Spray deposition of poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester blend under electric field for improved interface and organic solar cell characteristics (original) (raw)
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Journal of Physical Chemistry C, 2009
The effect of the polymer-electrode interface on the photovoltaic performance of poly(3-hexylthiophene): phenyl-C61-butyric acid methyl ester based solar cells was investigated. Four forms of cathodes, Ca/Ag, Ca/Al, LiF/Al, and Al, were deposited on photoactive films. The Ca/Al cathode showed the best FF of 0.69, while Al produced the worst one of 0.55. The efficiency-limiting effect, a concavity in the fourth quadrant of the current-voltage characteristics, can be caused by a thermally degraded poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) anode or an oxidized Ca cathode. An inorganic material interlayer of CdSe between the photoactive layer and the cathode can, to some extent, inhibit the negative effect of polymer-metal interface.
Solar Energy Materials and Solar Cells, 2010
We have systematically investigated the morphology of poly(3-hexylthiophene; P3HT) and [6,6]phenyl C 61-butyic acid methyl ester (PCBM) blend films prepared through a slow growth apparoch as a function of PCBM loading in the blends for bulk heterojunction solar cells. In addition to the electrical characterisitcs, the molecular ordering and crystallinity of the polymers was examined by using the UV-vis spectroscopy and grazing incidence X-ray diffraction. From the images of confocal laser scan microscopy, we were also able to in-situ monitor the phase separation of the P3HT:PCBM blends during the process of solvent evaporation. Finally, the conductive atomic force microscopy was utilized to probe the spatial distribution of the local current across the photoactive layer prepared with various P3HT:PCBM ratios. From the experimental results, we found that the distribution of PCBM molecules in the P3HT matrix became homogeneous after the solvent annealing process, even though the distribution of the PCBM molecules was not even in the beginning. Therefore, the higher device efficiency could be attributed to the better thin-film morphology of the polymer blends.
P3HT/PCBM bulk heterojunction organic photovoltaics: Correlating efficiency and morphology
Nano letters, 2011
Controlling thin film morphology is key in optimizing the efficiency of polymer-based photovoltaic (PV) devices. We show that morphology and interfacial behavior of the multicomponent active layers confined between electrodes are strongly influenced by the preparation conditions. Here, we provide detailed descriptions of the morphologies and interfacial behavior in thin film mixtures of regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM), a typical active layer in a polymer-based PV device, in contact with an anode layer of PEDOT-PSS and either unconfined or confined by an Al cathode during thermal treatment. Small angle neutron scattering and electron microscopy show that a nanoscopic, bicontinuous morphology develops within seconds of annealing at 150°C and coarsens slightly with further annealing. P3HT and PCBM are shown to be highly miscible, to exhibit a rapid, unusual interdiffusion, and to display a preferential segregation of one component to the electrode interfaces. The ultimate morphology is related to device efficiency.
Topographical and morphological aspects of spray coated organic photovoltaics
Organic Electronics, 2009
Herein we discuss the topographical and nanomorphological aspects of spray deposited organic photovoltaics. We show that the solvent properties have a massive impact on the topography, but less on the nanomorphology formation of composites based on the electron donor poly(3-hexylthiophene) (P3HT) and the electron acceptor [6,6]-phenyl C61 butyric acid methyl ester (PCBM). An adapted solvent mixture consisting of orthodichlorobenzene (oDCB) and 1,3,5-trimethylbenzene (mesitylene) allows us to demonstrate spray coated organic photovoltaic devices with 3.1% power conversion efficiency (PCE). Moreover, we show that spray coating is a feasible technology to deposit all solution processable layers of organic solar cells, including the hole transporting layer poly(3,4-ethylene dioxythiophene) doped with polystyrene sulphonic acid (PEDOT:PSS) as well and demonstrate fully spray coated devices with 2.7% PCE.
Superlattices and Microstructures, 2014
Charge carrier diffusion and recombination in an absorber blend of poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl C 70 -butyric acid methyl ester (PCBM) with indium tin oxide (ITO) and aluminum contacts have been analyzed by means of impedance spectroscopy. The capacitance exhibits Mott-Schottky behavior indicating the formation of a Schottky junction (band bending) at the P3HT:PCBM/Al interface. Built-in potential of 0.88 V and acceptor impurities concentrations of 9.3 Â 10 15 cm 3 was calculated through capacitance measurements. Impedance measurement shows, at high frequency, an inclined straight line indicates the inhomogeneous nature of the electrode-organic interface. On the other hand, the arc localized at low-frequency is attributed to recombination in the photoactive blend. Global mobility is in the range of 1.1-1.4 Â 10 À3 cm 2 V À1 s À1 , which is slightly higher as compared to the literature.
Journal of Applied Physics, 2005
Regioregular poly͑3-hexylthiophene͒ ͑RR-P3HT͒ is a promising candidate for polymer photovoltaic research due to its stability and absorption in the red region. In this manuscript, we report polymer photovoltaic devices based on RR-P3HT:methanofullerene ͓6,6͔-phenyl-C 61 -butyric acid methyl ester ͑PCBM͒ 1:1 weight-ratio blend. We studied the effects of annealing temperature and time on the device performance for devices annealed before and after cathode deposition. Thermal annealing shows significant improvement in the performance for both types of annealing conditions, with postproduction annealing being slightly better. For devices with a 43-nm-thick active layer, maximum power conversion efficiency ͑PCE͒ of 3.2% and fill factor up to 67% is achieved under Air Mass 1.5, 100-mW/ cm 2 illumination. We performed atomic force microscopy and ultraviolet-visible absorption spectroscopy on the P3HT:PCBM films to explain the effect of thermal annealing. By keeping the optimized thermal annealing condition and by varying the active layer thickness, we fabricated devices with PCE up to 4.0%, which is the highest efficiency reported so far for this system.
The Consequences of Interface Mixing on Organic Photovoltaic Device Characteristics
Advanced Functional Materials, 2011
Organic bulk-heterojunction solar cells are being developed as a low-cost alternative to inorganic photovoltaics. A key step to producing high-efficiency bulk-heterojunction devices is film curing using either heat or a solvent atmosphere. All of the literature examining the curing process have assumed that improvement of the bulk-heterojunction morphology is the reason for the increased filling factor, short-circuit current density, and efficiency following heat or solvent treatment. We show in this article that heat treatment causes the donor polymer (P3HT) and polymer electrode (PEDOT:PSS) to mix physically to form an interface layer. This interface layer is composed of a mixture of P3HT and PSS in which the P3HT is oxidized to P3HT + . This mixed layer affects the open-circuit voltage and compensation voltage by limiting the dark current. This result implies that a simplistic description of the P3HT/PEDOT:PSS contact as a sharp interface between bulk P3HT and bulk PEDOT:PSS cannot adequately capture its electrical characteristics.
2017
Organic solar cells (OSCs) have attracted a significant attention during the last decade due to their simple processability on a flexible substrate as well as scope for large-scale production using role to role technique. Improving the performance of the organic solar cells and their lifetime stability are one of the main challenges faced by researchers in this field. In this thesis, work has been carried out using a blend of Poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-Phenyl C6i butyric acid methyl ester (PCBM) as an active layer in the ratio of (1:1) (P3HT:PCBM). The efficiency and stability of P3HT:PCBM-based solar cells have been examined using different methods and employing novel materials such asl-[N-(2-ethoxyethyl) pent-4-ynamide]-8 (11), 15 (18), 22 (25)tris-{2-[2-(2-ethoxyethoxy) ethoxy]-l-[2-((2-ethoxyethoxy)-ethoxy) methyl] ethyloxy] phthalocyaninato zinc (II) (ZnPc) to construct a ternary hybrid as the active layer. Controlling the morphology and crystallinity of P3HT:PCBM active layer was carried out using different solvents including chloroform (CF), chlorobenzene (CB) and dichlorobenzene (DCB) and their co-solvents in the ratio of (1:1) to dissolve the P3HT:PCBM blend. Optimum morphology and crystallinity were achieved using a co-solvent made of CB:CF with the obtained solar cell exhibiting the highest performance with PCE reaching 2.73% among other devices prepared using different solvents. Further device performance improvement was observed through optimization of active layer thickness with studied thickness falling in range 65-266 nm. Measurements of the PV characteristics of the investigated OSC devices have revealed optimum performance when active layer thickness was 95 nm with PCE=3.846%. The stability of the P3HT:PCBM-based devices on optimisation of the active layer thickness has shown a decrease in PCE of about 71% over a period of 41 days. Furthermore, P3HT has been blended with different fullerene derivatives (PC60BM, PC6iBM, PC70BM and PC71BM) and the active layers were processed using the optimum solvent as well as optimum film's thickness. These PCBM derivatives have different lower unoccupied molecular level (LUMO) and different higher occupied molecular level (HOMO) positions, which subsequently influence the PV parameters of the OSCs such as the device open circuit voltage (V oc) and its built-in potential (V b i). P3HT:PC6iBM-based blend has exhibited the highest device performance with PCE reaching 4.2%. Using the above mentioned optimum parameters, the P3HT:PCBM-based devices have been subjected to post-deposition annealing at different temperatures in the range 100-180°C. Efficient device performance was ascribed to P3HT:PCBM layers being subjected to post-deposition heat treatment at 140°C with PCE=5.5%. Device stability as a result of post-deposition heat treatment has also been shown to improve with PCE degrading by about 38% after 55 days.