41 Whiskers are very thin, 0 -0.3 wm, single-crystalline ceramic "fibers" with the highest known tensile strengths.have low efficiencies of energy conversion due to poor photoinduced charge separation and transport of photogenerated charges."] When the light is absorbed in these polymers, electron-hole pairs are created in the form of excitons. The characteristic length of the exciton distribution is given by the inverse absorption coefficient, and can be on the order of 20-1000 nm. These excitons must then be dissociated, and the different photogenerated charges must be transported to electrodes to produce an appreciable photocurrent. Because the life cycle of the exciton includes both radiative and non-radiative decay, which give a lifetime in the range of nanoseconds, and the diffusion length of the exciton in these polymers is in the range of 10 nm, it is necessary to move the excited state to a site for charge dissociation within this distance and time. The dissociation often occurs in the strong electric field in the depletion layer that is created at the polymer/metal interface by the difference of electron affinities or ionization potentials of these materials. Only a small fraction of the photogenerated pairs will be able to transit this region, and thus contribute to the photocurrent.In order to improve the exciton dissociation it is necessary to distribute the sites for photoseparation. This approach involves the formation of a composite of two phaseseparated materials with different electron affinities, where one is the donor and the other is the acceptor material, making what is called a "bulk D-A heterojunction material",[2-61 which provides the spatially distributed interface necessary to dissociate the excitons. The free charges created at these D-A heterojunctions are then transported separately by donor or acceptor material, and are collected at the contacting electrodes. The two contacting electrodes are chosen so as to create a built-in electric field in the device, due to the different work functions of the electrodes, and in this way to enhance the photoseparation and the discharge of photoinduced carriers. Conjugated polymer/ buckminsterfullerene (C,,) composites, as well as two different polymers with different electron affinities, have been proposed for use as the D-A materials.[241We have focused on the use of polythiophenes in combination with C6,; earlier studies have reported on this system."] Several reasons can be given for this choice. First, the solubility and/or fusibility of these polymers allows formation of thin films of optical quality; they also allow formation of complex morphologies due to phase separation and supramolecular organization.17] Second, it is easy to tailor their optical properties by modifying the polythiophenes via simple substitution on the main chain, at least for bandgaps varying from 1.7 to 3 eV.I8] The lowest bandgap allows the creation of polymer light-emitting diodes in the near infrared rangeLy1 and matches well with the ultimate requirement for sola...

Spectroelectrochemical techniques have been used to study doping-induced reactions in conjugated polymers. Here, we report results on reduction reactions (n-doping) of the conjugated ladder polymer polybenzimidazobenzophenanthroline (BBL). The spectra are recorded in situ during applied potential in a three-electrode spectroelectrochemical cell. The spectral and thus the structural changes during the reduction (n-doping) of the polymer film at different electrode potentials are discussed. In contrast to most of the other conjugated polymers, this polymer shows four reversible redox reactions during n-doping, corresponding to various insulating and conducting forms of BBL.

No abstract

No abstract

No abstract

No abstract

All-solid-state photoelectrochemical cells have been constructed using films of a conducting polymer, poly(3-octylthiophene), and a polymer electrolyte, amorphous polyethylene oxide, complexed with the 1/U redox couple. An open-circuit voltage of 250 mV and a short-circuit current of 0.04 M/cm2 were obtained with white light illumination at approximately one sun. During illumination, a cathodic photocurrent was observed, indicating that the neutral poly(3-octylthiophene) behaves as a p-type semiconductor. From the spectral response, the junction responsible for the photocurrent generation is between the conducting polymer and the solid polymer electrolyte. The open-circuit voltage and short-circuit current dependence on intensity and variation of open-circuit voltage with redox couple concentration have also been studied. InfroductionThe electrical properties of conducting polymers are similar to those of conventional inorganic semiconductors, but they are generally less expensive and can be deposited onto large areas by various techniques such as sublimation, spin-coating, and solvent casting. In particular, electrically conducting polymers are interesting for use in potentially low-cost solar energy conversion, and in the early 1980s, they were studied for this application.

Outstanding improvement in power conversion efficiency (PCE) over 25% in a very short period and promising research developments to reach the theoretical PCE limit of single junction solar cells, 33%, enables organic–inorganic perovskite solar cells (OIPSCs) to gain much attention in the scientific and industrial community. The simplicity of production of OIPSCs from precursor solution either on rigid or flexible substrates makes them even more attractive for low-cost roll-to-roll production processes. Though OIPSCs show as such higher PCE with simple solution processing methods, there are still unresolved issues, while attempts are made to commercialize these solar cells. Among the major problems is the instability of the photoactive layer of OIPSCs at the interface of the charge transport layers and /or electrodes during prolonged exposure to moisture, heat and radiation. To achieve matched PCE and stability, several techniques such as molecular and interfacial engineering of components in OIPSCs have been applied. Moreover, in recent times, engineering on additives, solvents, surface passivation, and structural tuning have been developed to reduce defects and large grain boundaries from the surface and/or interface of organic–inorganic perovskite films. Under this review, we have shown recently developed additives and passivation strategies, which are strongly focused to enhance PCE and long-term stability simultaneously.