Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Fabrication and processing of polymer solar cells: A review of printing and coating techniques

Stability/degradation of polymer solar cells

Low band gap polymers for organic photovoltaics

Organic photovoltaics (OPVs) evolve in an exponential manner in the two key areas of efficiency and stability. The power conversion efficiency (PCE) has in the last decade been increased by almost a factor of ten approaching 10%. A main concern has been the stability that was previously measured in minutes, but can now, in favorable circumstances, exceed many thousands of hours. This astonishing achievement is the subject of this article, which reviews the developments in stability/degradation of OPVs in the last five years. This progress has been gained by several developments, such as inverted device structures of the bulk heterojunction geometry device, which allows for more stable metal electrodes, the choice of more photostable active materials, the introduction of interfacial layers, and roll-to-roll fabrication, which promises fast and cheap production methods while creating its own challenges in terms of stability.

Stability of polymer solar cells.

Preliminary data on the fabrication of 0.1 m 2 polymer solar cells are presented. The process employed screen-printing of an active layer onto an indium-tin-oxide (ITO) electrode pattern (50 Ω square −1 ) on a 200 μm polyethyleneterphthalate (PET) substrate. After the printing, vacuum coating of an optional layer of C 60 and the final aluminium electrode was employed to complete the device. The active layer consisted of poly-1,4-(2-methoxy-5-ethylhexyloxy)phenylenevinylene (MEH-PPV). Chlorobenzene was used as solvent for the screen-printing process. The design of the solar cell module was chosen to employ both serial and parallel connection of individual solar cells. Thirteen individual solar cells with an active area of 7.2 cm 2 were thus connected in series. The serial connection was chosen to reduce the current density for the large area employed. A step up in voltage is thus preferable to avoid resistive loss. The parallel connection of seven such rows through a screen-printed silver bus gave a solar cell module measuring 40 cm × 25 cm (0.1 m 2 ). The active area was 65% of the total area. The remaining 35% of the area was used for interconnections between cells and for the separation between rows. The 65% active area was chosen to encompass a good margin for prototyping/research and to keep contact resistances between the cells low. In a fully automated process the active area could perhaps reach 90–99% interval but problems with current extraction and interconnections were found to become very critical. There are obvious shortcomings to this approach but the advantage of low current density is believed to be the biggest problem in efficient energy extraction from the module when no simple method for reducing the sheet resistance is available. In the simple geometry ITO/MEH-PPV/aluminium the module gave an open circuit voltage ( V oc ) of 10.5 V, a short circuit current ( I sc ) of 5 μA, a fill factor (FF) of 13% and an efficiency ( η ) of 0.00001% under AM1.5 illumination with an incident light intensity of 1000 W m −2 . A geometry employing a sublimed layer of C 60 (ITO/MEH-PPV/C 60 /Al) improved V oc , I sc , FF and η to 3.6 V, 178 μA, 19% and 0.0002%, respectively. The lifetimes ( τ ½ ) of the devices defined as the time it takes for the module efficiency to attain half of its maximum value were found to improve significantly when a sublimed layer of C 60 was included between the polymer and the aluminium electrode. The modules were laminated with 200 μm polyethyleneterephthalate (PET) foil to mechanically protect the cells. τ ½ values of 150 h were typically obtained. This short lifetime is linked to reaction between the reactive metal electrode (aluminium) and the constituents of the active layer. The modules were tested outdoors in different weather condition (wind, high temperature excursion, rain, snow). Tested during a storm the polymer photovoltaic laminate was subject to vibration stress and deformation and delamination in the organic layer was observed with fast bleaching of the active material. Efficient encapsulation with barriers that has very low oxygen and water permeabilities will be needed before future commercialisation can be anticipated.

Large area plastic solar cell modules

Strategies for incorporation of polymer photovoltaics into garments and textiles

Optimizations of large area quasi-solid-state dye-sensitized solar cells

In this paper we present an attempt to substitute liquid electrolyte (LC) dye-sensitized solar cells (DSSCs) by quasi-solid-state constructions (SC) for semi-transparency application adopting organic/inorganic gels in combination with standard (Pt based) and alternative (PEDOT:PSS based) counter electrodes. Gel polymer electrolytes are prepared by incorporating a liquid electrolyte into a polymer matrix such as polymethyl-methacrylate (PMMA) using propylene carbonate (PC) as gelling solvent. SC employing gel electrolytes with a high content in PC have been shown to exhibit increased lifetime up to 70 h under A.M. 1.5 irradiation. Counter electrodes were prepared by an airbrushing and tape casting technique of Pt salt solutions or by spin coating of commercial PEDOT:PSS solution. PEDOT:PSS counter electrodes were found to show similar I 3 − /I − catalytic activities to Pt based counter electrodes and the best SC obtained gave a short circuit current of 2 mA cm −2 and a open circuit voltage of 625 mV.

Quasi-solid-state dye-sensitized solar cells: Pt and PEDOT:PSS counter electrodes applied to gel electrolyte assemblies

We report the synthesis of (E)-3-(4-bromo-2,5-dioctylphenyl)-2-(4-vinylphenyl)acrylonitrile (5). We further report the synthesis of conjugated polymer materials by palladium-catalyzed Heck coupling polymerization of 5 and 4-bromo-2,5-dioctyl-4‘-vinylstilbene (3) in the presence of 4‘-(4-bromophenyl)-2,2‘:6‘,2‘ ‘-terpyridine (8), giving poly(dioctylstilbenevinylene)s terminated by a terpyridine moiety. Their assembly using ruthenium complexation led to coordination homopolymers and copolymer with tetrafluoroborate counterions. The materials were characterized using SEC, MALDI, NMR, UV−vis, and fluorescence spectroscopy. The polymers were found to transfer energy to the complexes as seen through the complexes ability to quench fluorescence. The coordination polymers were applied to photovoltaics, and two types of devices were prepared:  polymer solar cells obtained by spin-coating of the coordination polymer solution onto PEDOT:PSS-covered ITO substrates and dye-sensitized solar cells obtained by absorption...

Matteo Biancardo

Papers

Large area plastic solar cell modules

Strategies for incorporation of polymer photovoltaics into garments and textiles

Optimizations of large area quasi-solid-state dye-sensitized solar cells

Quasi-solid-state dye-sensitized solar cells: Pt and PEDOT:PSS counter electrodes applied to gel electrolyte assemblies

Synthesis of Conjugated Polymers Containing Terpyridine−Ruthenium Complexes: Photovoltaic Applications