We prepared high conducting poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by solvent additives for using as a hole transport layer (HTL) in polymer solar cells (PSCs). PEDOT:PSS films treated with fluoro compounds of hexafluoroacetone (HFA) and hexafluoroisoproponal (HFIPA) with various concentrations show a significant enhancement in electrical conductivity without compromising optical transparency. The conductivity increased from 0.2 to 1053 and 746 S/cm after 4 vol. % HFA and 6 vol. % HFIPA treatments, respectively. The high performance of the PEDOT:PSS layer is attributed to preferential phase segregation of PEDOT:PSS with HFA and HFIPA solvent mixture treatment methods. The improved performance of PSC was dependent on the structure of organic solvents and the concentration of fluoro compounds in PEDOT:PSS solution. Using these optimized layers, conjugated PSCs with a poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5 thiophenediyl] polymer:[6,6]-phenyl-C71-butyric acid methyl esters (PCDTBT:PC 71 BM ) bulk heterojunction have been produced. The high power conversion efficiency (PCE) of 4.10% and 3.98% were observed for PEDOT:PSS films treated with 4 vol. % HFA and 6 vol. % HFIPA treatments, respectively. The obtained results show that PEDOT:PSS optimized with HFA and HFIPA organic solvents can be a very promising candidate for transparent anode buffer layer in the low cost organic solar cell devices.
Bulk heterojunction (BHJ) solar cells have made great progress during the past decade and consequently are now attracting extensive academic and commercial interest because of their potential advantages: lightweight, flexible, low cost, and high-throughput production. We report on the fabrication of poly((4,8-diethylhexyloxyl) benzo([1,2-b:4,5- b′]dithiophene)-2,6-diyl)-alt-((5-octylthieno[3,4-c]pyrrole-4,6-dione)-1,3-diyl) /[6,6]-phenyl-C71-butyric acid methyl ester blend active layer using airbrush spray coating method in different solvents. The parameters such as spraying time, substrate-nozzle distance for the deposition of active layers were analysed. Optical absorption of the active layers was analyzed using UV-visible spectral studies in the wavelength range from 300 to 800 nm. The surface morphology of the active layers deposited with different parameters was examined using Atomic Force Microscopy. The current densityvoltage (J-V) characteristics of photovoltaic cells were measured under the illumination of simulated solar light with 100 mW/cm2 (AM 1.5G) by an Oriel 1000 W solar simulator. We also notice that both the bottom-up and top-down approaches have played important roles in advancing our fundamental understanding of this new class of nanostructures. Finally we attempt to look into the future and offer our personal opinions on what the future trends will be in organic solar cell research.
Polymer solar cells (PSC’s) have received much attention as a promising clean and green energy technology and the power conversion efficiency have steadily increased. There are several ways to improve the device efficiency of PSC, such as changing the active layer, insertion of the electron transport layer and the anode buffer layer. Among the several anode buffer layer materials, Poly(3,4-Ethylenedioxythiophene):Poly(styrene sulfonate) (PEDOT:PSS) is widely used as anode buffer layer due to its high transparency in the visible region, high thermal stability and mechanical flexibility. However, PEDOT:PSS suffers a problem of low conductivity and limits the device application. In this report, we present the preparation of PEDOT:PSS hole transport layer through a secondary doping with flouro compounds such as hexafluoroacetone (HFA) and hexafluoroisoproponal (HIPA) with various concentrations by spin coating technique. High performance of the hole transport layer is attributed to preferential phase segregation of PEDOT:PSS with HFA and HIPA solvent mixture treatment method. The improved performance of PSC was dependent on the structure of organic solvents and the concentration of flouro compounds in PEDOT:PSS solution. Using these optimized buffer layer, conjugated polymer solar cells with a Poly9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3- benzothiadiazole-4,7-diyl-2,5 thiophenediyl] polymer:[6,6]-phenyl-C71-butyric acid methyl esters (PCDTBT:PC71BM) bulk heterojunction have been produced. A detailed analysis of the surface morphology and optical studies are presented. The obtained results show that PEDOT:PSS optimized with HFA and HIPA organic solvents can be a very promising candidate for transparent anode buffer layer in the low cost organic solar cell devices.
Solar energy is the most abundant and reliable source of energy and we have to provide for the multi-terawatt
challenge we are facing. In recent years organic photovoltaic's have become one of the most interesting research areas
due to their potential towards a cheap and broad applicability. We report the optical and electrical properties of
PBDTTT-CF: PC71BM bulk hetero-junction (BHJ) solar cell. The devices were prepared by spin coating technique
with the device structure of Glass/ITO/PEDOT: PSS/Active layer/Al. The ratio of polymer donor and fullerene
acceptor varied between 1:1 to 1:4. Optical absorption spectroscopy measurements of the films indicated absorption
peaks in the range from 500-800 nm which were attributed to PBDTTT-CF. The surface morphology of the active
layers deposited was examined using Atomic Force Microscopy. The current density (J)-voltage (V) characteristics of
the PBDTTT-CF: PC71BM bulk hetero-junction solar cells were studied. The devices fabricated using the selective
active layer show overall power conversion efficiency of 3%.
KEYWORDS: Thin films, Thin film solar cells, Solar cells, Composites, Heterojunctions, Organic photovoltaics, Molecules, Polymers, Fullerenes, Atomic force microscopy
Bulk heterojunction (BHJ) solar cells based on blends comprising conjugated polymers and fullerene acceptors
are the subject of considerable investigation because of their potential to enable the fabrication of low-cost devices that
convert sunlight into electricity. Recently, poly(2,7-carbazole) derivatives have gained momentum as a class of
promising alternative materials to poly(3-hexylthiophene) (P3HT) in organic solar cell applications. Among them,
poly[N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzo thiadiazole)] (PCDTBT) has a
relatively deeper highest occupied molecular orbital (HOMO) of 5.45 eV compared to the HOMO of 5.1 eV of the
P3HT. In this work we systematically study the effect of donor and acceptor ratio on the device performance of bulk
heterojunction solar cells made with blends of PCDTBT and PC71BM. We used PEDOT: PSS as a hole transport layer,
and TiOX as a hole-blocking layer in order to improve the power conversion efficiency. The current density-voltage (JV)
characteristics of photovoltaic cells were measured under the illumination of simulated solar light with 100 mW/cm2
(AM 1.5G) by an Oriel 1000 W solar simulator. The power conversion efficiency of the solar cell is more than 5%.
Organic solar cell (OSC) materials have recently gained rich attention due to capable of efficient power conversion, cost-effective, mechanically flexible and light weight solar cells. At the same time further materials developments for high performance will be necessary for commercial production of organic photovoltaics. The increase of efficiency has resulted from the low band gab materials, combination of polymer: fullerene and presence of blend micro structure. In this regard, the authors have achieved an efficient polymer solar cells based on Poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b]thiophenediyl](PTB7) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) as donor and acceptor respectively. The photocurrent active layers were fabricated by spray coating technique which enables large area, low cost solar cells. A systematic analysis of PTB7:PC71BM devices carried out with TiOx electron transport layer, Chlorobenzene (CB) and 1,8 Diiodooctane (DIO) solvents. Optical and surface characterization analysis carried out by UV-visible and AFM techniques respectively. From the J-V characteristics, the device prepared with CB+DIO mixture solvents and TiOx layer exhibits the best power conversion efficiency of 4.90%. It shows the device efficiency is one order of magnitude higher compared to that achieved with a TiOx electron transport layer and without DIO solvent. The obtained results shows that DIO cosolvent induced changes in active layer morphology down to nano scale range and the TiOx layer decrease the resistance between the active layer and electrode material.
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