High-quality Passivation Layer Research Articles

Dense Amorphous Passivation Layer Formed on Aluminum Alloy Surfaces by Femtosecond Laser-Assisted Oxygen-Rich Doping.

Aluminum (Al) alloy surfaces are prone to serious corrosion in humid and salt-laden environments, which promotes the development of numerous protective approaches. Although the amorphous state is more conducive to improve corrosion resistance compared with the crystalline state, it still faces coating design problems like insufficient adhesive strength and flaking-off tendency. Here, we propose a strategy of femtosecond laser-assisted oxygen-rich doping to in situ create a dense high-quality passivation layer on Al alloy surfaces. With respect to the femtosecond laser processing in traditional air ambience, the material surface modifications within the oxygen-rich environment demonstrate some distinctiveness. For the ridge area of the laser ablation grooves, the oxidation surface is separated into two layers: the outer region presents a loose and porous appearance similar to the observations in the air ambience, while the inner region exhibits complete and homogeneous oxidation, especially associated with the continuous distribution of the amorphous substance, in sharp contrast to the nanoscale discrete amorphous formation in the air case. Simultaneously, the high degree of material oxidization with the amorphous phase is also developed on the wallside area of the groove valleys, which is much different from the incomplete oxidation in the air ambience. As a result, the measured corrosion current decreases by 49 times to a value of Icorr = 1.19 × 10-10 A/cm2 relative to the laser treatment in the air environment. Such a method offers the prospect for elevating the anticorrosion performance of metal surfaces.

Improving Electrical Stability of a-InGaZnO Thin-Film Transistors with Thermally Deposited Self-Assembled Monolayers

Amorphous InGaZnO (a-IGZO) TFTs become mainstream at the forefront of display backplanes and are actively expanding their area for next-generation optoelectronic devices such as flexible and transparent displays. For flexible displays, low temperature processed passivation technology is required to keep the reliability of the electrical properties in a-IGZO TFTs without damaging flexible plastic substrates. Here, we proposed a low-temperature passivation process using a dual-chamber system. A high-quality passivation layer composed of octadecyl-trichlorosilane was formed at 140 °C under vacuum on the back-channel of a-IGZO TFTs using the system. The thermally deposited self-assembled monolayers (SAMs) enable the formation of hydrophobic surfaces on a-IGZO TFTs, leading to the protection of the back-channel against water and oxygen efficiently. As a result, the electrical characteristics such as the threshold voltage shift, hysteresis, field-effect mobility, and negative bias stress of the SAM treated TFTs were significantly improved compared to those of the control TFTs.

H2O/O2 Vapor Annealing Effect on Spin Coating Alumina Thin Films for Passivation of Silicon Solar Cells

Aluminum acetylacetonate-based AlOx thin films were introduced as a low-cost, high-quality passivation layers for crystalline silicon solar cells. Films were formed by a spin coating method on p-type silicon substrates at 450°C in ambient air, O2, or water vapor (H2O/O2) for 15 or 120 min. XPS analysis confirms the AlOx formation and reveals a high intensity of interfacial SiOx at the AlOx/Si interface of processed wafers. Ambient H2O/O2 was found to be more beneficial for the activation of introduced AlOx passivation films which offers high lifetime improvements with a low thermal budget. Carrier lifetime measurements provides that symmetrically coated wafers reach 119.3 μs and 248.3 μs after annealing in ambient H2O/O2 for 15 min and 120 min, respectively.

Surface depletion effect on negative bias stress instability of β-Ga2O3 (100) nanomembrane FETs

In this study, we report on negative bias stress (NBS) instability of bottom-gate β-Ga2O3 (100) field-effect transistors and the effect of surface states reduction by using an atomic layer deposited Al2O3 layer. The fabricated devices exhibit high electrical performance with a field-effect mobility of up to 71.6 cm2 V−1 · s−1 and a subthreshold slope of ∼0.2 V dec−1. However, the abnormal positive threshold voltage (VTH) shifts under NBS conditions were observed. These phenomena, resulting from the surface depletion effect due to surface defects including dangling bonds and surface states, were moderated and thus the positive VTH shift was altered into a conventional negative shift by using ALD-Al2O3 surface passivation. The results indicate that a high quality passivation layer is suggested to ensure β-Ga2O3 device performance and stability.

>21% Efficient Silicon Heterojunction Solar Cells on n- and p-Type Wafers Compared

The properties and high-efficiency potential of front- and rear-emitter silicon heterojunction solar cells on n- and p-type wafers were experimentally investigated. In the low-carrier-injection range, cells on p-type wafers suffer from reduced minority carrier lifetime, mainly due to the asymmetry in interface defect capture cross sections. This leads to slightly lower fill factors than for n-type cells. By using high-quality passivation layers, however, these losses can be minimized. High open-circuit voltages (Vocs) were obtained on both types of float zone (FZ) wafers: up to 735 mV on n-type and 726 mV on p-type. The best Voc measured on Czochralski (CZ) p-type wafers was only 692 mV, whereas it reached 732 mV on CZ n-type. The highest aperture-area certified efficiencies obtained on 4 cm2 cells were 22.14% (Voc = 727 mV , FF = 78.4%) and 21.38% (Voc = 722 mV, FF = 77.1%) on n- and p-type FZ wafers, respectively, proving that heterojunction schemes can perform almost as well on high-quality p-type as on n-type wafers. To our knowledge, this is the highest efficiency ever reported for a full silicon heterojunction solar cell on a p-type wafer, and the highest Voc on any p-type crystalline silicon device with reasonable FF.

Material Research on High-Quality Passivation Layers with Controlled Fixed Charge for Crystalline Silicon Solar Cells

Material Research on High-Quality Passivation Layers with Controlled Fixed Charge for Crystalline Silicon Solar Cells

Material Research on High-Quality Passivation Layers with Controlled Fixed Charge for Crystalline Silicon Solar Cells

We evaluated the three types of composition spread passivation layer, i.e., Al2O3–HfO2, HfO2–Y2O3, and Al2O3–Y2O3 systems, by combinatorial pulsed laser deposition to evaluate and control the fixed charge, while interface states were kept constant with a SiO2 interlayer. The flat-band voltage of the capacitance–voltage (C–V) curves was shifted widely from positive to negative by changing the composition. The calculated fixed charge in the Y2O3 was positive while those in the HfO2 and Al2O3 were negative. In the Al2O3–Y2O3 system, the fixed charge was significantly varied between -2.7 and 1.3×1012 cm-2 with composition spread. The maximum negative charge was found in the Al2O3 layer with a slight amount of Y2O3, while the maximum positive charge was realized with almost pure Y2O3. The fixed charge modifications were also found in the Al2O3–HfO2 and HfO2–Y2O3 systems. Additional oxidation after layer deposition also modified the fixed charge properties. The largest negative fixed charge of -3.1×1012 cm-2 was found in approximately HfO2:Y2O3=1:1 after the annealing process, while the largest positive charge of 1.3×1012 cm-2 was found for Y2O3 with Al2O3 incorporation. The passivation layers with controlled fixed charge can be promising materials for the high-quality passivation layer in crystalline silicon solar cells.