Efficiency-improved organic solar cells based on plasticizer assisted soft embossed PEDOT:PSS layers.
ABSTRACT Organic solar cells (OSCs) have attracted extensive attention as a promising approach for cost-effective photovoltaic devices. This study demonstrates a novel imprinting approach based on additional plasticizing, which is suited for thin polyethylenedioxythiophene:polystyrenesulphonate (PEDOT:PSS) layers. Such films are widely used as electron blocking and hole collecting intermediate layers in OSCs. Master molds with nano-scale channels are used for the temperature and pressure assisted imprinting routine and the shape of the imprinted structures is easily tunable via the plasticizer concentration. Depending on the surface topology of the PEDOT:PSS films structured poly(3-hexylthiophene) (P3HT):phenyl-C(61)-butyric acid methyl ester (PCBM) bulk heterojunction solar cells have improved power conversion efficiencies in comparison to their planar references. This effect results from enhanced optical absorption due to the resulting textured aluminum electrode and improved charge carrier extraction at the artificially structured electrodes. In addition, OSCs based on low aspect ratio PEDOT:PSS imprints show increased relative performance under oblique light incidence.
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ABSTRACT: We present a new water-vapour-assisted nanoimprint lithography (NIL) process for the patterning of the conducting poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The process was optimized with respect to relative humidity, applied pressure and temperature (RH, p, T). The control of environmental humidity was found to be crucial. High quality nanostructures were reproducibly obtained at high relative humidity values (≥75%), with sub-100 nm resolution features attaining aspect ratios as high as 6 at 95% RH. The developed process of water-vapour-assisted NIL (WVA-NIL) strongly affects the electronic properties of PEDOT:PSS. By current-voltage measurements and ultraviolet photoemission spectroscopy we demonstrate that the process parameters p, T and RH are correlated with changes of PEDOT:PSS conductivity, work function and states of the valence band. In particular, an increase in the films conductivity by factors as high as 105 and a large decrease in the work function, up to 1.5 eV, upon WVA-NIL processing were observed. Employed as anode buffer layer in P3HT:ICBA bulk heterojunction solar cells, PEDOT:PSS processing was found to affect significantly the devices performance.RSC Advances 07/2014; 4(64). DOI:10.1039/C4RA04807E · 3.71 Impact Factor
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ABSTRACT: In this work, we investigate the effect of the thickness of the polyethylenimine ethoxylated (PEIE) interface layer on the performance of two types of polymer solar cells based on inverted poly(3-hexylthiophene) (P3HT): phenyl C61-butryricacid methyl ester (PCBM) and thieno[3,4-b]thiophene/ benzodithiophene (PTB7): [6,6]-phenyl C71-butyric acidmethyl ester (PC71BM). Maximum power conversion efficiencies of 4.18% and 7.40% are achieved at a 5.02 nm-thick PEIE interface layer, for the above-mentioned solar cell types, respectively. The optimized PEIE layer provides a strong enough dipole for the best charge collection while maintaining charge tunneling ability. Optical transmittance and atomic force microscopy measurements indicate that all PEIE films have the same high transmittance and smooth surface morphology, ruling out the influence of the PEIE layer on these two parameters. The measured external quantum efficiencies for the devices with thick PEIE layer are quite similar to that of the optimized device, indicating the poor charge collection ability of thick PEIE layers. The relative low performance of devices with a PEIE layer of thickness less than 5 nm is the result of weak dipole and partial coverage of the PEIE layer on ITO.Physical Chemistry Chemical Physics 09/2014; 16(43). DOI:10.1039/C4CP03484H · 4.20 Impact Factor
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ABSTRACT: Living organisms use fractal structures to optimize material and energy transport across regions of differing size scales. Here we test the effect of fractal silver electrodes on light distribution and charge collection in organic semiconducting polymer films made of P3HT and PCBM. The semiconducting polymers were deposited onto electrochemically grown fractal silver structures (5,000 nm x 500 nm; fractal dimension of 1.71) with PEDOT:PSS as hole-selective interlayer. The fractal silver electrodes appear black due to increased horizontal light scattering, which is shown to improve light absorption in the polymer. According to surface photovoltage spectroscopy, fractal silver electrodes outperform the flat electrodes when the BHJ film thickness is large (> 400 nm, 0.4 V photovoltage). Photocurrents of up to 200 microamperes cm-2 are generated from the bulk heterojunction (BHJ) photoelectrodes under 435 nm LED (10-20 mW cm-2) illumination in acetonitrile solution containing 0.005 M ferrocenium hexafluorophosphate as the electron acceptor. The low IPCE values (0.3-0.7%) are due to slow electron transfer to ferrocenium ion and due to shunting along the large metal-polymer interface. Overall, this work provides an initial assessment of the potential of fractal electrodes for organic photovoltaic cells.08/2014; 2(39). DOI:10.1039/C4TA03204G