Sputtered Tungsten Oxide as Hole Contact for Silicon Heterojunction Solar Cells

Reactively sputtered tungsten oxide WOx was investigated as hole contact on n type crystalline silicon. Varying the oxygen gas flow during sputtering enables variation of the WOx conductivity from 0.01 to 1000 amp; 937; cm, while the band bending at the interface and the implied fill factor FF change by 70 meV and 1.5 . SputteredWOx shows higher resistivity and higher absorption in the visible range compared with indium tin oxide ITO . Therefore, stacks of WOx and ITO are used in solar cells. It was found that at least 20 nm thick WOx is needed to prevent detrimental effects of the ITO work function on the band bending at the junction, the implied FF, and the real FF of solar cells. WOx hole contacts of different thicknesses and conductivity were applied in solar cells and it was found that the highest FF is achieved using about 20 nm thick interlayers of WOx with the highest possible conductivity. It was found that sputtering enables a drastic improvement of WOx silicon solar cells compared with thermal evaporation, due to the precise control of the WOx conductivity. Unfortunately, the resistivity of the sputteredWOx is still limiting the FF of these device

Oxygen vacancies in tungsten oxide and their influence on tungsten oxide silicon heterojunction solar cells

Tungsten oxide WOx can be incorporated into amorphous crystalline silicon heterojunction solar cells as hole contact and for interface modification between p type amorphous silicon and indium tin oxide. This paper aims at understanding the influence of tungsten oxides properties on silicon heterojunction solar cells. Using in system photoelectron spectroscopy on thermally evaporated WOx layers, it was verified that WOx with a stoichiometry close to WO3 features a work function close to 6 eV and is therefore suitable as hole contact on silicon. Additionally the oxygen vacancy concentration in WOx was measured using photoelectron spectroscopy. High oxygen vacancy concentrations in WOx lead to a low band bending in the WOx silicon junction. Furthermore solar cells were fabricated using the same WOx, and the band bending in these cells is correlated with their fill factors FF and open circuit voltages VOC VOC . Combining these results, the following picture arises positively charged oxygen vacancies raise the Fermi level in WOx and reduce the band bending at the WOx silicon junction. This, in turn, leads to reduced VOCVOC and FF. Thus, when incorporating WOx into silicon solar cells it is important to minimize the oxygen vacancy density in WOx. Therefore deposition methods, enabling adjustment of the WOx stoichiometry are preferabl

Valence band alignment and hole transport in amorphous crystalline silicon heterojunction solar cells

To investigate the hole transport across amorphous crystalline silicon heterojunctions, solar cells with varying band offsets were fabricated using amorphous silicon suboxide films. The suboxides enable good passivation if covered by a doped amorphous silicon layer. Increasing valence band offsets yield rising hole transport barriers and reduced device effciencies. Carrier transport by thermal emission is reduced and tunnel hopping through valence band tail states increases for larger barriers. Nevertheless, stacks of films with different band gaps, forming a band offset staircase at the heterojunction could allow the application of these layers in silicon heterojunction solar cell

Electronic structure of indium tungsten oxide alloys and their energy band alignment at the heterojunction to crystalline silicon

The electronic structure of thermally co evaporated indium tungsten oxide films is investigated. The stoichiometry is varied from pure tungsten oxide to pure indium oxide and the band alignment at the indium tungsten oxide crystalline silicon heterointerface is monitored. Using in system photoelectron spectroscopy, optical spectroscopy and surface photovoltage measurements we show that the work function of indium tungsten oxide continuously decreases from 6.3 eV for tungsten oxide to 4.3 eV for indium oxide, with a concomitant decrease of the band bending at the hetero interface to crystalline silicon than indium oxid

An innovative radiation hardened CAM architecture

An innovative Content Addressable Memory (CAM) cell with radiation hardened (RH) architecture is presented. The RH-CAM is designed using a commercial 28 nm CMOS technology. The circuit has been simulated in worst-case conditions, and the effects due to single particles have been analyzed by injecting a current pulse into a circuit node. The proposed architecture is suitable for real-time pattern recognition tasks in harsh environments, such as front-end electronics in the ATLAS experiment at the Large Hadron Collider (LHC) and in space applications

Amorphous crystalline silicon heterojunction solar cells with black silicon texture

Excellent passivation of black silicon surfaces by thin amorphous silicon layers deposited with plasma enhanced chemical vapor deposition is demonstrated. Minority charge carrier lifetimes of 1.3 milliseconds, enabling an implied open circuit voltage of 714 mV, were achieved. The influence of amorphous silicon parasitic epitaxial growth and thickness, as well as of the texture depth is investigated. Furthermore quantum efficiency gains for wavelenghts above 600 ,nm, as compared to random textured solar cells, are demonstrated in 17.2 efficient amorphous crystalline silicon heterojunction solar cells with black silicon textur

In system photoelectron spectroscopy study of tin oxide layers produced from tetrakis dimethylamino tin by plasma enhanced atomic layer deposition

Tin oxide SnO2 layers were deposited using plasma enhanced atomic layer deposition with tetrakis dimethylamino tin precursor and oxygen plasma. The deposited layers were analyzed by spectral ellipsometry, conductivity measurements, and in system photoelectron spectroscopy. Within a deposition temperature range of 90 210 amp; 8201; C, the resistivity of the SnO2 layers decreases by 5 orders of magnitude with increasing deposition temperature. At the same time, the refractive index at 632.8 amp; 8201;nm increases from 1.7 to 1.9. These changes in bulk layer properties are connected to results from photoelectron spectroscopy. It is found that decreasing carbon and nitrogen contaminations in the tin oxide layers lead to decreasing optical band gaps and increasing refractive index. Additionally, for the deposited SnO2 layers, a shoulder in the O 1s core level spectrum is observed that decreases with the deposition temperature and thus is proposed to be related to hydroxyl group

A Review of Brittleness Index Correlations for Unconventional Tight and Ultra-Tight Reservoirs

Brittleness is a key parameter in the development of the unconventional shale and tight carbonate reservoirs as it plays a role in the design of the hydraulic fractures as well as the selection of the sweet-spot locations for perforation and fracture initiation. The brittleness index (BI) is utilized to indicate if the formation rocks are brittle, which are preferable to form a complex network of fractures, or ductile, which are occasionally desirable to seal the fractures from growing. However, there is a wide variety of BI methods in the literature that lead to inconclusive BI values. The Mineral-based brittleness index (MBI), which is a method based on the mineral composition of the formation, can be derived from mineral well logging data or laboratory core testing. Another approach in describing the brittleness is the Fracability Index (FI), which is a combination of Young’s modulus and Poisson’s ratio. Differentiation is also made between the dynamic FI, which is calculated from well logging data, and the static FI, which is derived from laboratory core testing such as uniaxial compressive strength, Brazilian tensile strength and triaxial testing. Hence, to understand the complexity of the brittleness, it is crucial to consider all dependencies such as the lithology, mineral composition, TOC, porosity, temperature and pressure amongst others. In this work, a comprehensive review and analysis of the existing equations and correlations for the calculation of the MBI and FI was conducted. These methods were applied on different low porosity and low permeability rocks. A thorough comparison has also been conducted between the MBI and FI correlations as well as between the dynamic FI and the static FI to ultimately clarify and improve the definition of brittleness as a function of lithology. High content of quartz and carbonates result in high values of MBI, and high Young’s modulus values yield high FI values. On the other hand, high clay content and high porosity lead to low MBI values

Valence band offset and hole transport across a SiOx 0 lt;x lt;2 passivation layers in silicon heterojunction solar cells

In this work, the valence band offset amp; 916;EV and hole transport across the heterojunction between amorphous silicon suboxides a SiOx H and crystalline silicon c Si is investigated. Thin layers ranging from pure intrinsic a Si H to near stoichiometric a SiO2 were grown by varying precursor gas mixtures during chemical vapor deposition. A continuous increase of amp; 916;EV starting from amp; 8776; 0 .3 eV for the a Si H c Si to gt; 4 eV for the a SiO2 c Si heterointerface was measured by in system photoelectron spectroscopy. Furthermore, p a Si H i a SiOx H n c Si i,n a Si H heterojunction solar cells, with intrinsic a SiOx H passivation layers deposited using the same parameter sets, were fabricated. We report a linear decrease of the solar cell fill factor for increasing amp; 916;EV in the range of 0.27 0.85 eV. The reason is an increase of the barrier height for holes at the i a SiOx H n c Si heterojunction and a simultaneous change of the hole transport mechanism from thermionic emission to defect assisted tunnel hopping through valence band tail states. It is demonstrated that as compared to a single layer, significantly larger barrier heights can be tolerated in a stack of high band gap material and a material with lower band gap, forming a staircase of band offsets. This could allow the application of these layers in silicon heterojunction solar cell