Fossil fuel alternatives, such as solar energy, are moving to the forefront in a variety of research fields. Polymer-based organic photovoltaic systems hold the promise for a cost-effective, lightweight solar energy conversion platform, which could benefit from simple solution processing of the active layer. The function of such excitonic solar cells is based on photoinduced electron transfer from a donor to an acceptor. Fullerenes have become the ubiquitous acceptors because of their high electron affinity and ability to transport charge effectively. The most effective solar cells have been made from bicontinuous polymer–fullerene composites, or so-called bulk heterojunctions. The best solar cells currently achieve an efficiency of about 5 %, thus significant advances in the fundamental understanding of the complex interplay between the active layer morphology and electronic properties are required if this technology is to find viable application.

Polymer–Fullerene Composite Solar Cells

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as stand-alone electrodes for organic solar cells have been optimized using a solvent post-treatment method. The treated PEDOT:PSS films show enhanced conductivities up to 1418 S cm−1, accompanied by structural and chemical changes. The effect of the solvent treatment on PEDOT:PSS has been investigated in detail and is shown to cause a reduction of insulating PSS in the conductive polymer layer. Using these optimized electrodes, ITO-free, small molecule organic solar cells with a zinc phthalocyanine (ZnPc):fullerene C60 bulk heterojunction have been produced on glass and PET substrates. The system was further improved by pre-heating the PEDOT:PSS electrodes, which enhanced the power conversion efficiency to the values obtained for solar cells on ITO electrodes. The results show that optimized PEDOT:PSS with solvent and thermal post-treatment can be a very promising electrode material for highly efficient flexible ITO-free organic solar cells.

Highly Conductive PEDOT:PSS Electrode with Optimized Solvent and Thermal Post-Treatment for ITO-Free Organic Solar Cells

The conductivity of PEDOT:PSS films was significantly enhanced from 0.3 S cm(-1) to 3065 S cm(-1) through a treatment with dilute sulfuric acids. PEDOT:PSS films with a sheet resistance of 39 Ω sq(-1) and transparency of around 80% at 550 nm are obtained. These PEDOT:PSS films with conductivity and transparency comparable to ITO can replace ITO as the transparent electrode of optoelectronic devices.

Solution‐Processed Metallic Conducting Polymer Films as Transparent Electrode of Optoelectronic Devices

A polymer composition includes a conductive polymer and at least one stretchability and electrical conductivity (STEC) enhancer, wherein a content of the STEC enhancer in the composition is at least about 1 wt.% of the composition.

Highly stretchable, transparent, and conductive polymer

Despite the relatively low efﬁciencyin comparison with conventional inorganic solar cells, thepotential of roll-to-roll processing and large-area processa-bility on ﬂexible low-cost substrates renders conjugatedpolymer-based organic solar cells (OSCs) very attractive asa cost-effective solution to the problem of energy shortage.Among the available BHJ systems, poly(3-hexylthiophene)(P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C

Efficient and Flexible ITO‐Free Organic Solar Cells Using Highly Conductive Polymer Anodes

The conductivity of a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film can be enhanced by more than two orders of magnitude by adding a compound with two or more polar groups, such as ethylene glycol, meso-erythritol (1,2,3,4-tetrahydroxybutane), or 2-nitroenthanol, to an aqueous solution of PEDOT:PSS. The mechanism for this conductivity enhancement is studied, and a new mechanism proposed. Raman spectroscopy indicates an effect of the liquid additive on the chemical structure of the PEDOT chains, which suggests a conformational change of PEDOT chains in the film. Both coil and linear conformations or an expanded-coil conformation of the PEDOT chains may be present in the untreated PEDOT:PSS film, and the linear or expanded-coil conformations may become dominant in the treated PEDOT:PSS film. This conformational change results in the enhancement of charge-carrier mobility in the film and leads to an enhanced conductivity. The high-conductivity PEDOT:PSS film is ideal as an electrode for polymer optoelectronic devices. Polymer light-emitting diodes and photovoltaic cells fabricated using such high-conductivity PEDOT:PSS films as the anode exhibit a high performance, close to that obtained using indium tin oxide as the anode.

High-Conductivity Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) Film and Its Application in Polymer Optoelectronic Devices†

The influence of anode buffer layers on the performance of polymer photovoltaic devices based on blends of poly3-hexylthiophene and 6,6-phenyl-C-61-buytyric acid methyl ester has been investigated. The buffer layers consist of poly3,4-ethylenedioxythiophene:polystyrenesulfonate PEDOT-PSS doped with different concentrations of mannitol. Improved power conversion efficiency, up to 5.2%, has been observed by reducing the resistance of PEDOT:PSS after doping. One extrapolation method has been developed to exclude the resistance from the connection of the electrodes from the total device resistance. The results confirm that the device improvement is due to the reduction of series resistance of the PEDOT:PSS after the mannitol doping. © 2007 American Institute of Physics. DOI: 10.1063/1.2437703 Organic photovoltaic devices PVs have attracted considerable attention due to their potential for flexible, lightweight, and low-cost applications of solar energy conversion. Recently, the power conversion efficiency PCE of photovoltaic cells around 5% has been realized. 1,2 In addition, through the optimization of the donor/acceptor energy levels, the efficiency up to 10% is expected from recent simulation

https://ir.nctu.edu.tw:443/bitstream/11536/11140/1/000244162300101.pdf

Modified buffer layers for polymer photovoltaic devices

The conductivity of poly(3,4‐ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) film can be enhanced by more than two orders in magnitude by adding a compound with two or more polar groups, such as ethylene glycol (EG), meso‐erythritol (IUPAC name: 1,2,3,4‐tetrahydroxybutane), or 2‐nitroethanol, into the PEDOT:PSS aqueous solution. The mechanism of the increase in conductivity for PEDOT:PSS has been studied using Raman spectroscopy and atomic force microscope (AFM). Here we propose that the change in conductivity is due to the conformational change of PEDOT chains in the film. In untreated PEDOT:PSS films, coil, linear, or expanded‐coil conformations of the PEDOT chains may be present. In treated PEDOT:PSS films, the linear or expanded‐coil conformations may becomes the dominant form for PEDOT chains. This conformational change results in the enhancement of charge‐carrier mobility in the film and leads to enhanced conductivity. The high‐conductivity PEDOT:PSS film is ideal as the electrode ...

/pdf/polymer-optoelectronic-devices-with-high-conductivity-poly-3-1mtdx9izrb.pdf

Chi Wei Chu

Papers

High-Conductivity Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) Film and Its Application in Polymer Optoelectronic Devices†

Modified buffer layers for polymer photovoltaic devices

Polymer Optoelectronic Devices with High-Conductivity Poly(3,4-Ethylenedioxythiophene) Anodes