Jang Jo

Plasmon enhanced performance of organic solar cells using electrodeposited Ag nanoparticles

To enhance solar harvesting in organic solar cells, uniform-sized metal nanoparticles of ∼13 nm were incorporated to the device via pulse-current electrodeposition, which is a kind of simple and quick solution process that can control the density and size of metal nanoparticles. By incorporating plasmonic Ag nanoparticles on surface modified transparent electrodes, overall power conversion efficiency was increased from 3.05% to 3.69%, mainly resulting from the improved photocurrent density as a result of enhanced absorption of the photoactive conjugate polymer due to the high electromagnetic field strength in the vicinity of the excited surface plasmons.

Fabrication of organic bulk heterojunction solar cells by a spray deposition method for low-cost power generation

The authors report on a spray deposition method as a cost-efficient technique for the fabrication of organic solar cells (OSCs). Active layers of OSCs were fabricated using conventional handheld airbrushes. Although the spray deposited film showed a relatively rougher surface than spin coated ones, pinhole-free and constant thickness films could be obtained. An optimized OSC showed 2.83% of power conversion efficiency and 52% of incident photon to current conversion efficiency even though the device was fabricated in air. The performance of sprayed OSCs was comparable to that of the spin coated devices fabricated in air.

Control of the electrode work function and active layer morphology via surface modification of indium tin oxide for high efficiency organic photovoltaics

Indium tin oxide (ITO) substrates modified with self-assembled monolayers (SAMs) were used to control the anode work function and active layer morphology of organic solar cells based on poly(3-hexylthiophene)/[6:6]-phenyl-C61 butyric acid methyl ester heterojunctions. By using SAMs with the terminal groups –NH2, –CH3, and –CF3, the authors were able to control the hole injection barrier of the ITO closer to the highest occupied molecular orbital level of active layer and surface energy of the ITO substrate. A solar cell device with CF3 SAM treated ITO was found to exhibit high efficiency performance, about 3.15%.

Surface relief gratings on poly(3-hexylthiophene) and fullerene blends for efficient organic solar cells

The use of periodic submicrometer structures as an efficient light-trapping scheme was investigated for high performance organic solar cells (OSCs) based on poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61. The gratings on an active layer are achieved by a soft lithographic approach using photoinduced surface-relief gratings (SRGs) on azo polymer films and poly(dimethylsiloxane) as a master and stamp, respectively. Incident photon to current conversion efficiency and the power conversion efficiency of OSC with gratings increased primarily due to enhanced short circuit current density, indicating that SRGs induce further photon absorption in active layers by increasing the optical path length and light trapping.

Factors to be Considered in Bulk Heterojunction Polymer Solar Cells Fabricated by the Spray Process

One of the attractions of solution-processed polymer solar cells (PSCs) is the potential for low-cost production by high-throughput roll-to-roll processes. The spray process can be suggested as an elegant alternative for PSCs fabrication due to its high production speed. We highlight the effects of sprayed droplet sizes on the film topography and drying time of droplets. We relate the latter to the PSCs device performances. The transfer efficiency and deposition rate of the spray process as a function of the droplet size are investigated for the high production speed and lowering the cost. PSC device fabrication with an optimized spray-operating condition yielded a power conversion efficiency of 3.4%. The comparable efficiency of PSCs fabricated by a roll-to-roll compatible process compared to spin-coated one achieved in this paper brings these devices one step closer to the realization of low-cost PSCs production.

A morphology controller for high-efficiency bulk-heterojunction polymer solar cells

Controlling the morphology in bulk-heterojunction solar cells is the preferred and most effective way to achieve high efficiency. To control the morphology, we synthesized a novel hydrophobic end-functionalized P3HT to induce hydrophilic–hydrophobic repulsive interactions in the boundary between the relatively hydrophilic PCBM and the relatively hydrophobic P3HT. The introduction of hydrophobic end-functionalized P3HT (F-P3HT) leads to larger PCBM clusters, while maintaining the crystallinity of P3HT due to repulsive interactions. F-P3HT thus provides a maximized continuous interfacial area between the donor and the acceptor as well as bi-continuous networks of donor and acceptor domains, resulting in better percolation pathways for charge transport.

Effect of photo- and thermo-oxidative degradation on the performance of hybrid photovoltaic cells with a fluorene-based copolymer and nanocrystalline TiO2

This work proposes a new fluorene-based copolymer containing a spiroanthracenefluorene unit, poly[10,10-bis(2-ethylhexyl)-10H-spiro(anthracene-9,9′-fluorene)-2′,7′-diyl-co-bithiophene] (SFT2), for hole transporting materials in photovoltaic (PV) cells consisting of conjugated polymers and nanocrystalline TiO2. This polymer was synthesized to avoid photo- and thermo-oxidative degradation of poly[9,9′-dioctyl-fluorene-co-bithiophene] (F8T2) used in hybrid PV cells. The occurrence of oxidative degradation after irradiation with simulated sunlight or severe heating over the glass transition temperature in air on F8T2 and SFT2 films was confirmed by an increase of low energy emission at 600 nm in the photoluminescence emission spectra—originating from the generation of a keto defect site in the C-9 position of the fluorene units. In conclusion, we found that the defects play a vital role in degradation of the device performance of PV cells, especially in the decline of short-circuit current density (Jsc), consisting of fluorene-based polymers.

Perfluorocyclobutane containing polymeric gate dielectric for organic thin film transistors with high on/off ratio

A thermally cross-linkable perfluorocyclobutane (PFCB) polymer was synthesized and examined for use as the gate dielectric in organic thin film transistors (OTFTs). The PFCB polymer showed good solvent and process resistance during the photolithographic patterning of the electrodes. Bottom contact OTFTs were fabricated with poly(3-hexylthiophene)-2,5-diyl (P3HT) as the semiconductor, either spin cast or dip coated, on the PFCB gate dielectric. OTFTs fabricated with dip-coated P3HT showed a field effect mobility of 1.8×10−3cm2∕Vs and a high on/off current ratio of 8.3×106 in the saturation regime, with a source-drain voltage of VD=−50V.