High-Performance TiO₂ Photoanode with an Efficient Electron Transport Network for Dye-Sensitized Solar Cells

A titanium organic sol was synthesized for the modification of conventional porous TiO2 photoanodes for dye-sensitized solar cells (DSSCs). As a result, a compact thin TiO2 film was superimposed on the porous TiO2 structure as an efficient electron transport network, covering bare conducting substrate surface (FTO) and bridging gaps between TiO2 nanoparticles, which was confirmed by scanning electron microscope (SEM) and transmission electron microscope (TEM). Dark current measurement suggested that the sol modified photoanode had a remarkably slower recombination rate of the photoelectrons due to the reduced bare FTO surface in comparison with the porous photoanode. The network facilitates the electron transfer in the DSSC process by removing the dead ends of electron pathways, connecting gaps along the electron pathways, and physically enlarging electron pathways, which can be demonstrated by the performance improvement of photocurrent and open-circuit potential. Consequently, the overall energy conversion efficiency of the DSSC was significantly enhanced by 28% after this simple and low-cost organic sol modification. The significant performance improvements observed from the organic sol modified DSSCs suggest that the proposed modification method is a promising alternative to the traditional TiCl4 modification method

Solid-State Composite Electrolyte LiI/3-Hydroxypropionitrile/SiO₂ for Dye-Sensitized Solar Cells

A new compound, LiI(3-hydroxypropionitrile)2, is reported here. According to its single-crystal structure (C2/c), this compound has 3-D transporting paths for iodine. Further ab initio calculation shows that the activation energy for diffusion of iodine (0.73 eV) is much lower than that of lithium ion (8.39 eV) within the lattice. Such a mono-ion transport feature is favorable as solid electrolyte to replace conventional volatile organic liquid electrolytes used in dye-sensitized solar cells (DSSC). LiI and 3-hydroxypropionitrile (HPN) can form a series of solid electrolytes. The highest ambient conductivity is 1.4 × 10-3 S/cm achieved for LiI(HPN)4. However, it tends to form large crystallites and leads to poor filling and contact within porous TiO2 electrodes in DSSC. Such a drawback can be greatly improved by introducing micrometer-sized and nanosized SiO2 particles into the solid electrolyte. It is helpful not only in enhancing the conductivity but also in improving the interfacial contact greatly. Consequently, the light-to-electricity conversion efficiency of 5.4% of a DSSC using LiI(HPN)4/15 wt % nano-SiO2 was achieved under AM 1.5 simulated solar light illumination. Due to the low cost, easy fabrication, and relatively high conversion efficiency, the DSSC based on this new solid-state composite electrolyte is promising for practical applications

Solid-State Composite Electrolyte LiI/3-Hydroxypropionitrile/SiO₂ for Dye-Sensitized Solar Cells

A new compound, LiI(3-hydroxypropionitrile)2, is reported here. According to its single-crystal structure (C2/c), this compound has 3-D transporting paths for iodine. Further ab initio calculation shows that the activation energy for diffusion of iodine (0.73 eV) is much lower than that of lithium ion (8.39 eV) within the lattice. Such a mono-ion transport feature is favorable as solid electrolyte to replace conventional volatile organic liquid electrolytes used in dye-sensitized solar cells (DSSC). LiI and 3-hydroxypropionitrile (HPN) can form a series of solid electrolytes. The highest ambient conductivity is 1.4 × 10-3 S/cm achieved for LiI(HPN)4. However, it tends to form large crystallites and leads to poor filling and contact within porous TiO2 electrodes in DSSC. Such a drawback can be greatly improved by introducing micrometer-sized and nanosized SiO2 particles into the solid electrolyte. It is helpful not only in enhancing the conductivity but also in improving the interfacial contact greatly. Consequently, the light-to-electricity conversion efficiency of 5.4% of a DSSC using LiI(HPN)4/15 wt % nano-SiO2 was achieved under AM 1.5 simulated solar light illumination. Due to the low cost, easy fabrication, and relatively high conversion efficiency, the DSSC based on this new solid-state composite electrolyte is promising for practical applications

Property Influence of Polyanilines on Photovoltaic Behaviors of Dye-Sensitized Solar Cells

The influence of polyanilines (PANIs) as hole conductors on the photovoltaic behaviors of dye-sensitized solar cells is studied. The current−voltage (I−V) characteristics and the incident photon to current conversion efficiency (IPCE) curves of the devices are determined as the function of different conductivities and morphologies of PANIs. The results show that the conductivity of PANIs affects the performance of the devices greatly, and PANI with the intermediate conductivity value (3.5 S/cm) is optimum. In addition, the effects of both the film formation property and the cluster size of polyanilines on the photovoltaic behaviors of the devices are also discussed

Cheap and Environmentally Benign Electrochemical Energy Storage and Conversion Devices Based on AlI₃ Electrolytes

Cheap and environmentally benign electrochemical energy conversion and storage devices, including a dye-sensitized solar cell (DSSC) using an AlI3−ethanol electrolyte and a new Al/I2 primary battery, are reported. The AlI3−ethanol electrolyte can be prepared simply by adding aluminum powder and iodine into ethanol at ambient conditions. The DSSC using this AlI3−ethanol electrolyte achieved an energy conversion efficiency of 5.9% at AM 1.5 (100 mW/cm-2). In the Al/I2 battery, AlI3 is formed spontaneously when aluminum and iodine electrodes are brought into contact at room temperature. Then I- anions transport across the AlI3 solid electrolyte for further electrochemical reactions

Vertical Stratification and Interfacial Structure in P3HT:PCBM Organic Solar Cells

Structure and morphology play a critical role in determining the performance of organic photovoltaic devices. In this paper, variation of the postannealing cooling rate is used to create a series of “snapshots” of the vertical and interfacial reorganization processes that occur upon annealing. The data show that slower cooling rates result in significantly enhanced device efficiencies primarily driven by increased short circuit current and fill factor. UV−vis spectroscopy, X-ray diffraction (XRD), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), atomic force microscopy (AFM), and contact angle measurements are used to probe the origin of these improvements. Our results show evidence for a distinct and changing vertical stratification and interfacial structure in the device throughout the annealing process, with both composition and crystallinity varying through the active layer. The implications of these changes are discussed in terms of device properties

Influence of the Alkyl Substituents Spacing on the Solar Cell Performance of Benzodithiophene Semiconducting Polymers

Three semiconducting polymers containing benzodithiophene with decylphenylethynyl substituents have been synthesized for which the spacing between alkyl substituents has been systematically increased by introduction of thiophene and bithiophene units in the backbone of the polymer. As the spacing between the side chains increased, an increase of the weight ratio of polymer to fullerene acceptor was required for achieving the highest power conversion efficiency of bulk heterojunction solar cells. The spacing between the side chains of the polymers was estimated from DFT calculations. The TMAFM analysis of polymer PCBM blends showed that the smooth films exhibited the highest solar cell performance

Synthesis and Electronic Properties of Semiconducting Polymers Containing Benzodithiophene with Alkyl Phenylethynyl Substituents

Semiconducting polymers containing benzodithiophene with decyl phenylethynyl and hexadecyl phenylethynyl substituents have been synthesized by Stille coupling polymerization. The optoelectronic properties of the synthesized polymers have been investigated. The synthesized polymers were tested in bulk heterojunction solar cells