Huajun Shen

Charge-carrier dynamics in hybrid plasmonic organic solar cells with Ag nanoparticles

To understand the effects of Ag nanoparticles NPs on the performance of organic solar cells, we examined the properties of hybrid poly3-hexylthiophene:6,6-phenyl-C61-butyric-acid-methylester:Ag NP solar cells using photoinduced charge extraction with a linearly increasing voltage. We find that the addition of Ag NPs into the active layer significantly enhances carrier mobility but decreases the total extracted carrier. Atomic force microscopy shows that the Ag NPs tend to phase segregate from the organic material at high concentrations. This suggests that the enhanced mobility results from carriers traversing Ag NP subnetworks, and that the reduced carrier density results from increased recombination from carriers trapped on the Ag particles.

Plasmonic effects for light concentration in organic photovoltaic thin films induced by hexagonal periodic metallic nanospheres

We present a plasmonic nanostructure design by embedding a layer of hexagonal periodic metallic nanospheres between the active layer and transparent anode for bulk heterojunction organic solar cells. The hybrid structure shows broadband optical absorption enhancement from localized surface plasmon resonance with a weak dependence on polarization of incident light. We also theoretically study the optimization of the design to enhance the absorption up to 1.90 times for a typical hybrid active layer based on a low band gap material.

E-beam deposited Ag-nanoparticles plasmonic organic solar cell and its absorption enhancement analysis using FDTD-based cylindrical nano-particle optical model

We report the plasmon-assisted photocurrent enhancement in Ag-nanoparticles (Ag-NPs) embedded PEDOT:PSS/P3HT:PCBM organic solar cells, and systematically investigate the causes of the improved optical absorption based on a cylindrical Ag-NPs optical model which is simulated with a 3-Dimensional finite difference time domain (FDTD) method. The proposed cylindrical Ag-NPs optical model is able to explain the optical absorption enhancement by the localized surface plasmon resonance (LSPR) modes, and to provide a further understanding of Ag-NPs shape parameters which play an important role to determine the broadband absorption phenomena in plasmonic organic solar cells. A significant increase in the power conversion efficiency (PCE) of the plasmonic solar cell was experimentally observed and compared with that of the solar cells without Ag-NPs. Finally, our conclusion was made after briefly discussing the electrical effects of the fabricated plasmonic organic solar cells.

Thermal stability of Ni/Ti/Al ohmic contacts to p-type 4H-SiC

Low resistivity Ni/Ti/Al ohmic contacts on p-type 4H-SiC epilayer were developed, and their thermal stabilities were also experimentally investigated through high temperature storage at 600 °C for 100 h. The contact resistance of the Al/Ti/Ni/SiC contacts degraded in different degrees, and the contact morphology deteriorated with the increases of the average surface roughness and interface voids. X-ray spectra showed that Ni2Si and Ti3SiC2, which were formed during ohmic contact annealing and contributed to low contact resistivity, were stable under high temperature storage. The existence of the TiAl3 and NiAl3 intermetallic phases was helpful to prevent Al agglomeration on the interface and make the contacts thermally stable. Auger electron spectroscopy indicated that the incorporation of oxygen at the surface and interface led to the oxidation of Al or Ti resulting in increased contact resistance. Also, the formation of these oxides roughened the surface and interface. The temperature-dependence of the ...

Uneven splitting-ratio 1 \times 2 multimode interference splitters based on silicon wire waveguides

Two types of 1×2 multi-mode interference(MMI)splitters with splitting ratios of 85:15 and 72:28 are designed.On the basis of a numerical simulation,an optimal length of the MMI section is obtained.Subsequently,the devices are fabricated and tested.The footprints of the rectangular MMI regions are only 3×18.2 and 3×14.3(μm).The minimum excess losses are 1.4 and 1.1 dB.The results of the test on the splitting ratios are consistent with designed values.The devices can be applied in ultra-compact photonic integrated circuits to realize the“tap”function.

Efficiency Improved by Forming Gas Treatment for Si-Based Solar Cell Applications

The photovoltaic (PV) effects have been investigated and improved using efficient treatments both on single-crystalline (sc) and on multicrystalline (mc) silicon (Si) solar cells. The major effect of forming gas (FG) treatment on solar cell performance is the fill-factor values, which increase 3.75% and 8.28%, respectively, on sc-Si and mc-Si solar cells. As for the optimal 15%- ratio and 40-minute FG treatment, the conversion efficiency () values drastically increase to 14.89% and 14.31%, respectively, for sc- and mc-Si solar cells. Moreover, we can measure the internal quantum efficiency (IQE) values increase with -FG treatment under visible wavelength (400~900 nm) radiation. Thus based on the work in this research, we confirm that passivation has become crucial both in PV as well as in microelectronics fields. Moreover, the developed mc-Si solar cell by proper FG treatment is quite suitable for commercial applications.

Effect of Annealing on the Characteristics of Pd/Au Contacts to p-Type GaN/Al0.45Ga0.55N

The effect of annealing on the characteristics of Pd/Au contacts to p-type GaN/Al0.45Ga0.55N was investigated. The electrical characteristics of Pd/Au contacts and a p-GaN/AlGaN sample were measured after annealing at different temperatures from 550°C to 850°C. Changes in the surface electrical characteristic of p-GaN/AlGaN material were observed after each annealing step. It is indicated that the surface electrical characteristic of p-GaN/AlGaN material plays an important role in the current transport through Pd/Au pads. A possible reason for those changes is impurity contamination, most likely oxygen and carbon contamination introduced from processing. The microstructure of Pd on p-GaN/AlGaN was investigated by glancing-incidence x-ray diffraction (GXRD). The results of GXRD show that the AlPd2 and GaPd2 phases were formed at the interface after annealing, and the formation of these phases could be effective for forming ohmic contacts on p-GaN/AlGaN.

Plasmonic organic solar cell and its absorption enhancement analysis using cylindrical Ag nano-particle model based on finite difference time domain (FDTD)

We report the plasmon-assisted photocurrent enhancement in Ag nanoparticles (NPs)-embedded PEDOT:PSS/P3HT:PCBM organic solar cells, and theoretically investigate the causes of the improved optical absorption based on a cylindrical Ag-NPs model which is simulated with a finite difference time domain (FDTD) method. The proposed cylindrical Ag-NPs model is able to explain the optical absorption enhancement by the localized surface plasmon resonance (LSPR) modes, and to provide a further understanding of Ag-NPs shape parameters which play an important role to determine the broadband absorption phenomena in plasmonic organic solar cells.

Design and fabrication of a compact multimode interference splitter with silicon photonic nanowires

A compact multimode interference (MMI) splitter with silicon photonic nanowires on silicon-on-insulator (SOI) substrate is designed and fabricated. The footprint of the MMI section is only approximately 3×10 (\mu m). The simulation results show that the device may have a low excess loss of 0.04 dB. The transmission loss of the silicon photonics wire is measured to be 0.73±0.3 dB/mm. The compact size and low transmission loss allow the device to be used in ultra-compact photonic integrated circuits. The device exhibits a good light splitting function. In a spectral range of 1549-1560 nm, the excess loss is 1.5 dB and the average imbalance between the two channels is 0.51 dB.

Study on simultaneous formation of ohmic contacts on p- and n- type 4H-SiC using Ni/Ti/Al ternary system

In order to simplify the fabrication process of silicon carbide power MOSFETs (metal oxide semiconductor field effect transistors), the issue of the simultaneous formation process of ohmic contacts to both the p-well and n-source regions of the SiC devices using same contact materials and one step annealing needs to be addressed. In this study, Ni/Ti/Al ohmic contacts to p- and n-type 4H-SiC with different Ni thicknesses in different annealing conditions were fabricated and characterized, and the Ni (80 nm)/Ti (30 nm)/Al (80 nm) combination succeeded in forming low specific contact resistances (SCRs) of 4.2×10-5 Ω cm2 and 7.8×10-5 Ω cm2 for p- and n-type SiC, respectively, after annealing at 950 μC for 5 min.