Influence of a ternary donor material on the morphology of a P3HT:PCBM blend for organic photovoltaic devices (original) (raw)
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ACS applied materials & interfaces, 2015
The use of solvent additives in the fabrication of bulk heterojunction polymer:fullerene solar cells allows to boost efficiencies in several low bandgap polymeric systems. It is known that solvent additives tune the nanometer scale morphology of the bulk heterojunction. The full mechanism of efficiency improvement is, however, not completely understood. In this work, we investigate the influences of blend composition and the addition of 3 vol % 1,8-octanedithiol (ODT) as solvent additive on polymer crystallization and both, vertical and lateral morphologies of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] and [6,6]-phenyl C71-butyric acid methyl ester (PCPDTBT:PC71BM) blend thin films processed from chlorobenzene-based solutions. The nanoscale morphology is probed with grazing incidence small- and wide-angle X-ray scattering as well as X-ray reflectivity and complemented with UV/vis spectroscopy. In PCPDTBT:PC71BM films...
2012
Recent work has shown that poly(3-hexylthiophene) (P3HT) and the surface-functionalized fullerene 1-(3-methyloxycarbonyl)propyl(1-phenyl[6,6])C 61 (PCBM) are much more miscible than originally thought, and the evidence of this miscibility requires a return to understanding the optimal morphology and structure of organic photovoltaic active layers. This manuscript describes the results of experiments that were designed to provide quantitative thermodynamic information on the miscibility, interdiffusion, and depth profile of P3HT : PCBM thin films that are formed by thermally annealing initial bilayers. It is found that the resultant thin films consist of a 'bulk' layer that is not influenced by the air or substrate surface. The composition of PCBM in this 'bulk' layer increases with increased PCBM loading in the original bilayer until the 'bulk' layer contains 22 vol% PCBM. The introduction of additional PCBM into the sample does not increase the amount of PCBM dispersed in this 'bulk' layer. This observation is interpreted to indicate that the miscibility limit of PCBM in P3HT is 22 vol%, while the precise characterization of the depth profiles in these films shows that the PCBM selectively segregates to the silicon and near air surface. The selective segregation of the PCBM near the air surface is ascribed to an entropic driving force.
The Effect of Fullerene Derivatives Ratio on P3HT-based Organic Solar Cells
Energy Procedia, 2015
The effect of fullerene ratio PCBM and ICBA on the P3HT-based solar cells were investigated under ambient conditions; the ratio was varied in the range of 1-3. The optical, morphological, structural, and electrical characteristics were investigated both in dark and under illumination. The absorption spectra have revealed a decrease in the intensities by increasing the fullerene ratio and the peaks were blue shifted. Moreover, florescence spectra demonstrated charge transfer from P3HT to fullerene molecules due to uniform distribution of fullerene domains within the P3HT matrix. XRD patterns have shown a strong reduction in the crystallinity by increasing the ratio of fullerene within the blend. Furthermore, AFM images showed smother surface corresponding to pinholes with higher ratio while rougher surface with lower fullerene ratio was observed. The best performance was recorded for P3HT:PCBM (3:1) with VOC = 0.58 volt, JSC = 9.9 mA.cm-2 and PCE 1.82%. The fill factor (FF) was found to be small for all studied samples which could be associated with the preparation conditions where all samples were prepared under normal ambient. Devices which demonstrated best performance were attributed to improved crystallinity and enhanced light absorption of the active layer.
Polymer Chemistry, 2015
A new D–A structured conjugated polymer (PBDO-T-TDP) based on electron-rich benzo[1,2-b:4,5-b’] difuran (BDO) containing conjugated alkylthiophene side chains with an electron-deficient diketopyrrolopyrrole (DPP) derivative is designed and synthesized. The polymer shows a narrow band gap with broad UV-Visible absorption spectra, which is in contrast to that of the P3HT:PCBM binary blend. Furthermore, its energy levels can meet the energetic requirement of the cascaded energy levels of P3HT and PCBM. Therefore, PBDO-T-TDP is used as a sensitizer in P3HT:PCBM based BHJ solar cells and its effect on their photovoltaic properties was investigated by blending them together at various weight ratios. It is observed that the resulting ternary blend system exhibited a significant improvement in the device performance (ŋ 3.10%) as compared with their binary ones (ŋ 2.15%). Such an enhancement in the ternary blend system is ascribed to their balanced hole and electron mobility along with uniform distribution of PBDO-T-TDP in the blend system, as revealed by organic field effect transistors and AFM studies.
The European Physical Journal Applied Physics, 2011
The nanostructure of the active layer in polymer/fullerene bulk heterojunction solar cells is known to have a strong impact on the device performances. Controlling the polymer/fullerene blend morphology is therefore particularly important. In this work, a rod-coil block copolymer, based on a regio-regular poly(3-hexylthiophene) electron-donor rod block and a C 60-grafted coil block, is used as compatibilizer and its influences on the thin film morphology as well as the photovoltaic performances are investigated. It is shown that a small fraction of compatibilizer can enhance the device performances in an otherwise nonoptimized process. At higher fractions or long annealing times however, the fullerene-grafted copolymer is found to behave as a nucleation center and triggers the formation of fullerene crystals.
Scientific Reports, 2014
We have used Soxhlet solvent purification to fractionate a broad molecular weight distribution of the polycarbazole polymer PCDTBT into three lower polydispersity molecular weight fractions. Organic photovoltaic devices were made using a blend of the fullerene acceptor PC 71 BM with the molecular weight fractions. An average power conversion efficiency of 5.89% (peak efficiency of 6.15%) was measured for PCDTBT blend devices with a number average molecular weight of M n 5 25.5 kDa. There was significant variation between the molecular weight fractions with low (M n 5 15.0 kDa) and high (M n 5 34.9 kDa) fractions producing devices with average efficiencies of 5.02% and 3.70% respectively. Neutron reflectivity measurements on these polymer:PC 71 BM blend layers showed that larger molecular weights leads to an increase in the polymer enrichment layer thickness at the anode interface, this improves efficiency up to a limiting point where the polymer solubility causes a reduction of the PCDTBT concentration in the active layer.
Effect of polydispersity on the bulk-heterojunction morphology of P3HT:PCBM solar cells
Journal of Polymer Science Part B: Polymer Physics
Bulk heterojunctions (BHJ) based on semiconducting electron-donor polymer and electronacceptor fullerene have been extensively investigated as potential photoactive layers for organic solar cells (OSCs). In the experimental studies, poly-(3-hexyl-thiophene) (P3HT) polymers are hardly monodisperse as the synthesis of highly monodisperse polymer mixture is a near impossible task to achieve. However, the majority of the computational efforts on poly-(3-hexylthiophene): phenyl-C61-butyric acid methyl ester (P3HT:PCBM) based OSCs, a monodisperse P3HT is usually considered. Here, results from coarse-grained molecular dynamics (CGMD) simulations of solvent evaporation and thermal annealing process of the BHJ are shared describing the effect of variability in molecular weight (a.k.a. polydispersity) on the morphology of the active layer. Results affirm that polydispersity is beneficial for charge separation as the interfacial area is observed to increase with higher dispersity. Calculations of percolation and orientation tensors, on the other hand, reveal that a certain polydispersity index (PDI) ranging between 1.05-1.10 should be maintained for optimal charge transport. Most importantly, these results point out that the consideration of polydispersity should be considered in computational studies of polymer based organic solar cells.
Synthetic Metals, 2011
The use of carbon nanotube-fullerene hybrid additives to the standard P3HT:PCBM blend bulkheterojunction organic photovoltaic device is presented. The effects of incorporating single-wall carbon nanotubes, functionalized with linked C 60 molecules by amination on device characteristics are detailed. The concentration of the carbon nanotube-fullerene hybrid in the active layer blend was varied to ascertain their cumulative impact on device performance in terms of open circuit voltage, short circuit current, fill factor and efficiency. We found that decreasing the length of the carbon nanotubes to ∼60 nm through fluorination and subsequent thermal treatment was beneficial in terms of eliminating shorted devices allowing much improved diode formation. A trend of improving device performance as a function of concentration of the carbon nanotube-hybrids in a heterojunction of P3HT:PCBM was observed.