Emission Mechanism of "Green Fuzzies" in High-mass Star Forming Regions

The Infrared Array Camera (IRAC) on the Spitzer Space Telescope has revealed that a number of high-mass protostars are associated with extended mid-infrared emission, particularly prominent at 4.5-micron. These are called "Green Fuzzy" emission or "Extended Green Objects". We present color analysis of this emission toward six nearby (d=2-3 kpc) well-studied high-mass protostars and three candidate high-mass protostars identified with the Spitzer GLIMPSE survey. In our color-color diagrams most of the sources show a positive correlation between the [3.6]-[4.5] and [3.5]-[5.8] colors along the extinction vector in all or part of the region. We compare the colors with those of scattered continuum associated with the low-mass protostar L 1527, modeled scattered continuum in cavities, shocked emission associated with low-mass protostars, modeled H2 emission for thermal and fluorescent cases, and modeled PAH emission. Of the emission mechanisms discussed above, scattered continuum provides the simplest explanation for the observed linear correlation. In this case, the color variation within each object is attributed to different foreground extinctions at different positions. Alternative possible emission mechanisms to explain this correlation may be a combination of thermal and fluorescent H2 emission in shocks, and a combination of scattered continuum and thermal H2 emission, but detailed models or spectroscopic follow-up are required to further investigate this possibility. Our color-color diagrams also show possible contributions from PAHs in two objects. However, none of our sample show clear evidence for PAH emission directly associated with the high-mass protostars, several of which should be associated with ionizing radiation. This suggests that those protostars are heavily embedded even at mid-infrared wavelengths.Comment: 32 pages, 14 figures, 3 tables, accepted for publication in Astrophysical Journa

Utilization of ultra-thin n-type Hydrogenated Nanocrystalline Silicon for Silicon Heterojunction Solar Cells

To optimize the electrical performance of silicon heterojunction solar cell devices, the electronic properties and microstructure of n-type nc-Si:H were characterized and analyzed. It was found that higher conductivity and crystalline volume fraction (Fc) of nc-Si:H can be obtained at lower silane gas fraction (fSiH4), lower power and higher phosphorous gas fraction (fPH3). In our case, there is a decline of the passivation for the devices with nc-Si:H after sputtering process. By increasing the phosphine flow fraction, the sputter damage can be reduced and 3%abs gain of FF as well as 0.7%abs gain of efficiency is reached compared with reference. The best solar cell exhibits the Voc of 733.3 mV, FF of 79.7%, Jsc of 39.00 mA/cm2 and η of 22.79% at the M2 size wafer

Numerical study of Silicon Heterojunction Solar Cells with nc-SiC/SiO 2 Based Transparent Passivating Contact

Silicon heterojunction with nc-SiC(n)/SiO2 based front transparent passivating contact (TPC) is numerically modeled. The model is then used to study the effect of active dopant concentration at the front and rear contact of the solar cell. A potential of power conversion efficiency above 25 % can be achieved with a suitable acceptor dopant concentration of p-type amorphous silicon at the rear side. Improving fill factor via SiC dopant concentration can enhance the cell power conversion efficiency within a narrow range of active dopant concentration. However, very high doping of SiC can affect the cell performance negatively

A route towards high‐efficiency silicon heterojunction solar cells

In this work, we propose a route to achieve a certified efficiency of up to 24.51% for silicon heterojunction (SHJ) solar cell on a full-size n-type M2 monocrystalline-silicon Cz wafer (total area, 244.53 cm2) by mainly improving the design of the hydrogenated intrinsic amorphous silicon (a-Si:H) on the rear side of the solar cell and the back reflector. A dense second intrinsic a-Si:H layer with an optimized thickness can improve the vertical carrier transport, resulting in an improved fill factor (FF). In order to reduce the plasmonic absorption at the back reflector, a low-refractive-index magnesium fluoride (MgF2) is deposited before the Ag layer; this leads to an improved gain of short circuit current density (Jsc). In total, together with MgF2 double antireflection coating and other fine optimizations during cell fabrication process, ~1% absolute efficiency enhancement is finally obtained. A detailed loss analysis based on Quokka3 simulation is presented to confirm the design principles, which also gives an outlook of how to improve the efficiency further

Understanding Silicon Heterojunction Solar Cells with nc‐SiC/SiO 2 as an Alternate Transparent Passivating Front Contact and Computational Design Optimization

The potential performance of silicon heterojunction solar cells applying transparent passivating contact (TPC) at the front side, based on a nc-SiC:H/SiO2 layer stack, is modeled and investigated. Herein, a complete multiscale electro-optical device model of TPC solar cells is developed. The model is then used to understand and analyze such cells and search for potential conversion efficiency improvement paths. The influences of contact layer thicknesses and other properties on device performance are studied. An algorithm-based optimization of cell electro-optical performance is performed. It is implemented by coupling a genetic algorithm with a finite element method-based TPC solar cell device model. Optimum front contact layer thicknesses are calculated. For optically optimized TPC contact layer thicknesses, an optical improvement of around 0.5 mA cm² is found. Moreover, for complete electro-optical optimization of TPC layers, about 0.27% absolute value increment in power conversion efficiency is calculated. At the rear side, proper designing of optimizing carrier transport using active dopant concentration of p-type a-Si:H layer and indium tin oxide layer has shown a potential to reach power conversion efficiency beyond 25%

Function Analysis of the Phosphine Gas Flow for n-Type Nanocrystalline Silicon Oxide Layer in Silicon Heterojunction Solar Cells

The energy conversion efficiency (η) of silicon heterojunction (SHJ) solar cells is limited by the current losses in the layer stack on the illuminated side. To reduce these losses, hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) was implemented as a window layer in SHJ solar cells. However, the integration of nc-SiOx:H in devices without degradation of fill factor (FF) is still a challenge. To optimize the electron performance of devices, the optoelectronic properties and microstructure of nc-SiOx:H were characterized and analyzed systematically. It was found that the PH3 gas fraction (fPH3) plays a big role on the microstructure, oxygen content, and phosphorus (P) doping efficiency of the films. The highest conductivity, 2.84 × 10–1 S/cm, is obtained at a moderate fPH3 with an optical band gap of 2.26 eV. A ternary model was creatively used to show the variation in the composition of nc-SiOx:H as tuning fPH3. The growth of crystalline phase was accelerated by the P dopants when fPH3 is low, but further increasing fPH3 leads to excessive P inactive dopants, causing a phase transition from nanocrystalline silicon to amorphous silicon in nc-SiOx:H. In this work, the best solar cell with an nc-SiOx:H window layer achieves an FF of 81.4%, a short current density (Jsc) of 39.8 mA/cm2, an open-circuit voltage (Voc) of 731 mV, and an η of 23.7% at the moderate fPH3. A decrease in FF and Jsc is shown with higher fPH3, which is the consequence of the increased front contact resistivity and decreased optical band gap of nc-SiOx:H window layer

Improved Infrared Light Management with Transparent Conductive Oxide/Amorphous Silicon Back Reflector in High‐Efficiency Silicon Heterojunction Solar Cells

To improve the infrared (IR) response, a high-refractive-index intrinsic amorphous silicon (a-Si:H) layer is introduced after metallization of bifacial silicon heterojunction (SHJ) solar cells, resulting in a transparent conductive oxide (TCO)/a-Si:H back reflector, which functions like distributed Bragg reflector (DBR). This concept is demonstrated by both Sentaurus Technology Computer-Aided Design (TCAD) simulation and experimental methods. The TCO/a-Si:H back reflector can increase rear internal reflectance by reducing the transmission loss, thus improving the IR external quantum efficiency. The using of Sn-doped In2O3 (ITO)/a-Si:H back reflector in >23.5% efficiency SHJ solar cells can improve short-circuit current density by 0.4 mA cm2 which is quite similar as using the more expensive ITO/Ag back reflector, while keeping a cell bifaciality of 55%. This brings its advantage for monofacial application case. Future studies would be nice to work on higher transparent back reflectors to broaden the application in bifacial case. This back-reflector design promotes IR response of SHJ solar cells with transferring to a wide variety of TCOs