Alexander Konkin

Slightly hydrogenated TiO2 with enhanced photocatalytic performance

Hydrogenated TiO2 (H-TiO2) has triggered intense research interest in photocatalysis due to its substantially improved solar absorption and superior activity. However, the main factors that induce the enhanced photocatalytic performance of H-TiO2 are still under debate. In order to clarify this issue, the structural properties of H-TiO2, and their effects on photo-generated charges are comprehensively investigated in this study. H-TiO2 nanoparticles with different hydrogenation degrees are rapidly synthesized through H2 plasma treatment in several minutes; and their photocatalytic activities are evaluated by methylene blue (MB) degradation and CO2 reduction in aqueous and gaseous media, respectively. The slightly hydrogenated TiO2 (s-H-TiO2) nanoparticles with the original white color exhibit enhanced photoactivity compared with the pristine TiO2 (pristine-TiO2) nanoparticles especially for CO2 reduction; while the gray or black H-TiO2 nanoparticles with higher hydrogenation degrees (h-H-TiO2) display much worse catalytic performances. Further investigations reveal that the higher ratio of trapped holes (O− centers) and a lower recombination rate induced by the increase of surface defects might be the critical factors for the high activity of s-H-TiO2; in contrast, h-H-TiO2 nanoparticles possess high concentration of bulk defects, leading to a significantly decreased amount of O− centers and enhanced non-radiative recombination, which strongly inhibit their photoactivity. These results might provide new insights into the photoactivity of H-TiO2, and pave the way for further studies of other hydrogenated metal oxides for photocatalytic applications.

Characterization of potential donor acceptor pairs for polymer solar cells by ESR, optical, and electrochemical investigations

In this report new PPV-PPE copolymers DE 69, DE 11 were compared with the state of the art materials MDMO-PPV and poly(3-alkylthiophenes) (P3DDT, P3OT). The optical band gap energy of the two copolymers DE 69, DE11 is somewhat higher than that one of MDMO-PPV. The electrochemical band gap was found to be lower for DE 69, DE11 related to for MDMO-PPV. The absorption coefficient of the new PPV-PPE copolymers is higher than for MDMO-PPV but in the same order of magnitude. Films from composites of MDMO-PPV/PCBM and DE69 or DE11 with PCBM show a clear photoluminescence quenching effect. At 77 K two kinds of LESR signals were identified, one of polarons (P+.) and one of radical anions of fullerenes. The LESR results show strong differences in kinetics between the separation and recombination processes of photoexcited charge carriers. The relaxation rates of paramagnetic centers were estimated by microwave power saturation experiments. Photovoltaic devices were prepared under ambient conditions on flexible PET-ITO foils with MDMO-PPV/ PCBM (1:3 wt. %) with ηAM1.5 = 2.4% and DE 69/ PCBM (1:3 wt. %) with ηAM1.5 = 1.75% (A=0.25 cm2, Pin = 100 mW/cm2).

Structure and Lattice Location of Ge Implanted 4H-SiC

Pseudomorphic 4H-(Si1-xC1-y)Gex+y solid solutions were formed by ion implantation at 600°C and rapid thermal annealing at implanted Ge concentrations below 10%. At higher implantation doses followed by annealing 3C-SiC inclusion and SiGe precipitates are formed. Transmission electron microscopy investigations accompanied with “atomic location by channeling enhanced microanalysis” of the annealed samples revealed an increasing incorporation of Ge on Si lattice sites.