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.
"In order to induce greater light absorption in the photoactive layer, nano-patterning is often applied to the metal-oxide buffer layer, which functions as the electron extraction/transportation layer. Not only on metal-oxide buffer layer, plasticizer assistied soft embossing (PASE) structure have been applied on PEDOT:PSS hole extracting layer to improve solar cell performance17. For P3HT:PCBM solar cells based on PASE structured PEDOT:PSS layers the averaged overall power efficiency is improved by up to 18%. "
[Show abstract][Hide abstract] ABSTRACT: In order to induce greater light absorption, nano-patterning is often applied to the metal-oxide buffer layer in inverted bulk-heterojunction(BHJ) solar cells. However, current homogeneity was significantly disturbed at the interface, leading to an efficiency that was not fully optimized. In this work, an additional PC61BM layer was inserted between the ZnO ripple and the photoactive layer to enhance the electron extraction. The insertion of additional PC61BM layer provided substantial advantages in the operation of inverted BHJ solar cells; specifically, it enhanced current homogeneity and lowered accumulation and trapping of photogenerated charges at the ZnO interface. Inclusion of the additional PC61BM layer led to effective quenching of electron-hole recombination by a reduction in the number of accumulated charges at the surface of ZnO ripples. This resulted in a 16% increase in the efficiency of inverted BHJ solar cells to 7.7%, compared to solar cells without the additional PC61BM layer.
[Show abstract][Hide abstract] ABSTRACT: Thin photoactive polymer blend films of poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(5-(2-(ethylhexyloxy)-2-methoxycyanoterephthalyliden) (MEH-CN-PPV) are investigated. The morphology is probed as a function of blend ratio (21, 28, 44, 54, and 70 wt % P3HT) and annealing using imaging techniques and soft X-ray scattering. The surface structure is detected with optical microscopy and atomic force microscopy (AFM), the inner film morphology and the near-surface structure with grazing incidence resonant soft X-ray scattering (GI-RSoXS) using different X-ray energies. Characteristic lateral structures determined with GI-RSoXS are in agreement with AFM observations and complemented with optical microscopy. The topography and the inner film morphology have the same structural length scales. Grazing incidence wide-angle X-ray scattering (GIWAXS) results confirm the crystallinity of the P3HT domains, which is increasing with annealing, and shows no indication for crystallinity in MEH-CN-PPV. In addition, GIWAXS measurements reveal a blend ratio dependent orientation of P3HT crystals. Absorption and photoluminescence measurements complement the structural investigations.
[Show abstract][Hide abstract] ABSTRACT: Bulk heterojunction (BHJ) solar cells from 1,2-dichlorobenzene solution processed regio-regular poly(3-hexythiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) are prepared and investigated at different steps of the multi-layer stack build-up of the device. The inner structure is probed from the molecular to the mesoscale with grazing incidence small/wide angle X-ray scattering (GISAXS/GIWAXS) and X-ray reflectivity (XRR). The surface morphology is detected with atomic force microscopy (AFM). Therefore, an in-depth knowledge of the three-dimensional morphology of the bulk heterojunction solar cell, starting from the cleaned ITO substrate up to the final post-treated solar cell, is generated. The active layer structure is influence by the annealing as well as by the top contact deposition. Structures coarsen during the evaporation of the metal contacts. The P3HT crystal structure strongly depends on the device processing as well. These morphological changes together with the dif-fusion of aluminum atoms to the active layer are of importance for the device efficiency.
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