts were made using Silver (Ag) whereas gate contact was made by depositing Aluminum (Al) on the active layer. Active layer showed Ohmic type contact with drain/source electrodes and Schottky type contact with gate electrode which was discussed with help of energy band diagram. I–V characteristics of the device were investigated under dark and UV–Vis illumination, and these were found similar to p-type mode I–V characteristics of a typical ambipolar field effect transistor. Further, device has shown low voltage operation with weak saturation trend under illumination. Field effect mobility and photo responsivity values of the device were found higher as compared to reported organic photo-MESFETs. Realization of such low voltage devices will provide potential for the development of low cost large area flexible sensor arrays and other low power electronic devices in future.

Dipyrrolidinyl-substituted perylene diimide as additive for poly(3-hexylthiophene): [6,6]-Phenyl C61 butyric acid methylester bulk-heterojunction blends

The effects of the addition of 1,7-dipyrrolidinyl-substituted perylene diimide (1,7-PyPDI) to a traditional poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methylester (PCBM) bulk-heterojunction blend on the performance of organic solar cells, are described. When the 1,7-PyPDI amount in the mixture is accurately tuned, the power conversion efficiency (η) of the 1,7-PyPDI-doped cells is enhanced compared to a reference non-doped device. Cells fabricated by spin-coating blends from chloroform solution with P3HT (monomer):PCBM:1,7-PyPDI molar ratio of 6.85:1:0.03 resulted in 39.6% higher power conversion efficiency than P3HT:PCBM blend. The efficiency improvement is attributed to possible photochemical interactions between the three components of the blend, which contribute to enhance the charge separation, and minimize the charge recombination processes. Moreover, the increased absorption and the microstructural implications induced by the introduction of 1,7-PyPDI contribute to explain the enhancement of the solar cell performance.

Influence of Thickness and Annealing Temperature on the Optical Properties of Spin-Coated Photoactive P3HT:PCBM Blend

Influence of annealing temperature and thickness on the optical characteristics of the blend of poly (3-hexylthiophene) (P3HT) and Phenyl C61 butyric acid methylester (PCBM) layer has been investigated in this report. Photoactive polymer material (P3HT:PCBM) was deposited on indium tin oxide (ITO) substrate by spin-coating. The morphology of P3HT:PCBM composite layer was investigated by Atomic Force Microscope (AFM). The surface roughness was found to reduce after heat treatment. The absorption of the composite layer was found to increase with its number of layer (thickness). On the other hand, the photoluminescence (PL) quenching, which indicates efficient charge separation in the bulk heterojunction, was found higher for the thinner layer. Absorption was also found to increase with the annealing temperature. Therefore, to optimize the thickness of the P3HT:PCBM photoactive layer that will provide best absorption while providing efficient charge separation, annealing at optimized temperature might be an effective tool.

Current Conduction in Poly(3-Hexylthiophene) and in Poly(3- Hexylthiophene) doped [6,6]-Phenyl C61-Butyric Acid Methylester Composite Thin Film Devices

Transport properties of poly(3-hexylthiophene) (P3HT), and of its blend with [6,6]-phenyl C61- butyric acid methylester (PCBM), were studied by analysing temperature dependent current-voltage characteristics of spin cast thin films sandwiched between aluminium electrodes in a metal-insulator- metal (MIM) configuration. It was found that in Al/P3HT/Al devices, the current is limited by space charge that accumulates near the hole injecting electrode due to the poor bulk transport properties of P3HT. At low temperatures and high applied electric fields the current density obeys a power law of the form J _ Vm, characteristic of space charge limited current (SCLC) in the presence of exponentially distributed traps within the band gap. These traps are filled by charge that is injected by quantum mechanical tunnelling, which is adequately described by the Fowler-Nordheim (FN) theory. By calculating the majority charge carrier mobility in Al/P3HT/Al and Al/P3HT:PCBM/Al devices from the Ohmic, SCLC, and FN tunnelling fits at different temperatures, we have obtained that the charge carrier mobility in P3HT is two orders smaller than the electron mobility in the P3HT:PCBM blend at room temperature, but comparable at low temperatures. This information is important in determining the origin of open circuit voltage and short circuit current limit in solar cells that employ this blend as the active layer.

Binding energy of singlet excitons and charge transfer complexes in MDMO‐PPV:PCBM solar cells

AbstractThe influence of an external electric field on the photoluminescence intensity of singlet excitons and charge transfer complexes is investigated for a poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene] (MDMO‐PPV) diode and a bulk heterojunction of the PPV in combination with [6,6]‐phenyl‐C61 butyric acid methylester (PCBM), respectively. The experimental data is related to the dissociation probability derived from the Onsager–Braun model. In this way, a lower limit for the singlet exciton binding energy of MDMO‐PPV is determined as $ (327 \pm 30) $ meV, whereas a significantly lower value of $ (203 \pm 18) $ meV is extracted for the charge transfer complex in a MDMO‐PPV:PCBM blend. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Room to Improve Conjugated Polymer-Based Solar Cells: Understanding How Thermal Annealing Affects the Fullerene Component of a Bulk Heterojunction Photovoltaic Device

We examine how thermal annealing affects the fullerene network in conjugated polymer bulk heterojunction (BHJ) solar cells. We begin by creating electron-only devices with a BHJ geometry by blending the fullerene derivative [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) with polystyrene (PS). These electron-only PS:PCBM diodes function even with a poly(ethylenedioxithiophene):poly(styrenesulfonate) (PEDOT:PSS) layer, indicating that PEDOT:PSS films do not serve as electron blocking layers. Atomic force microscopy shows that the degree of phase segregation in the PS:PCBM blend films is similar to that in the active layer of blends of PCBM with poly(3-hexylthiophene-2,5-diyl) (P3HT), so that the PS:PCBM blends provide a good model for the fullerene part of the BHJ network in P3HT:PCBM solar cells. We find that thermal annealing dramatically decreases the electron current that flows in the PS:PCBM diodes, suggesting that annealing leads to increased phase segregation that lowers the electron mobility on fullerenes in the BHJ geometry. We also find that annealing increases the photoluminesence of P3HT:PCBM blend films, indicating that thermal treatment produces increased phase segregation that leads to decreased exciton harvesting. The fact that annealing decreases both exciton harvesting and electron mobility implies that there is significant room to further improve polymer/fullerene photovoltaics by controlling the amount of phase segregation.

Ultrafast spectroscopic studies in polyfluorene: [6,6]-phenylC61-butyric acid methyl ester blend films: monitoring the photoinduced charge transferprocess

We present a study of charge transfer in polyfluorene: [6,6]-phenylC61-butyric acid methyl ester (PCBM) blend films. After photoexciting the conjugatedpolymer, electrons are very quickly transferred onto the PCBM leaving positive charges inthe polymer. The presence of new photogenerated species in both polymer andPCBM can be demonstrated by photoinduced optical absorption studies. Usingultrafast spectroscopic experiments, not only are we able to demonstrate the chargetransfer process in such composites but also we can time resolve the dynamics ofthe process. Charge transfer is, in this way, estimated to take place ps after photoexcitation. After ps all charges have already been transferred and the process concludes. The resultingseparated charges have the potential to produce a photocurrent if they are successfullydriven through the bulk and collected by suitable electrodes.