Over 30% efficiency bifacial 4-terminal perovskite-heterojunction silicon tandem solar cells with spectral albedo.

We developed and designed a bifacial four-terminal perovskite (PVK)/crystalline silicon (c-Si) heterojunction (HJ) tandem solar cell configuration albedo reflection in which the c-Si HJ bottom sub-cell absorbs the solar spectrum from both the front and rear sides (reflected light from the background such as green grass, white sand, red brick, roofing shingle, snow, etc.). Using the albedo reflection and the subsequent short-circuit current density, the conversion efficiency of the PVK-filtered c-Si HJ bottom sub-cell was improved regardless of the PVK top sub-cell properties. This approach achieved a conversion efficiency exceeding 30%, which is higher than those of both the top and bottom sub-cells. Notably, this efficiency is also greater than the Schockley-Quiesser limit of the c-Si solar cell (approximately 29.43%). The proposed approach has the potential to lower industrial solar cell production costs in the near future.

Improving Memory Characteristics of Hydrogenated Nanocrystalline Silicon Germanium Nonvolatile Memory Devices by Controlling Germanium Contents.

Nonvolatile memory (NVM) with silicon dioxide/silicon nitride/silicon oxynitride (ONO(n)) charge trap structure is a promising flash memory technology duo that will fulfill process compatibility for system-on-panel displays, down-scaling cell size and low operation voltage. In this research, charge trap flash devices were fabricated with ONO(n) stack gate insulators and an active layer using hydrogenated nanocrystalline silicon germanium (nc-SiGe:H) films at a low temperature. In this study, the effect of the interface trap density on the performance of devices, including memory window and retention, was investigated. The electrical characteristics of NVM devices were studied controlling Ge content from 0% to 28% in the nc-SiGe:H channel layer. The optimal Ge content in the channel layer was found to be around 16%. For nc-SiGe:H NVM with 16% Ge content, the memory window was 3.13 V and the retention data exceeded 77% after 10 years under the programming condition of 15 V for 1 msec. This showed that the memory window increased by 42% and the retention increased by 12% compared to the nc-Si:H NVM that does not contain Ge. However, when the Ge content was more than 16%, the memory window and retention property decreased. Finally, this research showed that the Ge content has an effect on the interface trap density and this enabled us to determine the optimal Ge content.

Fabrication of ZnO nanorods for gas sensing applications using hydrothermal method.

We showed well-aligned zinc oxide (ZnO) nanorod arrays synthesized using hydrothermal method at atmospheric pressure. The influence of fabrication conditions such as Zn2+/hexamethylentriamin concentration ratio, and growth temperature on the formation of ZnO nanorods was investigated. Scanning Electron Microscope (SEM) images and X-ray Diffraction (XRD) analysis were used to confirm the single crystal of ZnO nanorods, which showed wurtzite structure with growth direction of [0001] (the c-axis). Photoluminescence (PL) measurements of ZnO nanorods revealed an intense ultraviolet peak at 388.5 nm (3.19 eV) at room temperature. The results showed that the ZnO seed layers had strong influence on the growth of vertically aligned ZnO nanorods. The gas sensor based on ZnO nanorod arrays had the most selectivity with n-butanol gas (within 2 surveyed gas: ethanol and n-butanol) and showed a higher sensitivity of 222, fast response time of 15 seconds, recovery time of 110 seconds and lower operating temperature of 200-250 °C than the sensor based on the ZnO film in the same detecting conditions.