PEDOT temperature

The same group recently reported that the TBB defects can be brought below the nuclear magnetic resonance (NMR) detection limit by employing similar polymerization conditions (i-BuOK in THF at room temperature) in the synthesis of naphthyl-substituted PPVs 51-53 [112]. Although the absorption and PL spectra of all three polymers are similar, the EL can be finely tuned between 486 nm (for 52) and 542 nm (for 53). The external QE (studied for ITO/PEDOT/polymer/Ba/Al device) is also sensitive to the substituents pattern in the naphthyl pendant group 0.08% for 51, 0.02% for 52, and 0.54% for 53. 

Danielsson et al. [25] have studied the synthesis of PEDOT in ionic liquids that utilize bulky organic anions, l-butyl-3-methylimidazolium diethylene glycol monomethyl ether sulfate and l-butyl-3-methylimidazolium octyl sulfate, the latter of which is a solid at room temperature and thus requires the addition of either monomer or solvent (in this case water) to form a liquid at room temperature. Polymerization in a water-free ionic liquid was only possible in the octyl sulfate species, but the polymerization of EDOT was successful in aqueous solutions of both the ionic liquids (0.1 M). The ionic liquid anions appear to be mobile within the polymer, exchangeable with chloride ions at a polymer/KCl(aq) interface, but it is interesting that when the PEDOT is in aqueous solutions of the ionic liquid, at higher concentrations (0.01-0.1 M) the imidazolium cation can suppress this anion response. The ion mobility in both the ionic liquid and in the polymer film in contact with the solution is significantly increased by addition of water. 

In unoriented metallic conducting polymers like PANI-CSA, PPy-PFf, PEDOT-PF6, etc. [[Pg.111]

Fig. 5.10. Temperature dependent I/V characteristics of a p-type diode (ITO/ PEDOT/MDMO-PPV/LiF-Al), in which the different work functions of the electrodes guarantee ambipolar charge injection (electrons at the LiF-Al electrode, holes at the ITO/PEDOT electrode)...

Figure 5.11 summarizes the temperature dependent transport behavior of unipolar and ambipolar diodes based on MDMO-PPV. Below 190 K, the hole-controlled device (ITO/PEDOT and Au contact) and the ambipolar device (ITO/PEDOT and LiF-Al contact) behave identically. Trap-free SCLC transport is observed and the mobility at this temperature is estimated to be around 10-8 cm2/Vs. For the ambipolar device, a diode-like turn-on is... 

Fig. 5.12. Temperature dependent I/V characteristics of a bulk heterojunction device (ITO/PEDOT/MDMO-PPV PCBM/LiF-Al) in the dark (top) and under illumination (bottom)...

Figure 5.13 (top) displays the frequency spectra of the measured capacitance for temperatures ranging from 20 K to 300 K for a standard cell (ITO/PEDOT/MDMO-PPV PCBM/Al). The arrow indicates increasing temperatures. One clearly observes a step which is shifted to higher frequencies as the temperature increases. In order to evaluate the position of the steps, it is better to plot wdC/dw versus w, rather than C(u>) versus w. Figure 5.13 (bottom) shows the normalised deviated frequency spectrum of the capacitance. The steps now appear as maxima within the individual curves, and the corresponding critical frequency wq can be derived more ac-... 

In order to understand the performance of the tandem device, low temperature transport studies are a valuable tool. Diodes made from pristine MDMO-PPV and in composites with PTPTB are compared. ITO/PEDOT and Au electrodes are chosen to guarantee hole-only devices. This special choice of the electrodes is a successful technique for improving our understanding of transport failures. The proper choice of contacts allows us to produce p-type or n-type diodes from the same semiconductor, depending on the selectivity of the contact. For instance, Au is a hole-injection contact for most of the polymeric semiconductors, while Ca is an electron-injection... 

This view of Voc generation is additionally supported by the fact that the values of the temperature coefficient dUoc/dT = -(1.40-1.65) mVK-1 for the cells under the present study (with bilayer LiF/Al and ITO/PEDOT contacts) coincide with those for polymer/fullerene bulk heterojunction solar cells of the previous generation (with the same components of the active layer but without LiF and PEDOT contact layers) [156]. In this picture, the temperature dependence of Voc is directly correlated with the temperature dependence of the quasi-Fermi levels of the components of the active layer under illumination, i.e., of the polymer and the fullerene. Therefore, the temperature dependence of Voc over a wide range, and in particular V),c(0 K), are essential parameters for understanding bulk hetero junction solar cells. 

FIG. 3.21. J-V characteristics of the conducting organic polymer diode ITO/PEDOT PSS/MEH-PPV/Au on the log-log scale at different temperatures, where the thickness of MEH-PPV is 65 nm. The symbols represent the experimental data, while the solid lines are the calculated values using Eq. (3.42) at the corresponding temperatures [53],... 

FIG. 3.35. Experimental J—V characteristics of an ITO/PEDOT PSS/PCBM/Au injection limited electron current (triangles) and calculated space charge limited hole current in OC4C10-PPV (circles) for a thickness of L = 170 nm and temperature T = 290 K. The inserted figure represents die device band diagram under the flat band condition of a bulk heterojunction solar cell using Au as a top electrode [65]. 

Conducting polymers like commercially available PEDOT PSS are the third class of printable conductors. However, their conductivity (maximum 500 S/ cm for PEDOT PSS [11]) is several orders of magnitude lower than the conductivity of metals. The advantages of PEDOT PSS are its transparency, flexibility and low-temperature post-processing the thermal treatment is only necessary to remove residual solvent, no sintering is required. 

Under radiation damage-free eonditions, we show a clear indication for a surface reaction of P(VDF-TrFE) with A1 electrodes, not only for evaporated aluminium as top electrode, but also, at room temperature, for the aluminium as bottom electrode. In contrast, for PEDOT PSS, the XPS measiuements indicate a layer-by-layer structure of PEDOT PSS/P(VDF-TrFE) without any interface modification. This could be the reason for lower relaxation times, higher switching frequencies and, in consequence, a better field dependenee of the ferroelectric polarisation, if we choose PEDOT PSS as material for the electrode, especially for thin films of the eopolymer. 

DBEDOT (0.01-2 g) was incubated at 60 °C for 24 h and dried in vacuo (0.1 mbar) at room temperature to give black crystals of bromine-doped PEDOT. 

In this contribution, we discuss the impact that CuPc C6o absorber composition and its preparation temperature has on device PV parameters as well as on electrical and transport properties. ITO/3,4-polyethylene-dioxythiophene polystyrenesulfonate (PEDOT PSS)/CuPc C6o/Mg/Ag OSCs are investigated. 

ITO/PEDOT PSS/CuPc C6o/Mg/Ag organic solar cells were fabricated on ITO (5 Q/squarc sheet resistance)-coated glass substrates. After solvent cleaning, the ITO/glass substrates were spin-coated by a PEDOT PSS layer and immediately transferred into the deposition chamber. A 70 nm-thick CuPc C60 blend layer was prepared by organic vapour phase deposition (OVPD ) [2, 3], The Mg/Ag back contacts were deposited by thermal evaporation in high vacuum (p 10 7 mbar) on non-air-exposed absorber surfaces. The device preparation details can be found elsewhere [4], The compositional and substrate temperature (Tsubstrate) investigations are carried out on type A and B devices with nonoptimised and optimised contacts, respectively. 

Fig. 1. Efficiency of ITO/PEDOT PSS/CuPc C60/Mg/Ag OSCs as a function of CuPc C60 blend layer (a) composition and (b) preparation temperature.

Fig. 2. (a) Diode quality factor and (b) series resistance of the ITO/PEDOT PSS/ CuPc C60/ Mg/Ag OSCs as a function of preparation temperature. The doted lines are guides to the eye. 

The diode quality factor n of type A devices decreases as a function of substrate temperature in Figure 2a from 2.4-2.6 at Tsubstrate = 131°C or Tsubstrate = 187°C to 1.5 at Tsubstrate = 151°C. The behavior of the series resistance (Rs) with temperature is shown in Fig. 2b. The minimum Rs = 0.27 Q x cm2 is achieved for type B OSCs at Tsubstrate = 148°C. The enhancement of the devices PV and diode parameters with the temperature up to 150°C can be explained by (i) an improved separation of the CuPc and Cm donor and acceptor materials in an interpenetrated absorber network, (ii) enhanced crystalline perfection of the CuPc domains [4] and therefore improved transport properties, i.e., better collection efficiency of photogenerated carriers at the respective electrode. Alteration of the photoelectrical parameters at higher temperatures can be attributed to the potential degradation of the PEDOT buffer layer. 

For EL, the devices were driven under constant forward bias (Ca negative with respect to PEDOT PSS / ITO) and their emission was recorded using an Oriel InstaSpec IV spectrograph. The temperature was varied using a continuous-flow He cryostat (Oxford Instruments OptistatCF). For PL, the devices were optically excited through the ITO anode using a 407-nm pulsed diode laser (Pico-Quant LDH400). 

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