Organometallic halide perovskite solar cells (PSCs) are extremely promising novel materials for thin-film photovoltaics, exhibiting efficiencies over 22% on glass and over 17% on foil 1, 2 . First, a sheet-to-sheet (S2S) production of PSCs and modules on 152x152 mm2 substrates was established, using a combination of sputtering, e-beam evaporation, slot die coating and thermal evaporation (average PCE of 14.6 ± 1.3 % over 64 devices, more than 10% initial PCE on modules). Later the steps towards a roll-to-roll production will be investigated, starting from the optimization of the stack to make it compatible with a faster production at low temperature. A water based SnOx nanoparticles dispersion was used as solution processable ETL, and the deposition process was scaled-up from spin coating to R2R slot die coating on a 300 mm wide roll of PET/ITO. R2R production is often carried out in ambient atmosphere and involve the use of large volumes of materials, thus a first point is the development of a green solvent and precursor system for the perovskite layer to prevent the emission of toxic compound in the environment. The first results on device fabrication are encouraging, which allow partial R2R manufacturing of flexible PSC (R2R coating of SnOx and perovskite, S2S for Spiro-OMeTAD and gold) with stabilized PCE of 12.6%, a remarkable value for these novel devices. This result can be considered an important milestone towards the production of efficient, low cost, lightweight, flexible PSC on large area.
The authors present experimental results on mechanically stacked organic solar modules and their advantage over standard tandem architectures. A four-terminal configuration of two single junction modules with complementary absorbing active layers uses the more efficient energy conversion of a tandem structure without the necessity of matching currents or voltages of electrically connected subcells. The presented combination of semitransparent and opaque solar cells consists of solution processed polymer-fullerene blends as active materials. A cost-effective mechanical scribing process is applied for the patterning of the deposited layers. The best devices have an efficiency of over 6.5% on an aperture area of 16 cm2 which equals a gain of 30% over the best single junction module fabricated by the same process. Optical simulations demonstrate a 32% increased annual energy output of a mechanically stacked device in comparison to a monolithic tandem structure using an equivalent geometry.
Screen-printing is studied as deposition technique for conjugated material based layers. For light emitting diode applications poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) is applied. For this material, batches with different molecular weight and different solution concentrations are subjected to rheology measurements. Also the influence of several printing parameters like squeegee speed and pressure, snap-off distance and mesh size of the screen on the film formation and final thickness is investigated. It is shown that for each material batch and solution concentration specific printer settings have to be used to obtain active layers that are suitable for opto-electronic applications.
Photovoltaics based on the principle of bulk donor-acceptor heterojunction are also tested using a blend of MEH-PPV mixed with the C60-derivative (6,6)-phenyl C61-butyric acid methyl ester (PCBM). Promising results have been obtained showing that screen-printing can be a suitable technique for the deposition of the active layer of polymer solar cells.
A new precursor route towards conjugated polymers is presented. Whereas difficulties occurred for the preparation of poly(2,5-thienylene vinylene) (PTV) derivatives via the existing precursor routes, PTV has been synthesised via a new developed "dithiocarbamate route" in good yields and satisfactory molecular weight. Structural characterisations of the conjugated polymers reveal an optical band gap around 1.7 eV. Organic field effect transistors and organic based photovoltaic devices were made and the results are discussed. Solar cells were produced using a blend of the precursor polymer and PCBM at various ratios. The conversion of the precursor polymer towards the conjugated polymer was performed in situ in film spin-coated from the blend. Promising energy conversion efficiencies were observed which were still improved by thermal annealing of the device at 70°C.