Production of Aluminum Oxide

 A Simple system to Produce an Aluminum Oxide- Passivated Tungsten Diselenide/ n- Type Si Heterojunction Solar Cell with High Power Conversion Efficiency 

Abstract

Transition essence dichalcogenide( TMDC) accoutrements are seductive campaigners for 2D solar cell bias thanks to their straightforward integration with colorful substrates and traditional semiconductor technologies, wide band gap ranges over the visible light diapason, and high immersion measure values. Although there are several former reports on the fabrication of 2D material- grounded solar cells, delicate and complex processes in the fabrication are largely needed to be modified for wider use in diurnal life operations. Photolithography, the most generally used manufacturing process for TMDC- grounded solar cells, is complicated. In this study, we demonstrate that the fabrication of 2D tungsten diselenide( WSe2) by espousing a wet transfer process with thermal release tape recording simplifies the manufacturing way for TMDC- grounded solar cell bias. This simplification not only reduces the product cost by banning several factors similar as transmittance, thermal expansion, face flatness, and continuity but also improves the yield. likewise, a evidence- of- conception demonstration of creating a WSe2 Si junction with an aluminum oxide( Al2O3) antireflective coating handed a power conversion effectiveness of6.39, which is a significant enhancement over that of a WSe2 Si solar cell without the antireflective coating subcaste(1.08).

1. Introduction

The earth’s temperature is  sluggishly  adding  owing to global warming caused by the enormous dependence of humans on fossil energies as energy sources. In the process of maintaining carbon dioxide( CO2) at a  fairly safe  position to avoid environmental catastrophe, indispensable energy sources that are clean, green,  dependable, and free from carbon are  largely desirable. largely abundant solar energy is the most  reliable and potent renewable energy option( 1 – 4), and making solar cells to harness it that are  largely effective and affordable is  crucial to  diving  the continuously  adding  energy demand around the globe. sweats are ongoing in the  exploration community to develop cheap photovoltaics with practicable power conversion  effectiveness( PCE)  situations. still, these  sweats are being hindered by  colorful limitations in the fabrication, selection, stability, and affordability of photovoltaic accoutrements ( 5, 6).   Graphene, a zero- band gap material, is  unable of electrically driven light emigration. On the other hand, transition essence dichalcogenides( TMDCs) have drawn  important attention for use in  colorful optoelectronic, 2D solar cell, energy conversion, and  storehouse  operations owing to their layered nature and tunable consistence-dependent band gap energy  situations( 7 – 11). Solar cells that are only a many layers comprising 2D TMDCs with van der Waals junctions have shown outstandingly high photocurrent  situations. In recent times, 2D MXenes have also drawn interest in the field of photovoltaics as electron transport subcaste for their distinctive  parcels  similar as metallic conductivity and tunable work function for  perfecting the device  effectiveness and stability( 12, 13). also, compared to being solar cells, they've comparatively advanced chemical stability and bear  lower material, leading to a cost reduction in their fabrication( 14).   Due to their band gap energy and consistence-dependent  geste 

            , 2D accoutrements   similar as molybdenum disulfide( MoS2) and tungsten diselenide( WSe2) have  lately gained noteworthy attention as accoutrements  for making solar cells. MoS2 and WSe2 monolayers have a direct band gap while their bulk forms can be used to produce  circular semiconductors( 1, 4, 15 – 18). Among the TMDCs for solar cells, tungsten diselenide( WSe2) is the most promising  seeker  substantially due to its bulk band gap energy of  eV. The Shockley- Queisser detailed balance limit provides the maximum photoconversion  effectiveness for a single absorber comprising WSe2. also, WSe2 possesses a high  immersion measure of 105 cm- 1 at 780 nm and high electron and hole carrier mobility(> 100 cm2/ V s)( 19, 20).   WSe2 has been used as an absorber in  interesting 2D solar cell  examinations( 21, 22). still, the bones

             with a sufficiently high PCE haven't yet been achieved and have failed to meet the theoretical PCE range of 20 – 27. therefore, it's  largely desirable to more effectively exploit TMDCs in solar cells, especially WSe2 considering its electronic  parcels, passivation effect,  continuity, and use as a counter electrode( 23 – 25). Al2O3 with a band gap of  83 eV is well known for its superior dielectric, thermal stability, and excellent adhesion to other accoutrements . Due to its capability to increase  natural  eventuality and reduce recombination, Al2O3 serves as an electron blocking subcaste and a passivating subcaste for silicon  shells. also, Al2O3 film helps in  dwindling the leakage current which restricts the  separating characteristics that impacts the  effectiveness of the device. Large  erected- in fields are produced as a result of lower reflection losses due to the Al2O3 subcaste and an increase in photons trapped inside the  reduction area.   In this study, we explored a WSe2/ n- type Si heterojunction solar cell and the effect of aluminum oxide( Al2O3) passivation on its PCE. A large area of WSe2 was grown via chemical vapor deposit( CVD) and simply wet transferred with thermal release tape recording( TRT) to produce a WSe2 film that's a many layers thick. In addition, we fabricated a WSe2/ n- type Si heterojunction solar cell with Au fritters as the top contact and Ti Pd/ Ag as the  nethermost contact. An Al2O3 antireflective and passivating subcaste was  carpeted on the device by using  infinitesimal subcaste deposit( ALD). The CVD- grown WSe2 was atomically thin. The photovoltaic performance of the WSe2/ n- type Si heterojunction solar cell with an Al2O3 passivating subcaste under air mass( AM)1.5 was  attained. Al2O3  face passivation, band alignment between WSe2 and n- type Si, and PCE  enhancement in the WSe2/ n- type Si- enabled heterojunction solar cell due to the Al2O3 passivating subcaste were also delved . The consistence of the  set Al2O3 interfacial subcaste is around 10 nm. The purpose of using 10 nm consistence is to ameliorate the trap  viscosity of deteriorated Al2O3/ WSe2 interface( 26). As reported in  former reports, the 10 nm consistence of Al2O3 will help in the  repression of the Coulomb scattering, thereby modifying the  dissipation of phonons. also, the growth of ALD is helpful in removing the  contaminations, and due to the difference in the dielectric constant of silicon and Al2O3,  thus passivation subcaste using Al2O3 significantly improves the solar cell device  effectiveness 

2. Experimental

2.1. Wafer- Scale Growth of WSe2 The growth of WSe2 was carried out in a 2- inch perpendicular cold- wall chamber. Tungsten hexacarbonyl( THC, W( CO) 6) and diethyl sulfide( DES,( C2H5) 2Se) as the W and Se precursors, independently, in the gassy phase were fitted into the chamber. We maintained THC used for growth at 0 °C, DES at-15 °C, and grew WSe2 in vapor phase form using Ar gas. Ar and H2 were also fitted into the chamber to deliver and reply with the W and Se precursors, independently. The optimized experimental conditions to produce WSe2 flicks were a total pressure of 50 Torr, a growth temperature of 600 °C, and a growth time of 130 min the dilution gas to acclimate the inflow rate was 50 sccm and 57 sccm, and the total quantum flowed to 60 sccm. The inflow rates of the precursors were 10 and 3 sccm for THC and DES, independently, which increased to 60 and 5 sccm by adding Ar and H2 gas, independently. . drawing Process of n- Type Si n- type,( 100)- acquainted bare polished native oxide( SiO2) was unravel with phosphorous with resistivity ranging from 1 to 10Ωcm. The junking of heavy remainders was achieved by drawing the Si substrates using warm( 55 °C) trichloroethylene( TCE), acetone, methanol, and deionized( DI) water. . Transferring the WSe2 Film onto an n- Type Si Substrate A 100 nm thick polymethyl methacrylate( PMMA) subcaste was deposited onto WSe2/ SiO2 samples via spin coating at 3000 rpm for 45s. After drying, it was immersed in acetone for 3 h to remove the PMMA and annealed in an Ar atmosphere at 350 °C for 4 h to remove the polymer remainders and pollutants. The frontal electrodes were made of essence grid cutlet bars, and the WSe2/ n- type Si with TRT was fixed at the edge to avoid the Schottky contact of the essence with Si. Although the essence grid bars were larger than the WSe2 film, the size of the device was acclimated by using TRT. The TRT was fluently removed by hotting
to 120 °C, and Cr( 10 nm)/ Au( 90 nm) was deposited on the front( emitter) side of the electrodes by using ane-beam evaporator at a base pressure of Torr and a deposit rate of ∼1.6 nm s- 1. subsequently, ane-beam evaporator was used to deposit Ti( 5 nm)/ Pd( 5 nm)/ Ag( 400 nm) on the aft side of the electrodes to insure low contact resistance. . Fabrication of the Al2O3 Antireflective Layer A traveling surge type Lucida D100 system( NCD Tech,Inc., Korea) was used to deposit an antireflective Al2O3 subcaste on the Si substrate at 170 °C. Trimethylaluminum( TMA; EzchemCo.,Ltd., Korea) was used as the Al source and DI water as the O source. Exceptionally pure N2 carrier gas(99.999) at a inflow rate of 20 sccm was used to carry the separate sources into the response chamber. The antireflective Al2O3 subcaste was grown by using the following ALD precursor palpitation and purge procedure TMA palpitation(0.1 s) → N2 purge( 8 s) → H2O palpitation(0.1 s) → N2 purge( 8 s). . Characterization Tools and Photovoltaic measures The electronic structure of WSe2 was determined by using the Raman spectroscopy( Renishaw in- Via,514.5 nm wavelength). With a spot size of around0.8 μm, a modest input power of 1 mW was employed to help any ray- related device damage. measures were taken at several locales, and the average findings were calculated to insure the thickness and correctness of the data deduced from each sample. The consistence of the WSe2 subcaste was examined via infinitesimal force microscopy( AFM; MultiMode 8, Bruker, USA). The WSe2 essential composition was determined by usingX-ray photoelectron spectroscopy( XPS; K- nascence, Thermo UK) with an Al K monochromator(1486.6 eV) and a variable spot size( 30 – 400 μm). Across-sectional view of the WSe2 film face was vindicated by using high- resolution transmission electron microscopy( TEM; JEOL, JEM- F200). A UV- vis-near- IR spectrophotometer was exploited to capture optic reflectance gamuts in the 200 – 900 nm region( V- 750, JASCO). The photovoltaic performance of the device was measured by using a source cadence in a solar simulator( 1 sun power Newport)( Keithley 2400). The system was calibrated with test samples before taking experimental measures.

3. Results and Discussion

 Numbers 1( a) and 1( b) show inflow maps of the conventional photolithography- grounded and new wet transfer with TRT- grounded  styles for fabricating a p- n heterojunction solar cell, independently, in which it can be seen that the new process is  important simpler. Au and Al2O3 are two of the most  pivotal parameters in the device. Al2O3 was used as an antireflective subcaste of van der Waals( VDW) heterojunction- grounded p- n junction solar cell formed by the p- type WSe2 and n- type silicon contact. thus, Al2O3 wasn't deposited on top of Au contact as shown in Figure 2( a). It's critically essential that the depleted region of the VDW heterojunction device can separate the photoinduced charge carriers  fleetly. The charges have been separated due to the creation of a  erected- in field and  contemporaneously collected at the top and  nethermost electrodes. The effective separation of photogenerated electron- hole  dyads will  produce large  erected- in fields which are  largely desirable to  induce large photocurrents;  thus, it improves the  effectiveness of a solar cell. still, there are certain  rudiments that degrade the performance  similar as  inescapably  converting interface  blights causing high recombination rate and lower  erected- in fields. Another important parameter is the illumination of solar simulator light which creates photons that must be absorbed in the  reduction region rather than in the charge-neutral region in order to reduce the recombination of photogenerated electron- hole  dyads( 30). thus, we've created two types of structures with and without Al2O3. In this case, without Al2O3, smaller photons are trapped within the  reduction region and have a lower continuance that redounded in large leakage currents and lower  effectiveness. still, with Al2O3, the reflection losses are reduced, and more photons are trapped within the  reduction region, creating large  erected- in fields. McVay etal.( 3) produced a WSe2 solar cell device with a PCE of0.96 by using a photolithography  system. In the present  exploration, we can confirm that removing the photoresist step not only simplifies the fabrication process but also solves the problem of residual chemicals,etc., and has a good effect on  perfecting the performance of the device( 31, 32). The unique approach was  espoused to fabricate solar cell  bias without using the complicated lithography process and still producing a large active area that's essential from an artificial perspective. Figure 1( c) presents a schematic of the new simple fabrication process of a WSe2 Si heterojunction by exploiting the wet transfer  system. 

4. Conclusions

We successfully demonstrated the fabrication of a 2D WSe2/ n- type Si heterojunction solar cell device involving a wet transfer process with TRT that's far simpler than the complicated lithography procedure. The  consummation of a WSe2/ n- type Si heterojunction solar cell with Au fritters as the  frontal contact and Ti Pd/ Ag as the  nethermost contact was achieved. The multilayered WSe2 film  handed an effective photovoltaic performance. likewise,  face doping and  face passivation with a coating of an Al2O3 passivating subcaste via ALD helped to enhance the PCE of the WSe2/ n- type Si solar cell from1.08 to6.39, which highlights the significance of  face passivation as well as an antireflection coating in TMDC- grounded solar cells. This work paves the way to realize TMDC- grounded solar cells with high PCEs by applying a facile cost-effective TRT approach as well as  face passivation through Al2O3. This strategy could be  employed for other TMDCs in solar cells.