Blend Of P3HT Research Articles

Gas expanded polymer process to anneal nanoparticle dispersion in thin films

Organic photovoltaic (OPV) active layers made by spin-coating a solution comprising poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) nanoparticles have been shown to adopt a non-uniform concentration profile across the thin film dimension. This inhomogeneous distribution can reduce the efficiency of the device. In the present work a new process, gas expanded polymer (GXP) annealing, is applied to P3HT/PCBM thin film blends, enabling the distribution of the PCBM nanoparticles to be manipulated by varying the GXP processing conditions. Films of 50nm thickness (nominally) created by spin casting a blend of P3HT mixed with PCBM were annealed by oscillatory GXP and GXP at constant pressure using high pressure CO2. An increase in P3HT crystallinity (detected by X-ray diffraction and UV–vis spectroscopy) along with a more uniform distribution of PCBM nanoparticles in the thickness dimension, as interpreted from neutron reflectivity measurements, were observed after oscillatory GXP annealing. In addition, static water contact angles suggest that the film/air interface is enriched in PCBM relative to the as-cast film. These results demonstrate that GXP annealing, which is commercially scalable, can be successfully used to create a uniform distribution of PCBM nanoparticles across the thickness dimension in a P3HT thin film.

Photoinduced Dynamics of Charge Separation: From Photosynthesis to Polymer-Fullerene Bulk Heterojunctions.

Understanding charge separation and charge transport is crucial for improving the efficiency of organic solar cells. Their active media are based on organic molecules and polymers, serving as both light-absorbing and transport layers. The charge-transfer (CT) states play an important role, being intermediate for free carrier generation and charge recombination. Here, we use light-induced electron paramagnetic resonance spectroscopy to study the CT dynamics in blends of the polymers P3HT, PCDTBT, and PTB7 with the fullerene derivative C60-PCBM. Time-resolved EPR measurements show strong spin-polarization patterns for all polymer-fullerene blends, confirming predominant generation of singlet CT states and partial orientation ordering near the donor-acceptor interface. These observations allow a comparison with charge separation processes in molecular donor-acceptor systems and in natural and artificial photosynthetic assemblies, and thus the elucidation of the initial steps of sequential CT in organic photovoltaic materials.

Enhanced charge separation in ternary P3HT/PCBM/CuInS2 nanocrystals hybrid solar cells.

Geminate recombination of bound polaron pairs at the donor/acceptor interface is one of the major loss mechanisms in organic bulk heterojunction solar cells. One way to overcome Coulomb attraction between opposite charge carriers and to achieve their full dissociation is the introduction of high dielectric permittivity materials such as nanoparticles of narrow band gap semiconductors. We selected CuInS2 nanocrystals of 7.4 nm size, which present intermediate energy levels with respect to poly(3-hexylthiophene) (P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM). Efficient charge transfer from P3HT to nanocrystals takes place as evidenced by light-induced electron spin resonance. Charge transfer between nanocrystals and PCBM only occurs after replacing bulky dodecanethiol (DDT) surface ligands with shorter 1,2-ethylhexanethiol (EHT) ligands. Solar cells containing in the active layer a ternary blend of P3HT:PCBM:CuInS2-EHT nanocrystals in 1:1:0.5 mass ratio show strongly improved short circuit current density and a higher fill factor with respect to the P3HT:PCBM reference device. Complementary measurements of the absorption properties, external quantum efficiency and charge carrier mobility indicate that enhanced charge separation in the ternary blend is at the origin of the observed behavior. The same trend is observed for blends using the glassy polymer poly(triarylamine) (PTAA).

溶剂挥发时间对体异质结有机太阳能电池复合特性的影响

The bulk heterojunction organic solar cells based on compositional blend of P3 HT and PCBM were fabricated,the relationships among the carrier recombination loss,device manufacturing conditions and interface trap density were studied by changing the spin velocity and spin coating time to control the solvent evaporation time in the mixed film. The results show that the evaporation time of active composite film directly influences the photoelectric performance of organic solar cell. The device that the solvent evaporates faster can produce stronger trap-assisted recombination,it's interface trap density is larger,and the slope of the open circuit voltage versus the logarithm of the light intensity is greater. A numerical relationship among the manufacturing processing conditions,recombination loss mechanism,interface trap density and the device optoelectronic characteristics has been established in this paper,which can offer good guidance to improve the performance of polymer solar cells.

Photoelectrical Properties of Fullerene Doped P3HT Blends for Photo Sensing Applications

Photoelectrical properties of fullerene (C60) doped spin coated thin films of Poly (3-hexylthiophene 2,5 diyl) (P3HT) and its blend with Phenyl-C61Butyric-Acid-Methyl-Ester (PCBM) were studied. Photoresponse characteristics were studied by noting the resistance variation with exposure to illumination, as a function of time. Decrease of resistance to the exposure of light was observed in both P3HT and its blend films indicating their high sensitivity to light. On/off ratio of resistance was 150 for P3HT devices and relative current change (photoresponse), ΔIrep= Ilight/Idark was a high value of 166 in P3HT devices. P3HT devices showed a periodic and stable response characteristics compared to the P3HT blend devices for several sensing cycles of photoelectrical studies.

Spiro-1,3-dioxolanofullerenes with Low-lying LUMO Level for Organic Solar Cells

Abstract A series of spiro-1,3-dioxolanofullerenes with 6-, 7-, 8-, and 12-membered ring were synthesized by the acid-catalyzed reaction of fullerene epoxide with cycloalkanones. The LUMO levels of these fullerenes are 0.07–0.08 eV lower than that of PCBM, due to the electron-withdrawing ester directly bonded to the C60 core. However, good power conversion efficiencies of 2.9 and 5.4% were obtained for the P3HT and PTB7 blend films, respectively. Characterization by solubility and morphology aided the understanding of the limiting factors behind the photovoltaic performance.

Development of bulk heterojunction morphology by the difference of intermolecular interaction behaviors

The morphology of a bulk heterojunction can be controlled by adding a processing additive in order to improve its power conversion efficiency (PCE) in photovoltaic devices. The phase-separated morphologies of blends of PONTBT or P3HT with fullerene derivatives are systematically examined in the presence of processing additives that possess various alkane alkyl chain lengths or end-group electronegativities. We determined the morphologies of the bulk heterojunction layers by using atomic force microscopy (AFM) and grazing incidence wide angle X-ray scattering (GIWAXS). The photocurrent–voltage characteristics of the bulk heterojunction solar cells were found to be strongly dependent on the intermolecular interactions between the conjugated polymers, the fullerene derivatives, and the processing additives in the photoactive layer. The optimal PONTBT:fullerene derivative blend morphology was obtained with a processing additive, 1,3-diiodopropane (1,3-DIP), that possesses a short alkyl chain and an end group with weak electronegativity, and was found to exhibit a high fill factor (FF) and a high current density (JSC). In contrast, in blends of P3HT with the fullerene derivative, PCEs with higher FF and JSC values were achieved by incorporating the processing additive, 1,8-dibromooctane (1,8-DBrO), which has a long alkyl chain and a strong electronegative end group. Thus the selection of the processing additive with the aim of enhancing photovoltaic performance needs to take into account the intermolecular interaction of the conjugated polymer.

Elaboration of Conductive Polymer thin films (P3HT/PCBM) by spin coating method – Application for hybrid organic solar cell

The nanostructured polymer-fullerene thin film is one of the most prominent materials to make the hybrid bulk heterojunction solar cell (BHJ) with high conversion efficiency. Especially when the blend of P3HT and PCBM was used as the donor and acceptor materials. The properties of P3HT and PCBM layer in solar cell has been much studied and considered as high performance systems. One of the important factors for the high performance device is the fabrication of photo active layer with the appropriate thickness and morphology. In the ideal case, the intermolecular distance between the polymer and fullerene should be approximately 10-20 nm (the exciton diffusion distance) giving an area of extensive contact between the two phases. After the dissociation of carriers, the two polymer phases should create the path way for carriers to reach electrodes. But so far, this ideal configuration has not been published. In this work, we’ve elaborated the P3HT and PCBM photo active layers by spin coating methodon glass substrates covered ITO electrode. The rotational velocity was determined to get the necessary effective thickness of the polymer film. The annealing effect on structure, optical and electrical properties of the polymer thin film with different content of PCBM were also investigated. The experiments show the best device on electrode ITO has I-V characteristic as a photodiode and short circuit current (Isc) aboutmili-Ampere. These results demonstrate convincingly that polymer layers elaborated by spin coating method can result a good performance of the device.

Multiscale active layer morphologies for organic photovoltaics through self-assembly of nanospheres.

We address here the need for a general strategy to control molecular assembly over multiple length scales. Efficient organic photovoltaics require an active layer comprised of a mesoscale interconnected networks of nanoscale aggregates of semiconductors. We demonstrate a method, using principles of molecular self-assembly and geometric packing, for controlled assembly of semiconductors at the nanoscale and mesoscale. Nanoparticles of poly(3-hexylthiophene) (P3HT) or [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were fabricated with targeted sizes. Nanoparticles containing a blend of both P3HT and PCBM were also fabricated. The active layer morphology was tuned by the changing particle composition, particle radii, and the ratios of P3HT:PCBM particles. Photovoltaic devices were fabricated from these aqueous nanoparticle dispersions with comparable device performance to typical bulk-heterojunction devices. Our strategy opens a revolutionary pathway to study and tune the active layer morphology systematically while exercising control of the component assembly at multiple length scales.

Ternary hybrid systems of P3HT-CdSe-WS₂ nanotubes for photovoltaic applications.

Hybrid heterojunctions of conjugated polymers and inorganic nanomaterials are a promising combination for obtaining high performance solar cells (SC). In this work we have explored new possible uses of the WS2 nanotubes (NTs) both as the only acceptor material blended with a polymer and in ternary systems mixed with a polymer and quantum dots (QDs). In particular we have spectroscopically investigated binary blends of poly(3-hexylthiophene) (P3HT) and WS2 NTs, P3HT and CdSe QDs, and ternary blends of P3HT, CdSe QDs and WS2 NTs. We report fluorescence quenching effects of the QD signal in the P3HT-CdSe-WS2 system with the increase of NT concentration. Static and time-resolved fluorescence studies reveal efficient resonant energy transfer from the QDs to the NTs upon photoexcitation. The evidence of energetic interaction between WS2 NTs and QDs opens new fields of application of WS2 NTs and holds very promising potential for improving charge transfer phenomena in the active layer of hybrid solar cells.

In situ photoluminescence probe to study the melting behavior of regioregular poly(3-hexylthiophene)

In situ photoluminescence (PL) measurements for regioregular poly(3-hexylthiophene) (rr-P3HT) at various annealing temperatures were performed. When the annealing temperature is above , the PL spectra exhibit two significant changes: a sudden increase of integrated intensity and the appearance of a grand new peak at higher energy. According to the corresponding absorbance spectra, it was found that these changes in PL spectra are originated from the torsional defects in the P3HT backbone introduced by melting transition. Furthermore, the variation trend of the new peak to whole PL emission intensity ratio almost overlaps with the endothermic peak in the Differential Scanning Calorimeter (DSC) thermogram. It gives direct evidence that the intensity ratio can be used as a semi-quantitative probe to the melting degree of P3HT. Then, the P3HT melting behavior in a blend of P3HT and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was analyzed using this probe. The results proved that the introduction of PCBM into P3HT does not simply make P3HT melt at a lower temperature, but rather make it have a binary eutectic melting behavior. So, these findings can provide an in situ and damage-free method to study the melting process of P3HT.

Effect of two-step annealing on the performance of ternary polymer solar cells based on P3HT:PC71BM:SQ

The effect of two-step annealing, including solvent annealing and further-step thermal annealing on the inverted ternary polymer solar cells (PSCs), which are composed of poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM):2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (SQ), was systematically investigated. The film morphology of ternary blends was characterized by X-ray diffraction and atomic force microscope. The results showed that a dramatic enhancement of power conversion efficiency from 1.32% to 4.42% was obtained due to the improved light harvesting, optimized self-assembled morphology and thermally induced crystallization of ternary blends. Especially, the optimized temperature of the thermal annealing process was remarkably decreased to 80°C. It was also found that the two-step annealing process was crucial in achieving high performance, which could not only control the domain size of SQ but also maintain a well-ordered nanoscale structure within the ternary blends of P3HT:PC71BM:SQ.

Multi-branched CdSe nanocrystals stabilized by weak ligand for hybrid solar cell application.

In this article, multi-branched CdSe nanocrystals were produced by a facile colloidal approach stabilized by oleylamine at a relative low temperature. The as-prepared multi-branched CdSe nanocrystals after simple washing process were used in the fabrication of poly(3-hexylthiophene)/CdSe bulk heterojunction photovoltaic device. The effective charge separation in the poly(3-hexylthiophene)/ CdSe nanocomposites have been confirmed by the strong photoluminescence quenching. The films of the blends of P3HT and simply-washed CdSe nanocrystals show more uniform morphology and flatter surface than the film of the bends of P3HT and pyridine-refluxed CdSe nanocrystals. The corresponding power conversion efficiency under 1 sun is about 0.66% for the P3HT/pyridine-washed CdSe hybrid device. Our work did a preliminary study in the hybrid solar cell application of branched blenze CdSe nanocrystals prepared by an easier way, and will be interesting and helpful for making the high-efficiency hybrid solar cells with branched CdSe acceptors.

Best of Both Worlds: Conjugated Polymers Exhibiting Good Photovoltaic Behavior and High Tensile Elasticity

This paper examines a series of poly(3-alkylthiophene)s (P3ATs), a class of materials for which mechanical compliance and electronic performance have been observed to be in competition. P3ATs with longer alkyl side chains (n ≥ 8) have high elasticity and ductility, but poor electronic performance (as manifested in photovoltaic efficiency in blends with fullerenes); P3ATs with shorter chains (n ≤ 6) exhibit the opposite characteristics. A series of four polymer films in which the average length of the side chain is n = 7 is tested using mechanical, spectroscopic, microscopic, and photovoltaic device-based measurements to determine whether or not it is possible, in principle, to maximize both mechanical and electronic performance in a single organic semiconductor (the “best of both worlds”). The four polymer samples are (1) a physical blend of equal parts P3HT and P3OT (P3HT:P3OT, n = 6 and n = 8), (2) a block copolymer (P3HT-b-P3OT), (3) a random copolymer (P3HT-co-P3OT), and (4) poly(3-heptylthiophene) (P3HpT, n = 7). The tensile moduli obtained by mechanical buckling correlate well with spectroscopic evidence (using the weakly interacting H aggregate model) of a well-ordered microstructure of the polymers. The block copolymer was the stiffest of the hybrid samples (680 ± 180 MPa), while P3HpT exhibited maximum compliance (70 ± 10 MPa) and power conversion efficiency in a 1:1 blend with the fullerene PC61BM using stretchable electrodes (PCE = 2.16 ± 0.17%) that was similar to that of P3HT:PC61BM. These analyses may permit the design of organic semiconductors with improved mechanical and electronic properties for mechanically robust and stretchable applications.

Tuning the Organic Solar Cell Performance of Acceptor 2,6-Dialkylaminonaphthalene Diimides by Varying a Linker between the Imide Nitrogen and a Thiophene Group

Core-substituted naphthalene diimides (NDI) are promising candidates as acceptors for organic solar cells. To study their structure–property relationships, a series of 2,6-dialkylamino-NDI compounds with various substituents were synthesized, characterized, and tested in bulk heterojunction solar cells by blending with regioregular poly(3-hexylthiophene) (P3HT). The imide substituents consisted of a linker connected to a thiophene group, where the linker was phenyl, methyl, or ethyl. The core substituents were cyclohexylamino or 2-ethylhexylamino. While the various substituents had little effect on the optoelectronic properties in solution, they strongly affected device performance and blend morphology. Under the conditions studied, the best performance was obtained with the methyl linker combined with the cyclohexylamino core substituent, with a power conversion efficiency of 0.48% and a high open circuit voltage of 0.97 V. For blends of P3HT with modified NDI non-fullerene acceptors, the methyl linker promoted larger phase-separated domains than the ethyl or phenyl linkers. DFT calculations showed that the linker determines the orientation of the thiophene conjugated plane with respect to the NDI conjugated plane. That angle was 114°, 45°–61°, and 8° for the methyl, phenyl, and ethyl linkers, respectively. Using thiophene at the end of the imide substituent adds a unique dimension to tune morphology and influence the molecular heterojunction between donor and acceptor.

Synthesis of All-Conjugated ABA and AB-type Donor-Acceptor Block Copolymers and Their Application in All-Polymer Solar Cells

ABSTRACTIn this work, we report the synthesis of all-conjugated donor-acceptor block copolymers via a externally initiated Kumada catalyst-transfer polycondensation (KCTP) method. In the first step, electron acceptor blocks, poly(naphthalene diimide)s (PNDIs), were prepared via the Stille coupling polycondensation. Then, P3HT blocks were polymerized by KCTP initiated by Ni(COD)2 activated PNDI complexes. Therefore, a series of ABA (P3HTs were initiated from both ends of PNDI) and AB-type (P3HT was initiated from one end of PNDI) block copolymers were successfully synthesized. Before fabrication of all-polymer solar cells, the morphologies and crystalline behaviors of the block copolymers were extensively investigated as a function of thermal annealing and the main chain composition of PNDI block. As a control, the crystalline behaviors of the physical blends of P3HT and PNDIs were also reported. Finally, all-polymer solar cells were fabricated by using the block copolymers as the single active component or as surfactants. A PCE of 0.11 % with Voc=0.46 V, Jsc=0.50 mA/cm2, and FF=0.46 was recorded by using the donor-acceptor all-conjugated block copolymer as the single active component.

Guided crystallization of P3HT in ternary blend solar cell based on P3HT:PCPDTBT:PCBM

In ternary blend of P3HT:PCPDTBT:PC61BM, bundles of well-defined P3HT fibrils formed a network in a matrix comprised of a mixture of P3HT, PCPDTBT and PCBM yielding a 27% improvement in device efficiency.

In situ modulation of the vertical distribution in a blend of P3HT and PC60BM via the addition of a composition gradient inducer

2,2,3,3,4,4,4-Heptafluoro-N-phenyl-butyr-amide (F-ADD) was synthesized and shown to induce a composition gradient in a blend of P3HT and PC60BM. The addition of small amounts (ca. 0.5 wt%) of F-ADD modulated the chemical distribution in the blend along the vertical direction by controlling the blend component interface energy through selective interactions between F-ADD and PC60BM. A homogeneous compositional distribution along the vertical direction in the nanostructured bulk heterojunction (BHJ) increased the interfacial area, which shortened the exciton path length to the donor-acceptor interface and improved the photovoltaic performance.

Highly efficient and high transmittance semitransparent polymer solar cells with one-dimensional photonic crystals as distributed Bragg reflectors

We demonstrate that one-dimensional photonic crystals as distributed Bragg reflectors can effectively improve the performance of semitransparent polymer solar cells (PSCs) based on the blend of P3HT:ICBA. The one dimensional distributed Bragg reflectors (1D DBRs) are composed of N pairs of WO3/LiF which are thermally evaporated on Ag anode. Due to its photonic bandgap, 1D DBRs can reflect the light totally back into the PSCs when the high reflectance range of 1D DBRs is well matched with absorption spectrum of the active layer. A maximum power conversion efficiency (PCE) of 4.12%, a highest transmittance of 80.4% at 660nm and an average transmittance of 55.6% in the wavelength range of 600–800nm are obtained in the case of N=8, corresponding enhancement of 24.1% in PCE when compared with the device without the 1D DBRs.

Charge Generation Dynamics in CdS:P3HT Blends for Hybrid Solar Cells.

Development of design rules for hybrid inorganic-organic solar cells through understanding charge generation and recombination dynamics is an important pathway for the improvement of solar cell conversion efficiencies. In this Letter, we study the dynamics of charge generation in CdS:polymer blends by transient absorption spectroscopy. We show that charge generation following excitation of the inorganic component is highly efficient and can occur up to a few nanoseconds after excitation, allowing for diffusion of charges within the inorganic component to an interface. In contrast, charge generation following excitation of the organic component occurs on subpicosecond time scales but suffers from two loss processes, incomplete exciton dissociation and geminate recombination.