Significant increase of the photoresponse range and conductivity for a chalcogenide semiconductor by viologen coating through charge transfer.

Widening the photoresponse range while enhancing the electrical properties of semiconductors could reduce the complexity and cost of photodetectors or increase the power conversion efficiency of solar cells. Surface doping through charge transfer with organic species is one of the most effective and widely used approaches to achieve this aim. It usually features easier preparation over other doping methods but is still limited by the low physicochemical stability and high cost of the used organic species or low improvement of electrical properties. This work shows unprecedented surface doping of semiconductors with highly stable, easily obtained, and strong electron-accepting viologen components, realizing the significant improvement of both the photoresponse range and conductivity. Coating the chalcogenide semiconductor KGaS2 with dimethyl viologen dichloride (MV) yields a charge-transfer complex (CTC) on the surface, which broadens the photoresponse range by nearly 300 nm and improves the conductivity by 5 orders of magnitude. The latter value surpasses all records obtained by surface doping through charge transfer with organic species.

Coordination polymerization of nitrogen-rich linkers and dicyanamide anions toward energetic coordination polymers with low sensitivities.

The design and synthesis of energetic materials (EMs) with high energy and reliable stabilities has attracted much attention in the field of EMs. In this work, we employed a strategy of the coordination polymerization of mild dicyanamide ions (DCA-), two isomeric ligands 1-methyl-5-aminotetrazole (1-MAT) and 2-methyl-5-aminotetrazole (2-MAT) to construct energetic coordination polymers (ECPs). Four new ECPs {[Co(DCA)2(1-MAT)2]·H2O}n1, [Cu(DCA)2(1-MAT)]n2, [Cd(DCA)2(1-MAT)2]n3 and [Cd(DCA)2(2-MAT)2]n4 were successfully synthesized through solvent evaporation routes. Compounds 1 and 4 display 1D chains, while 2 and 3 exhibit 2D-layered structures. Compounds 1-3 with the 1-MAT ligand all exhibit reliable thermal stabilities (> 200 °C). The calculated heats of detonation (ΔHdet) of 1-3 are all higher than 1.4 kJ g-1, which are higher than traditional explosive TNT (1.22 kJ g-1) and the reported ECP AgMtta (HMtta = 5-methyl-1H-tetrazole, ΔHdet = 1.32 kJ g-1). Furthermore, sensitivity testing demonstrates that 1-4 features low mechanical sensitivity to external mechanical action in contrast with the extremely sensitive azide-based ECPs [Cu3(2-MAT)2(N3)6]n. In addition, compound 2 shows hypergolic properties via an 'oxidizer-fuel' drop experiment, demonstrating its application prospects in the field of propellants. This work details an approach of synthesizing multipurpose ECPs with reliable stabilities by introducing mild dicyanamide anions into nitrogen-rich skeletons.