Effective Carrier Lifetime Research Articles

Improved performance of silicon heterojunction solar cells via 3× three-step boron-doping

To improve the doping efficiency of boron (B)-doped hydrogenated amorphous silicon [a-Si:H(p)] films, a three-step post-B-doping method was developed. This post-treatment method presents the potential to enhance not only the B content but also the hydrogen content in a-Si:H(p) films by increasing the number of treatment times. Based on secondary ion mass spectroscopy and dark conductivity measurements, the B concentration and efficiency of B-doping in a-Si:H(p) films were effectively improved by the three-step B-doping treatment. Furthermore, it was demonstrated that the atomic hydrogen generated during the B-doping process could diffuse into the a-Si:H(p) film and the underlying a-Si:H(i) layers, which is beneficial for suppressing the carrier recombination in the a-Si:H(p/i) passivation layers. There was an absolute increase of 600 μs in the effective minority carrier lifetime in the standard a-Si:H(n)/a-Si:H(i)/c-Si(n)/a-Si:H(i)/a-Si:H(p) structure by the 3× three-step treatment on the emitter side. Consequently, enhancements in both the open circuit voltage and the fill factor were observed, resulting in a 0.28% absolute gain (approximately) in the conversion efficiency of silicon heterojunction cells.

20 kV-Class Ultra-High Voltage 4H-SiC n-IE-IGBTs

We demonstrate 20 kV-class 4H-SiC n-channel implantation and epitaxial (IE)-IGBTs having both low on-state voltage and high blocking characteristics. We fabricated n-IE-IGBTs on a (0001) silicon face with free-standing epitaxial layers. Effective carrier lifetime increased significantly from 0.9 μs to 9.6 μs by a lifetime enhancement process. We used the IE structure to suppress an increase of the surface p+-well concentration, reduce implantation damage at the p+-well, and reduce junction field effect transistor (JFET) region resistance by ion implantation as a counter doping. The n-IE-IGBT at 100 A/cm2 on-state voltage and specific differential on-resistance was 8.2 V and 36.9 mΩcm2, respectively, at room temperature with a 30 V gate voltage. The blocking voltage was 26.8 kV at 45.7 μA.

Effect of thermally annealed atomic-layer-deposited AlOx/chemical tunnel oxide stack layer at the PEDOT:PSS/n-type Si interface to improve its junction quality

We investigated the effects of thermal annealing on an atomic layer deposition-fabricated AlOx/chemical tunnel oxide (ch-SiOx) stack layer, for passivating and enhancing the field-inversion at the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/n-type crystalline Si (n-Si) interface. Annealing in N2/H2 forming gas at 560 °C for 30 min increased the effective minority carrier lifetime (τeff) of the AlOx/ch-SiOx stack layer to 300–331 μs, which decreased sheet resistance and enhanced the built-in potential and open-circuit voltage in PEDOT:PSS/n-Si heterojunction solar cells to 750 mV and 645 mV, respectively. These improvements originate from the local chemical bond configuration of the tunnel oxide ch-SiOx, which determines the passivation ability and band alignment at the AlOx/n-Si interface.

Hydrogen-rich c-Si interfacial modification to obtain efficient passivation for silicon heterojunction solar cell

How to passivate the heterojunction between the doped layer and the crystalline silicon (c-Si) base plays a crucial role for the silicon heterojunction (SHJ) solar cell to obtain high performance, especially high open-circuit voltage (VOC) and fill factor (FF). Here, a hydrogen-rich c-Si interfacial modification was realized by preparing an ultrathin (~ 1.5 nm) intrinsic hydrogenated amorphous silicon (a-Si:H) onto the c-Si(n) interface with pure silane via plasma enhanced chemical vapor deposition (PECVD), prior to the deposition of a ~ 8 nm relatively compact a-Si:H(i) layer for the a-Si:H(p)/c-Si(n) heterojunction. The enhanced effective minority carrier lifetime (τeff) of the c-Si base and VOC of the final solar cell indicated that such interfacial modification improved the heterojunction passivation efficiently by saturating the c-Si dangling bonds (DBs) via hydrogenation with the following deposition of the compact a-Si:H(i) layer that kept the c-Si interface out of direct contact with the doped layer. By altering the deposition pressure, the hydrogen content (CH) in the ultrathin a-Si:H was adjusted regularly to fabricate a series of SHJ solar cells with the area of 244.45 cm2. A maximal conversion efficiency up to 23.81% was achieved with VOC of 742.9 mV, JSC of 38.67 mA/cm2 and FF of 82.99% when the ultrathin a-Si:H had a relatively high CH of about 24–25%.

Laser Crystallization and Dopant Activation of a-Si:H Carrier-Selective Layer in TOPCon Si Solar Cells

Herein, we present a pulsed-laser processing method for crystallization and dopant activation of a highly n-doped amorphous silicon (a-Si:H) carrier-selective layer in a tunnel oxide passivated contact (TOPCon) Si solar cell structure. The laser method provides enhanced conductivity and implied open circuit voltage while reducing emitter saturation current density and surface heating, as opposed to conventional high-temperature furnace annealing of the bulk Si wafer with a TOPCon structure. We identify an appropriate laser wavelength, fluence, and layer thickness using modeling and simulations. Raman and Hall effect measurements demonstrate increased crystallinity and dopant activation, whereas photoconductive decay shows enhanced surface and interface passivation quality. Additionally, we examine the role of subsequent SiNx deposition on further improving the passivation of laser-processed TOPCon layers to achieve a 5.9 kΩ/sq film sheet resistance, 2 ms effective carrier lifetime, 718 mV implied open-circuit voltage (iVOC), and 8.6 fA/cm2 one-side recombination current density (J0) with the potential for further passivation improvement via laser process and a-Si layer thickness optimization.

Improving the Passivation of Molybdenum Oxide Hole‐Selective Contacts with 1 nm Hydrogenated Aluminum Oxide Films for Silicon Solar Cells

The intrinsic and doped amorphous silicon layers in silicon heterojunction solar cells parasitically absorb light in the short wavelength region of the solar spectrum, lowering the generation current available to the device. Herein, a promising alternative to the hole‐selective amorphous silicon contact layers using only wide bandgap, transparent oxide materials is presented. Using thermal atomic layer deposition, a 1 nm hydrogenated aluminum oxide layer is deposited followed by a 4 nm molybdenum oxide layer on n‐type crystalline silicon. This contact stack provides an effective carrier lifetime of 1.14 ms. It is shown that the molybdenum oxide layer is successfully deposited with a high work function, which facilitates efficient hole extraction and repels majority carriers from the c‐Si surface. Then the implied open‐circuit voltage, saturation current density, and contact resistivity are recorded as a function of contact annealing temperature and show that they are relatively stable up to 200 °C.

Prospect of CW Raman Laser in Silicon- on- Insulator Nano-Waveguides


 Numerical analysis predicts that continuous-wave (CW) Raman lasing is possible in Silicon-On-insulator (SOI) nano-waveguides, despite of presence of free carrier absorption. The scope of this paper lies on lasers for communication systems around 1550 nm wavelength. Two types of waveguide structures Strip and Rib waveguides have been incorporated. The waveguide structures have designed to be 220 nm in height. Three different widths of (350, 450, 1000) nm were studied. The dependence of lasing of the SOI Raman laser on effective carrier lifetime was discussed, produced by tow photon absorption. At telecommunication wavelength of 1550 nm, Raman lasing threshold was calculated to be 1.7 mW in Rib SOI waveguide with dimensions width (W= 450 nm) and Length (L= 25 mm). The obtained Raman lasing is the lowest reported value at relatively high reflectivities. Raman laser in SOI nano-waveguides presents the important step towards integrated on-chip optoelectronic devices.

Dark current analysis of germanium-on-insulator vertical p-i-n photodetectors with varying threading dislocation density

Dark current characteristics of germanium (Ge) vertical p-i-n photodetectors were studied. Ge photodetectors were demonstrated on the germanium-on-insulator (GOI) platforms realized via direct wafer bonding and layer transfer. GOI platforms with two different threading dislocation densities (TDDs) of 3.2 × 106 cm−2 (low TDD) and 5.2 × 108 cm−2 (high TDD) were varied via furnace annealing in oxygen ambient. An ultra-low dark current density of 1.12 mA/cm2 for epi-Ge photodetectors was obtained for a low TDD Ge photodetector. This is reduced by a factor of 53 in comparison with a high TDD Ge photodetector. A dominant leakage contribution component shifts from bulk leakage to surface leakage as TDD decreases to 3.2 × 106 cm−2, suggesting that advanced surface passivation is required to further reduce the leakage current. Through an activation energy study, it is revealed that a primary bulk leakage mechanism shifts from Shockley–Read–Hall (SRH) leakage to diffusion leakage in a temperature range of 323–353 K. The surface leakage performed with plasma enhanced chemical vapor deposition-deposited SiO2 is governed by SRH and trap-assisted tunneling leakage processes. Two orders of magnitude enhancement in the effective carrier lifetime is observed with the reduction in TDD. This work suggests that bulk leakage current density and effective lifetime analysis provide a better understanding of TDD-dependent dark leakage current study.

Surface related degradation phenomena in P-type multi-crystalline silicon at elevated temperature and illumination

As a non-negligible part of light and elevated temperature induced degradation (LeTID), the studies of surface related degradation are rare, and the complex mechanism hinders the research in this field. In this paper, the degradation behaviors of passivation quality on the surface of P-type multi-crystalline silicon were mainly analyzed during LeTID. Results shown that effective minority carrier lifetime of passivated mc-Si wafers decreased in the range of 20–50% after it got to the full degraded during light soaking at 80 °C. The fixed charges at the interface between passivation layer and silicon bulk increased slightly after full degradation, which had little effect on field-effect passivation. Long-term illumination resulted in a certain increase in interface states density (Dit) in the bottom half of bandgap. According to the result that the increment of Dit of ungettered samples was higher than that of phosphorus diffusion gettered samples, it implied that the increase of interface defects might be caused by the diffuse of impurities in the bulk to the surface during the process of LeTID.

The impact of interstitial Fe contamination on n-type Cz-Silicon for high efficiency solar cells

In this work, we have investigated the impact of interstitial Fe contamination on the effective minority carrier lifetime of n-type Cz silicon bulk material for high efficiency solar cells. The study covers a Fe concentration in the silicon bulk from 3.5 × 1012 cm-3 to 2.7 × 1014cm-3. We have added 5 different concentrations (30, 100, 300, 1000 and 3000 ppb) of Fe intentionally to a wet chemical process tank and measured the transfer to the silicon wafer surface mimicking a possible contamination during wet chemical processing. In order to fabricate carrier lifetime test vehicles, the silicon wafer is then passivated with thermal silicon oxide from both sides. The surface contamination is driven into the bulk by mimicking a high temperature process during solar cell manufacturing. Effective minority carrier lifetime is measured at injection levels from 1 × 1013 cm-3 to 3 × 1015cm-3. We have fitted the theoretical curve for interstitial Fe derived from the SRH theory to the measured values and extracted the Fe contamination concentration. This value is comparable to the calculated value extracted from the surface contamination measurement. For low level injection (LLI), we extracted the capture cross section for interstitial Fe to be 6.45 × 10-17 cm/s ± 2.23 × 10-17 cm/s. The measured Fe contamination levels are used for the conversion efficiency fitting of a n-type bifacial silicon solar cell using QUOKKA simulations. The simulations show that very low Fe contamination concentrations of [Fe]bulk = 3.5 × 1012 cm-3 ([Fe]surf = 6 × 1010cm-2) already degrade the solar cell efficiency by 10% relative.

Wet Chemical Oxidation to Improve Interfacial Properties of Al2O3/Si and Interface Analysis of Al2O3/SiOx/Si Structure Using Surface Carrier Lifetime Simulation and Capacitance–Voltage Measurement

A thin silicon oxide (SiOx) layer (thickness: 1.5–2.0 nm) formed at an Al2O3/Si interface can enhance the interface properties. However, it is challenging to control the characteristics of thin SiOx layers because SiOx forms naturally during Al2O3 deposition on Si substrates. In this study, a ~1.5 nm-thick SiOx layer was inserted between Al2O3 and Si substrates by wet chemical oxidation to improve the passivation properties. The acidic solutions used for wet chemical oxidation were HCl:H2O2:H2O, H2SO4:H2O2:H2O, and HNO3. The thicknesses of SiOx layers formed in the acidic solutions were ~1.48, ~1.32, and ~1.50 nm for SiOx-HCl, SiOx-H2SO4, and SiOx-HNO3, respectively. The leakage current characteristics of SiOx-HNO3 were better than those of the oxide layers formed in the other acidic solutions. After depositing a ~10 nm-thick Al2O3 on an SiOx-acidic/Si structure, we measured the effective carrier lifetime using quasi steady-state photoconductance and examined the interfacial properties of Al2O3/SiOx-acidic/Si using surface carrier lifetime simulation and capacitance–voltage measurement. The effective carrier lifetime of Al2O3/SiOx-HNO3/Si was relatively high (~400 μs), resulting from the low surface defect density (2.35–2.88 × 1010 cm−2eV−1). The oxide layer inserted between Al2O3 and Si substrates by wet chemical oxidation helped improve the Al2O3/Si interface properties.

Role of Underlayer for Efficient Core-Shell InGaN QWs Grown on m-plane GaN Wire Sidewalls.

Different types of buffer layers such as InGaN underlayer (UL) and InGaN/GaN superlattices are now well-known to significantly improve the efficiency of c-plane InGaN/GaN-based light-emitting diodes (LEDs). The present work investigates the role of two different kinds of pregrowth layers (low In-content InGaN UL and GaN UL namely "GaN spacer") on the emission of the core-shell m-plane InGaN/GaN single quantum well (QW) grown around Si-doped c̅-GaN microwires obtained by silane-assisted metal organic vapor phase epitaxy. According to photo- and cathodoluminescence measurements performed at room temperature, an improved efficiency of light emission at 435 nm with internal quantum efficiency >15% has been achieved by adding a GaN spacer prior to the growth of QW. As revealed by scanning transmission electron microscopy, an ultrathin residual layer containing Si located at the wire sidewall surfaces favors the formation of high density of extended defects nucleated at the first InGaN QW. This contaminated residual incorporation is buried by the growth of the GaN spacer and avoids the structural defect formation, therefore explaining the improved optical efficiency. No further improvement is observed by adding the InGaN UL to the structure, which is confirmed by comparable values of the effective carrier lifetime estimated from time-resolved experiments. Contrary to the case of planar c-plane QW where the improved efficiency is attributed to a strong decrease of point defects, the addition of an InGaN UL seems to have no influence in the case of radial m-plane QW.

Effective minority carrier lifetime in double-sided macroporous silicon

Effective minority carrier lifetime in double-sided macroporous silicon

Impact of Ge deposition temperature on parameters of c-Si solar cells with surface texture formed by etching of Si using SiGe islands as a mask

In this paper, the Ge self-assembled islands grown at different temperatures were used as an etching mask for selective anisotropic etching of crystalline silicon (c-Si) in order to form a textured Si surface. The effects of Ge deposition temperature on the texture morphology as well as the parameters of c-Si solar cells fabricated on such structures were studied with the range of temperature from 500 °C to 800 °C. The textures on Si surface with low (<1 μm) etching margin were successfully fabricated for all investigated structures. It was revealed that usage of rapid annealing of Si wafer at 800 °C prior to epitaxial growth along with the low Ge deposition temperature of 500 °C allowed to achieve the relatively high effective carrier lifetime as compared to structures formed at higher (≥700 °C) temperatures thanks to the reduced degradation of Si wafer characteristics. Furthermore, the structure obtained using the lowest deposition temperature of 500 °C exhibited the highest light absorption among all studied samples thanks to the most homogeneous and most pyramidal texture morphology. As a result, the calculated short circuit current density JSC for the sample in which Ge islands were grown at 500 °C was as high as 35.89 mA/cm2. The proposed approach of surface texturing meets the requirements for thin c-Si solar cells due to small etching margin and the obtained results pave the way for increase the efficiency of thin c-Si solar cells by engineering the surface morphology to improve light absorption.

Optoelectrical properties of high-performance low-pressure chemical vapor deposited phosphorus-doped polysilicon layers for passivating contact solar cells

We examine the optical behavior and electrical performance of ultra-thin interfacial oxide (iOx) and polysilicon (poly-Si) layers deposited using industrial tube-type low-pressure chemical vapor deposition (LPCVD). The intrinsic and doped poly-Si layers of different thicknesses are examined for their optical, electrical and passivation properties at different conditions. We present an outstanding surface passivation result with in-situ iOx and n+doped poly-Si layers of thickness ranging from 150 nm to 250 nm. Intrinsic poly-Si layers are deposited using LPCVD and doped at high temperature in a tube furnace. An excellent effective minority carrier lifetime of 17 ms, implied open-circuit voltage of 747 mV and an ultralow dark saturation current density of 1.2 fA/cm2 are obtained for a 150 nm thick n+ poly-Si after fast-firing at a peak temperature of 745 °C.

Effects of x-ray irradiation on charge transport and charge collection efficiency in stabilized a-Se photoconductors

Stabilized amorphous selenium (a-Se) photoconductive layers are currently used in the majority of modern digital x-ray flat panel imaging detectors in mammography. We examine the effects of pre-exposure of a-Se to high-dose x-ray irradiation on both hole and electron lifetimes, τe and τh, respectively, without any field applied to the device. The x-ray irradiation was from an Al-filtered tungsten target x-ray tube. We show that reduction in τh and τe depends only on the total or accumulated dose, D, absorbed in a-Se, and not on the rate of dose delivery, dD/dt, over the range of 0.15 Gy/s–2.5 Gy/s or on the x-ray energy over 50–90 kVp, corresponding to a mean photon energy over 31.9 keV–44.7 keV. The x-ray induced effects on charge transport are independent of the x-ray intensity and x-ray photon energy but dependent on the total energy absorbed in a-Se. The latter finding allows x-ray induced drop in the carrier lifetimes to be simply and conveniently modeled by τo/τ = 1 + AD, where τo is the lifetime before x-ray exposure (equilibrium lifetime), τ is the lifetime after exposure, D is the absorbed total dose, and A is a constant, which is 0.203 (±0.021) Gy−1 for the hole lifetime and 0.0620 (±0.0090) Gy−1 for the electron lifetime, a factor of three smaller than that for holes. X-ray irradiation had no effect on hole and electron drift mobilities. Reduction in carrier lifetimes with the total dose was examined at 10 °C, 23.5 °C, and 35.5 °C, close to the glass transition temperature, where x-ray induced effects are stronger. A is independent of hole and electron lifetimes but has a strong temperature dependence, increasing sharply with temperature. After the cessation of x-ray irradiation, carrier lifetimes relax (increase) to their pre-exposed equilibrium values over time scales that depend on temperature. Recovery has been interpreted and analyzed in terms of considering the kinetics of the rate at which x-ray induced capture centers are removed, as the structure restores the equilibrium concentration of deep traps. The annealing process of excess hole traps has a fast and a slow decay component, with time constants τr1 and τr2, respectively. The recovery processes associated with τr1 and τr2 exhibit activation energies larger than those typically involved in electronic transitions and are comparable to bond breaking energies in Se–Se and Se–As. Near 35.5 °C, close to the glass transition temperature, τr2-recovery has a large activation energy, pointing to structural relaxation phenomena. Fast annealing (∼6 min) of excess hole traps at 35.5 °C is, in a general sense, in agreement with the disappearance of irreversible photoinduced effects and suppression of crystallization (strain relief) at the a-Se/substrate interface, as observed previously. In the case of recovery of the electron lifetime, single exponential decay in excess electron traps and clear activation energy of 1.91 eV/atom point to a probable Se–Se bond breaking involved in returning excess electron traps to equilibrium concentration. Interpretations based on x-ray induced excess valence alternation pair (VAP) and intimate VAP type defects are also considered, including conversion from neutral defects to charged VAP defects. The implications of the present findings on x-ray sensitivity of a-Se detectors through the charge collection efficiency (CCE) are also examined and discussed. An effective carrier lifetime concept is used to describe the effect of x-ray irradiation on carrier lifetimes, which is then used to find CCE in a pre-exposed a-Se detector. The results indicate that x-ray induced effects are negligible for nearly all practical applications of a-Se mammographic detectors in use provided that the detector is operated at a sufficiently high field and a-Se has sufficiently long initial lifetimes, i.e., it is a high quality electronic grade material.

Electron and proton irradiation effect on the minority carrier lifetime in SiC passivated p-doped Ge wafers for space photovoltaics

We report on the effect of electron and proton irradiation on effective minority carrier lifetimes (τeff) in p-type Ge wafers. Minority carrier lifetimes are assessed using the microwave-detected photoconductance decay (μW-PCD) method. We examine the dependence of τeff on the p-type doping level and on electron and proton radiation fluences at 1 MeV. The measured τeff before and after irradiation are used to estimate the minority carriers’ diffusion lengths, which is an important parameter for solar cell operation. We observe τeff ranging from ≈ 50 to 230 μs for Ge doping levels between 1 × 1017 and 1 × 1016 at.cm−3, corresponding to diffusion lengths of ≈ 500–1400 μm. A separation of τeff in Ge bulk lifetime and surface recombination velocity is conducted by irradiating Ge lifetime samples of different thicknesses. The possible radiation-induced defects are discussed on the basis of literature.

Effect of forming gas annealing on hydrogen content and surface morphology of titanium oxide coated crystalline silicon heterocontacts

Crystalline silicon (c-Si) heterojunction solar cells using carrier-selective contacts have drawn considerable attention due to their high power conversion efficiency with a simple fabrication process. Titanium oxide (TiOx) is one of the most promising materials that can provide excellent surface passivation as well as carrier-selective transport. In this study, the authors fabricate the TiOx/SiOx/c-Si heterocontacts by atomic layer deposition (ALD) and investigate the effect of the forming gas annealing (FGA) on hydrogen content and surface morphology by utilizing nuclear reaction analysis (NRA) and atomic force microscope (AFM) measurements, respectively. The highest effective carrier lifetime (τeff) of 891 μs is realized for TiOx/SiOx/c-Si heterocontacts after FGA at 400 °C for 3 min, indicating that high surface passivation performance is obtained. NRA clarifies that the hydrogen content in the TiOx/SiOx/c-Si heterocontacts decreases with increasing FGA temperature and duration. With increasing FGA temperature and duration, also the surfaces of the TiOx/SiOx/c-Si heterocontacts are roughened, which means enhanced crystallization of the TiOx/SiOx/c-Si heterocontacts. From the NRA and AFM analyses, the authors conclude that there is a trade-off relationship between the hydrogen content in the TiOx/SiOx/c-Si heterocontacts and the crystallization of the TiOx layers.

Effect of hydrogen plasma treatment on the passivation performance of TiOx on crystalline silicon prepared by atomic layer deposition

The authors report on the effect of hydrogen plasma treatment (HPT) on the passivation performance of titanium oxide (TiOx) on crystalline silicon (c-Si) fabricated by atomic layer deposition. Recently, TiOx has gathered attention as an electron-selective contact material for silicon heterojunction (SHJ) solar cells due to its preferable work function and band lineup. Moreover, TiOx has excellent light transmission properties due to its large bandgap energy. In order to improve the power conversion efficiency of SHJ solar cells with TiOx, it is necessary to enhance the passivation performance. The effective carrier lifetime representing the passivation performance is enhanced by HPT and amounts to 407.2 μs after HPT at 200 °C for 1 min. This value is twice as high as after forming gas annealing, which is the standard method to enhance the passivation performance of TiOx/c-Si heterostructures. Nuclear reaction analysis clarifies that the hydrogen concentration (CH) at the TiOx/c-Si interface of the HPT-processed sample is higher than that of an as-deposited sample and that the peak position of the CH distribution is shifted closer to the TiOx/c-Si heterointerface after HPT. Moreover, thermal desorption spectroscopy shows that Si–H and Si–H2 hydrogen bonds increase with HPT. These results indicate that the atomic hydrogen produced by the hydrogen plasma diffuses toward the TiOx/c-Si interface and terminate the local dangling bonds, which is responsible for the improved passivation performance.

Alumina film deposited by spin-coating method for silicon wafer surface passivation

In the present work, alumina gel was developed for passivating silicon wafers. The alumina gel was prepared by sol–gel method with aluminum sec-butoxide as precursor. After coating, rapid thermal process (RTP) was conducted to activate the passivation effect. X-ray photoelectron spectroscopy and C–V curve were executed to evaluate film properties. The peak at 74.35 eV confirmed the formation of Al2O3. Meanwhile, a small peak at low binding energy decreased with the growth of annealing temperature, which was ascribed to the escape of hydrogen, leading to the decline of effective lifetime after 700 °C. The highest fixed charge (Qf) of − 1.16e12 cm−2 and superior interface defect density at mid gap (Dit) of 1.98e12 cm−2eV−1 were obtained at the annealing temperature of 700 °C, contributing to the highest effective minority carrier lifetime of 292 µs. The present work will be helpful to provide a more cost-effective technique for Al2O3 passivation.