Performance Enhancement in Powder-Fabricated Cu2(ZnSn)Se4 Solar Cell by Roll Compression.

Despite the improved conversion efficiency of Cu2(ZnSn)Se4 (CZTSe) solar cells, their roll-to-roll fabrication nonetheless leads to low performance. The selenization time and temperature are typically considered major parameters for a powder-based CZTSe film; meanwhile, the importance of the densification during the roll-to-roll process is often overlooked. The densification process is related to the porosity of the light-absorbing layer, where high porosity lowers cell performance. In this study, we fabricated a dense CZTSe absorber layer as a method of controlling the compression of a powder precursor (Cu1.7(Zn1.2Sn1.0)S4.0 (CZTS)) during the roll-press process. The increased particle packing density of the CZTS layer was crucial in sintering the powder layer into a dense film and preventing severe selenization of the Mo back electrode. The pressed absorber layer of the CZTSe solar cell exhibited a more uniform chemical composition determined using dynamic secondary ion mass spectrometry (SIMS). Under the AM 1.5G illumination condition, the power conversion efficiency of the pressed solar cell was 6.82%, while the unpressed one was 4.90%.

Centrifugal microfluidic device for the high-throughput synthesis of Pd@AuPt core-shell nanoparticles to evaluate the performance of hydrogen peroxide generation.

We propose a novel high-throughput screening platform using a centrifugal microfluidic device for producing combinatorial tri-metallic catalysts. The centrifugal device was designed to perform 60 reactions under different conditions on a single device. As a model to search for an optimal tri-metallic catalyst, we synthesized a variety of Pd@AuPt nanoparticles (NPs), in which Pd nanocubes served as a core, and Au and Pt atoms formed a shell. The centrifugal microfluidic device was etched on the top and bottom sides, in which two zigzag-shaped microchannels were patterned on the top side, and 60 reaction chambers were fabricated on the bottom side. Through the sophisticated zigzag-shaped microchannels, Pt2+ ion and Pd nanocube solutions were injected into the channel in one shot, and the centrifugal force equally and automatically divided the injected solutions into 60 aliquots during the rotation. By controlling the sophisticated channel dimensions and designing the passive valve structure, the Pt2+ ion, Pd nanocube, and Au3+ solutions were loaded into the reaction chamber in sequential order depending on the programmed rotational direction and speed. Therefore, the ratio of Au to Pt to synthesize Pd@AuPt core-shell NPs was changed from 0.028 : 1 to 12 : 1, and accordingly, the resultant 60 types of Pd@AuPt catalysts presented with different ratios of metal atom compositions. Then, we screened the catalytic activity of the Pd@AuPt NPs for generating H2O2 according to the degree of coating of Au and Pt, and the Pd@AuPt catalyst with the Au/Pt ratio at 0.5 turned out to be the most effective.

Strategies for the modification of adhesion at graphene/Al Interfaces: a first principles study.

Possibility of improving the adhesion at graphene/Al interfaces has been investigated by predicting interactions between monolayer graphene and Al (111) plane using first principles simulations. For the property modifications, either Ni atoms were adsorbed on one side of the graphene or the graphene is substitutionally doped with B. It was predicted that the adatoms or dopants modify local electronic or orbital structure, which subsequently promotes the bonding between the graphene and Al at local level thereby improving the bond strength at the interface. While improvement of interfacial properties was expected with the surface modification by a foreign element adsorption or substitutional doping of the graphene, low-concentration substitutional doping was predicted to be more effective in achieving improved adhesive properties of the graphene/Al nanointerface.