PSS Formulation Research Articles

Flexible ITO-free polymer solar cells based on highly conductive PEDOT:PSS and a printed silver grid

We report efficient flexible polymer solar cells based on ITO and ITO-free semi-transparent electrodes consisting of either a highly conductive PEDOT:PSS formulation (PH1000) or a combination of printed silver grids and PH1000. As active layer material a polymer:fullerene bulk heterojunction based on PCDTBT:PC70BM (poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]:phenyl-C71-butyric acid methyl ester) was used. We demonstrate that the printed silver grid in combination with PH1000 leads to comparative device performances as ITO-coated PET substrates and has the potential for more.

Analysis of the degradation mechanism of ITO-free organic solar cells under UV radiation

This work reports on the stability of encapsulated ITO-free bulk heterojunction organic solar cells (BHJ-OSC) under UV radiation in ambient air with the layer sequence Cr/Al/Cr/photoactive layer (PAL)/poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate) (PEDOT:PSS)/metal-grid. The PAL consisted of poly(3-hexylthiophene) (P3HT) as a donor and (6,6)-phenyl-C60 butyric acid methyl ester (PCBM) as an acceptor. BHJ-OSC with this setup showed remarkable stability under continuous illumination (1000W/m2) with a low UV content. In contrast, the devices degraded significantly under UV radiation which was characterized by a reduction in fill factor and short-circuit current density. Additional experiments revealed an increase of the sheet resistance of the PEDOT:PSS layer which was interestingly much more pronounced in pure PEDOT:PSS samples as compared to samples where a PAL was deposited underneath. In addition, current extraction by linear increasing voltage (CELIV) measurements indicated a decrease of the effective charge carrier mobility of the PAL. Numerical simulations based on the experimentally determined parameters showed good agreement of the solar cell performance as a function of UV exposure duration. This suggests that the increase of the sheet resistance of the polymeric hole contact and to a lesser extent the change of the effective mobility of the PAL are the main factors governing the deterioration of the photovoltaic performance upon UV exposure. A comparison to devices with a setup ITO/ZnO/PAL/PEDOT:PSS and a full metallization showed clearly improved UV stability, although the absorption of UV in the PAL is very similar. This further supports our interpretation that the degradation of the PAL plays a very minor role. The issue with the degradation of the PEDOT:PSS can easily be solved by incorporating an UV-filter into the device or preferably the use of UV-stabilized PEDOT:PSS formulations.

A rational method for developing and testing stable flexible indium- and vacuum-free multilayer tandem polymer solar cells comprising up to twelve roll processed layers

We demonstrate a method for the preparation of multijunction polymer solar cells without the use of vacuum evaporation methods or indium tin oxide (ITO). The entire layer stack is prepared by printing or coating of each layer. The number of layers typically employed in complete devices exceeds ten and to efficiently identify layers and interfaces that are not robust we developed a double sided illumination method and demonstrate how layer thicknesses can be optimized with respect to the roll processing in the aim of achieving functional tandem devices. The devices were prepared directly on barrier foil and were later encapsulated. In this study the same active material comprising poly-3-hexylthiophene (P3HT) and phenyl-C61-butyric acid methyl ester ([60]PCBM) was employed using nanoparticle based zinc oxide for electron selectivity and several different PEDOT:PSS formulations for hole selectivity, electrode- and recombination layer formation. A novel slanted comb silver grid electrode structure was employed to enable efficient double sided illumination and minimize shunts. The operational stability of the tandem devices evaluated under ISOS-D-2 conditions demonstrated less variation in stability between devices than similar single junctions prepared in the same manner for reference. We demonstrate lifetime studies for 480h without any sign of degradation and estimate that the tandem or multijunction polymer solar cells are as stable as single junctions.

The Curious Out‐of‐Plane Conductivity of PEDOT:PSS

AbstractFor its application as transparent conductor in light‐emitting diodes and photovoltaic cells, both the in‐plane and out‐of‐plane conductivity of PEDOT:PSS are important. However, studies into the conductivity of PEDOT:PSS rarely address the out‐of‐plane conductivity and those that do, report widely varying results. Here a systematic study of the out‐of‐plane charge transport in thin films of PEDOT:PSS with varying PSS content is presented. To this end, the PEDOT:PSS is enclosed in small interconnects between metallic contacts. An unexpected, but strong dependence of the conductivity on interconnect diameter is observed for PEDOT:PSS formulations without high boiling solvent. The change in conductivity correlates with a diameter dependent change in PEDOT:PSS layer thickness. It is suggested that the order of magnitude variation in out‐of‐plane conductivity with only a 3‐4‐fold layer thickness variation can quantitatively be explained on basis of a percolating cluster model.

ZnO:Al-based recombination layers for polymer tandem solar cells: Influence of acidic or pH-neutral poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) formulations

We report on the fabrication of organic tandem solar cells which utilize sputtered ZnO:Al recombination layers in combination with the common p-type poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) polymer layer. The impact of the layer thickness on the device performance was investigated. Our experiments determined the minimal value of the ZnO:Al layer thickness in order to obtain a fully functional tandem solar cell. Although PEDOT:PSS is acidic and its application will reduce the initial ZnO:Al layer thickness by 10–50 nm, it could be applied to build functional tandem devices when the initial layer was thick enough to compensate for this loss in layer thickness. For comparison, we also investigated an alternative approach using a pH-neutral PEDOT:PSS formulation which lead to similar results regarding device performance. The conductivity and functionality of thicker ZnO:Al layers became sufficient to serve as a middle electrode to characterize the subcells within the tandem device. In this way, the bottom cell was measured after each subsequent top cell coating process step, revealing no alteration.

A step by step strategy for solution-processed quantum dots light emitting diodes

ABSTRACTSolution-based printing and coating processes have the potential to dramatically reduce the production costs of Organic Light Emitting Diodes. This is particularly true for Quantum Dots Light Emitting Diode (QDLEDs), the newborn in the field of LEDs, due to quantum dots price prohibiting wastage. Here, we report our latest results on the development of solutionprocessed QDLEDs. We have implemented a layer by layer strategy, from a whole evaporated small molecule based OLED to a hybrid QDLED developed by wet deposition techniques for the first layers and by evaporation for the last ones. Intermediate steps are discussed in this paper.First, we have worked on a poly(3,4-ethylenedioxythiophene poly(styrenesulfonate) (PEDOT:PSS) layer. The PEDOT:PSS formulation for inkjet printing and spin coating were optimised: wettability on an ITO substrate, jettability of the inkjet formulation and baking conditions were studied. Additives as surfactant and ethylene glycol were added to the commercial inkjet grade solution to improve the deposition process. As a consequence to this study, anisotropic conductivity of PEDOT:PSS was observed and is reported here. In particular, ethylene glycol demonstrated a strong ability to increase the parallel conductivity by several orders of magnitude, but not the vertical one.Then, inkjet-printed and spin-coated device performances are compared to complete this first study. Hybrid devices with an efficacy of 12cd/A at 4V were obtained, with 2.17 % of EQE, and a luminance of 4000 cd/m2 at 4V.Finally, we succeeded in the development of our first QDLED based on CdSe core/ CdSZnS shell quantum dots emitting at a wavelength of 600nm. Quantum dots were inkjet printed, in order to waste as little as possible this very expensive material.

Organic Semiconductors for Thermoelectric Applications

The thermoelectric performance of thin films fabricated from two commercially available, highly conductive polymer formulations based on poly (3,4-ethylendioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was investigated. In order to enhance the electrical conductivity, the high-boiling solvent dimethyl sulfoxide (DMSO) was added. By changing the content of DMSO the electrical conductivity was increased by a factor of two without changing the Seebeck coefficient or the thermal conductivity. We achieved ZT = 9.2 × 10−3 at room temperature upon the addition of 5 vol.% DMSO to the PEDOT:PSS formulation.

Polymeric anodes from poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) for 3.5% efficient organic solar cells

We present highly efficient indium tin oxide free polymer solar cells based on poly-(3-hexylthiophene-2,5-diyl) and C 61-bis-butric-acid-methyl-ester (P3HT:bisPCBM) comprising a polymeric anode from highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) formulations. The film conductivity was optimized by various additives. We found conductivities of almost 600 S/cm upon the addition of dimethylsulfoxide. The wetting properties of different PEDOT:PSS formulations were investigated by contact angle measurements. The optimized high conductivity in combination with the good film forming properties allow for the fabrication of highly efficient organic solar cells with an external power conversion efficiency of 3.5% with PEDOT:PSS as polymeric anode.

Plasma patterning of Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) anodes for efficient polymer solar cells

In this work we present indium tin oxide free polymer photovoltaic devices featuring a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) anode that has been patterned by oxygen plasma etching. By optimizing the PEDOT:PSS formulation and thickness, we achieved conductivities up to 400 S/cm. The best overall power conversion efficiency was found to be 2.2% under equivalent illumination to one sun with a PEDOT:PSS film conductivity of 300 S/cm.

Calculation of inelastic cross sections for H++Cs → H(n=2)+Cs+

The cross sections for the processes H++Cs → H(2p and 2s) +Cs+ were calculated in the center of mass energy range 250–2400 eV using a simple pseudopotential formalism for the potential curves and coupling matrix elements and a perturbed stationary state (pss) formulation for the calculation of the cross sections. The results are found to be in reasonable agreement with experiment.