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Artificial photosynthesis is an effective way of converting CO 2 into fuel and high value-added chemicals. However, the sluggish interfacial electron transfer and adsorption of CO 2 at the catalyst surface strongly hamper the activity and selectivity of CO 2 reduction. Here, we report a photocathode attaching zeolitic imidazolate framework-8 (ZIF-8) onto a ZnTe surface to mimic an aquatic leaf featuring stoma and chlorophyll for efficient photoelectrochemical conversion of CO 2 into CO. ZIF-8 possessing high CO 2 adsorption capacity and diffusivity has been selected to enrich CO 2 into nanocages and provide a large number of catalytic active sites. ZnTe with high light-absorption capacity serves as a light-absorbing layer. CO 2 molecules are collected in large nanocages of ZIF-8 and delivered to the ZnTe surface. As evidenced by scanning electrochemical microscopy, the interface can effectively boost interfacial electron transfer kinetics. The ZIF-8/ZnTe photocathode with unsaturated Zn-N x sites exhibits a high Faradaic efficiency for CO production of 92.9% and a large photocurrent of 6.67 mA·cm -2 at -2.48 V (vs Fc/Fc + ) in a nonaqueous electrolyte at AM 1.5G solar irradiation (100 mW·cm -2 ).

Two new donor-acceptor (D-A)-substituted S,N-heteroacene-based molecules were developed and investigated as hole-transporting material (HTM) for perovskite solar cells (PSCs). Optical and electrochemical characterization brought out that the energy levels of both HTMs are suitable for their use in PSCs. Consequently, a power-conversion efficiency of 17.7% and 16.1% was achieved from PSCs involving the HTM-1 and HTM-2, respectively. The optoelectronic properties in terms of series resistance, conductivity, and charge carrier recombination were further examined to unfold the potential of these new HTMs. Time-resolved photoluminescence spectroscopy brought out that the hole injection from the valence band of perovskite into HTMs follows the trend, which is in accordance with the position of the highest occupied molecular orbital. Overall, our findings underline the potential of S,N-heteroacene co-oligomers as promising HTM candidates for PSCs.

Blue and green dyes as well as NIR-absorbing dyes have attracted great interest because of their excellent ability of absorbing the incident photons in the red and near-infrared range region. A novel blue D-π-A dye (Dyenamo Blue), based on the diketopyrrolopyrrole (DPP)-core, has been designed and synthesized. Assembled with the cobalt bipyridine-based electrolytes, the device with Dyenamo Blue achieved a satisfying efficiency of 7.3% under one sun (AM1.5 G). The co-sensitization strategy was further applied on this blue organic dye together with a red D-π-A dye (D35). The successful co-sensitization outperformed a panchromatic light absorption and improved the photocurrent density; this in addition to the open-circuit potential result in an efficiency of 8.7%. The extended absorption of the sensitization and the slower recombination reaction between the blue dye and TiO 2 surface inhibited by the additional red sensitizer could be the two main reasons for the higher performance. In conclusion, from the results, the highly efficient cobalt-based DSSCs could be achieved with the co-sensitization between red and blue D-π-A organic dyes with a proper design, which showed us the possibility of applying this strategy for future high-performance solar cells.

We report on the optimization of the interfacial properties of titania in mesoscopic CH3NH3PbI3 solar cells. Modification of the mesoporous TiO2 film by TiCl4 treatment substantially reduced the surface traps, as is evident from the sharpness of the absorption edge with a significant reduction in Urbach energy (from 320 to 140 meV) determined from photothermal deflection spectroscopy, and led to an order of magnitude enhancement in the bulk electron mobility and corresponding decrease in the transport activation energy (from 170 to 90 meV) within a device. After optimization of the photoanode-perovskite interface using various sizes of TiO2 nanoparticles, the best photovoltaic efficiency of 16.3% was achieved with the mesoporous TiO2 composed of 36 nm sized nanoparticles. The improvement in device performance can be attributed to the enhanced charge collection efficiency that is driven by improved charge transport in the mesoporous TiO2 layer. Also, the decreased recombination at the TiO2-perovskite interface and better perovskite coverage play important roles.

A tailored optimization of perovskite solar cells requires a detailed understanding of the processes limiting the device efficiency. Here, we study the role of the hole transport layer (HTL) spiro-MeOTAD and its thickness in a mesoscopic TiO2-based solar cell architecture. We find that a sufficiently thick (200 nm) HTL not only increases the charge carrier collection efficiency but also the light harvesting efficiency. This is due to an enhanced reflection of a smooth HTL/Au-electrode interface. The rough CH3NH3PbI3 perovskite surface requires an HTL thickness of >400 nm to avoid surface recombination and guarantee a high open-circuit voltage. Analyses of the electroluminescence efficiency and the diode ideality factor show that the open-circuit voltage becomes completely limited by trap-assisted recombination in the perovskite for a thick HTL. Thus, spiro-MeOTAD is a very good HTL choice from the device physics' point of view. The fill factor analyzed by the Suns-Voc method is not transport limited, but trap-recombination limited as well. Consequently, a further optimization of the device has to focus on defects in the polycrystalline perovskite film.

Organolead iodide perovskite, CH3NH3PbI3, was prepared in the form of nanowire by means of a small quantity of aprotic solvent in two-step spin-coating procedure. One-dimensional nanowire perovskite with the mean diameter of 100 nm showed faster carrier separation in the presence of hole transporting layer and higher lateral conductivity than the three-dimensional nanocuboid crystal. Reduction in dimensionality resulted in the hypsochromic shift of both absorption and fluorescence spectra, indicative of more localized exciton states in nanowires. The best performing device employing nanowire CH3NH3PbI3 delivered photocurrent density of 19.12 mA/cm(2), voltage of 1.052 V, and fill factor of 0.721, leading to a power conversion efficiency (PCE) of 14.71% at standard AM 1.5G solar illumination. A small I-V hysteresis was observed, where a PCE at forward scan was measured to be 85% of the PCE at reverse scan.

A series of novel ionic liquids composed of imidazolium, pyridinium, pyrrolidinium, and ammonium cations with tricyanomethanide or tetracyanoborate anions were prepared. The ionic liquids were characterized by NMR and IR spectroscopy and ESI-mass spectrometry, and their physical properties were investigated. Solid state structures of the N-propyl-N-methylpyrrolidinium and triethylpropylammonium tetracyanoborate salts were obtained by single crystal X-ray diffraction. The salts that are liquid at room temperature were evaluated as electrolyte additives in dye-sensitized solar cells, giving rise to efficiencies 7.35 and 7.85% under 100 and 10% Sun, respectively, in combination with the standard Z907 dye.