No abstract

Solar cells based on organic-inorganic perovskite semiconductor materials have recently made rapid improvements in performance, with the best cells performing at over 20% efficiency. With such rapid progress, questions such as cost and solar cell stability are becoming increasingly important to address if this new technology is to reach commercial deployment. The moisture sensitivity of commonly used organic-inorganic metal halide perovskites has especially raised concerns. Here, we demonstrate that the hygroscopic lithium salt commonly used as a dopant for the hole transport material in perovskite solar cells makes the top layer of the devices hydrophilic and causes the solar cells to rapidly degrade in the presence of moisture. By using novel, low cost, and hydrophobic hole transporters in conjunction with a doping method incorporating a preoxidized salt of the respective hole transporters, we are able to prepare efficient perovskite solar cells with greatly enhanced water resistance.

Recent development of metal-organic frameworks (MOFs) for CO 2 capture and CH 4 storage is reviewed. Strategies being used to improve CO 2 adsorption uptake at low pressures or CH 4 storage capacity of MOFs are highlighted, and the advantages and disadvantages of each strategy are discussed. Finally, some outlooks are presented for future research.

We report the design, synthesis, and characterization of a series of thieno [3,4-b]thiophene acceptor blocks with octyl (T8), phenyl (TP), perfluorooctyl (TF8), and perfluorophenyl (TFP) side groups. Their subsequent copolymerization with dithienylbenzodithiophene by direct arylation polymerization afforded novel low bandgap poly(thienothiophene-alt-dithienylbenzodithiophene) (PTB) polymers. The strongly electron withdrawing TF8 and TFP groups were shown to significantly lower both E HOMO and E LUMO levels and gave computed copolymer ground-to-excited state dipole changes (Δμ ge ) that were relatively higher than for the nonfluorinated analogues. These materials show favorably aligned energy levels relative to conventional fullerenetype acceptors, which should allow them to perform well in organic photovoltaics.

Efficient water splitting using light as the only energy input requires stable semiconductor electrodes with favorable energetics for the water-oxidation and proton-reduction reactions. Strategies to tune electrode potentials using molecular dipoles adsorbed to the semiconductor surface have been pursued for decades but are often based on weak interactions and quickly react to desorb the molecule under conditions relevant to sustained photoelectrolysis. Here, we show that covalent attachment of fluorinated, aromatic molecules to p-GaAs(1 0 0) surfaces can be employed to tune the photocurrent onset potentials of p-GaAs(1 0 0) photocathodes and reduce the external energy required for water splitting. Results indicate that initial photocurrent onset potentials can be shifted by nearly 150 mV in pH -0.5 electrolyte under 1 Sun (1000 W m ) illumination resulting from the covalently bound surface dipole. Though X-ray photoelectron spectroscopy analysis reveals that the covalent molecular dipole attachment is not robust under extended 50 h photoelectrolysis, the modified surface delays arsenic oxide formation that results in a p-GaAs(1 0 0) photoelectrode operating at a sustained photocurrent density of -20.5 mA cm within -0.5 V of the reversible hydrogen electrode.