Optimization of an Electron Transport Layer to Enhance the Power Conversion Efficiency of Flexible Inverted Organic Solar Cells

The photovoltaic (PV) performance of flexible inverted organic solar cells (IOSCs) with an active layer consisting of a blend of poly(3-hexylthiophene) and [6, 6]-phenyl C61-butlyric acid methyl ester was investigated by varying the thicknesses of ZnO seed layers and introducing ZnO nanorods (NRs). A ZnO seed layer or ZnO NRs grown on the seed layer were used as an electron transport layer and pathway to optimize PV performance. ZnO seed layers were deposited using spin coating at 3,000 rpm for 30 s onto indium tin oxide (ITO)-coated polyethersulphone (PES) substrates. The ZnO NRs were grown using an aqueous solution method at a low temperature (90°C). The optimized device with ZnO NRs exhibited a threefold increase in PV performance compared with that of a device consisting of a ZnO seed layer without ZnO NRs. Flexible IOSCs fabricated using ZnO NRs with improved PV performance may pave the way for the development of PV devices with larger interface areas for effective exciton dissociation and continuous carrier transport paths

Verfahren und Vorrichtung zur Herstellung von Deckelektroden auf organischen elektonischen Elementen

The invention relates to a process and an apparatus for producing covering electrodes on organic electronic elements. It is an object of the invention to provide possible ways of producing covering electrodes on organic electronic elements, by means of which these covering electrodes can be formed with a constant layer thickness and at a reproducible and increased coating rate while avoiding defects or influencing of organic layer components. According to the invention, semifinished parts for organic electronic elements without covering electrodes are arranged at a distance from at least two targets made of the covering electrode material in a vacuum chamber. The semifinished parts and the targets with in each case a magnetron sputtering source are moved relative to one another by means of a transport device. The magnetron sputtering sources with the targets are alternately supplied with an electric potential and a plasma by means of whose free charge carriers the covering electrodes are formed on the semifinished parts is generated between the targets

The effect of barrier performance on the lifetime of small-molecule organic solar cells

In this work, we use different encapsulations to protect vacuum-evaporated small molecule organic solar cells with a simple p-i-i-stack for lifetime studies. Our devices use ZnPc and C60 as active materials. Lifetimes (T50) in a range from 300 h for un-encapsulated devices to 4000 h for glass-encapsulated have been observed. We use a model to distinguish between the water vapor transmission rate (WVTR) of the barrier and an additional WVTR of the aluminum top electrode. For all observed devices a loss of 50% of initial efficiency is observed when 10 mg m−2 water entered the device. The losses are related to a reduction of short circuit current density only, whereas open circuit voltage and fill factor remains unaffected. We relate this to an interaction of the water molecules with C60. © 2011 Elsevier B.V

Slot-die processing and encapsulation of non-fullerene based ITO-free organic solar cells and modules

Organic photovoltaic (OPV) devices have shown remarkable performance progress in recent years, reaching current record power conversion efficiency (PCE) values of 16.4% for single junction and 17.3% for multi junction devices, owing mostly to the impressive developments made within synthesis of new non-fullerene acceptors. This progress places organic solar cells at the forefront of thin-film photovoltaic technology. However, in order to meet industrial demands and reach high performance values in industrial settings, further research and development efforts within roll-to-roll (R2R) and sheet-to-sheet (S2S) processing of OPV devices under ambient conditions are required. Furthermore, OPV modules being manufactured through such up-scaled processing techniques should ideally be developed from low cost materials, and show good stability towards various different operational stress conditions. In this work, we demonstrate combined R2R and S2S development of ITO-free OPV devices, which are based on the non-fullerene material system PBDB-T:ITIC. The devices are processed from R2R vacuum sputtering and S2S slot-die coating at ambient conditions, and reach cell PCE values of 5.5%. In addition, we introduce a correlation between different barrier films, both commercial and sputtered inorganic coatings on ultra-clean PET, and the lifetime of the developed devices. The results therefore demonstrate an important step in the development of OPV devices from R2R and S2S processes in industrial settings

Quantifying Performance of Permeation Barrier - Encapsulation Systems for Flexible and Glass-Based Electronics and their Application to Perovskite Solar Cells

Effective transparent barrier/encapsulation systems represent a key enabling technology for large‐area electronics. Securing stability to the environment is vital. Here, the effects of architectures, application processes, and water vapor transmission rates (WVTR) of transparent flexible ultra‐high permeation barrier films (UHPBF) applied to substrates with adhesive resins are unraveled for attaining long lifetime, and compared with polyethylene terephthalate and glass barriers. How strongly performance of barrier/adhesive systems depends on barrier orientation, adhesion, manipulation, defects, and storage procedures is quantified via calcium tests. Furthermore, it is found that introducing an additional adhesion‐promoting layer on the standard UHPBF stack reduces WVTRs by a factor of 5 compared to barriers without it. Finally, barriers are used for sealing and encapsulation of perovskite solar cells (PSCs) enabling the extraction of a relationship between WVTRs of barrier/adhesive systems and degradation rates (DR) of PSCs. DR fall exponentially when WVTRs decrease from 101 to 10−3 g m−2 d−1. Outside that range any gains or losses are mitigated by tailing of the sigmoid curve relating the two parameters. Results highlight important factors which will help those developing strategies relating to encapsulation, barrier, adhesive and sealant systems and stable optoelectronic devices on glass and flexible substrates

Roll-to-Roll Thin Film Coating on Fluoropolymer Webs - Status, Challenges and Applications

Fluoropolymer webs and membranes commonly exhibit superior optical properties such as high transmittance over a broad wavelength range and very good outdoor stability. Therefore, fluoropolymer films are used in architecture, for example, in membrane roofs and facades in stadiums, shopping malls, and airports or as front-side encapsulation for solar cells. However, thin film deposition on fluoropolymer webs both in vacuum and at atmospheric pressure face several critical challenges including poor mechanical and thermo-mechanical properties, especially low dimensional stability and low elastic modulus, high and textured surface roughness, and low adhesion of thin films. This paper discusses critical process parameters in roll-to-roll processing for both vacuum processes and wet coating processes with respect to the unique properties of fluoropolymer webs. Reactively sputtered oxide layers as well as wet coated ORMOCER (a trademark of the Fraunhofer Institute) layers were deposited on ethylene tetrafluoroethylene (ETFE), polyvinylidene difluoride (PVDF), and ethylene chlorotrifluoroethylene (ECTFE) webs form single and multilayer permeation barrier systems. Layer adhesion and permeation barrier performance was reviewed in relation to the relevant process parameters. Permeation barrier coatings were selected as lead application for this study. Barrier coatings are sensitive to substrate surface irregularities and mechanical damage due to low adhesion, high strain, or roll-to-roll processing issues and therefore were a good measure for the quality of the coating on the substrate. Reactively sputtered zinc-tin oxide (ZTO) layers as well as wet coated ORMOCER (R) layers showed surprisingly good adhesion on both ETFE and PVDF surfaces. Both ZTO and - with adhesion promotion treatment - aluminum oxide (Al2O3) layers have the potential for low water transmission rates (WVTR) below 5 x 10(-2) g/(m(2)d) at 38 degrees C/90 % RH. on these substrates. Further reduction of the WVTR using multilayer stacks was demonstrated with a combination of wet coated ORMOCER layers and sputtered ZTO layers yielding a WVTR of 1 x 10(-3) g/(m(2)d) at 38 degrees C/90 % RH. To achieve that, adapted process parameters and layer stack designs such as reduced web tension and lower layer thicknesses were needed. The potential of the coatings for specific outdoor application is discussed as well as possible ways to improve the polymer web itself to gain a larger process window for roll-to-roll coating on fluoropolymer webs. Demonstrating successful coating on ETFE and PVDF, the results reviewed in this paper potentially enable the use of coated fluoropolymer webs for functionalization of membrane roofs and facades with flexible thin film solar cells, thermal insulation and solar control functionality, flexible thin film electroluminescence, and organic light-emitting diode (OLED) lighting panels as well as electrochromic devices