Selective nickel/silver front metallization for graphene/silicon solar cells

Bhopal, Muhammad Fahad,Lee, Doo won,Lee, Sang Hee,Lee, Ah Reum,Kim, Han Jun,Lee, Soo Hong North-Holland 2019 Materials letters Vol.234 No.-

<P><B>Abstract</B></P> <P>In this work we studied front electrodes of nickel/silver (Ni/Ag) deposited on Gr/Si solar cell structure using field induced plating. These electrodes also be used as a front electrode on 2D graphene-based devices at very low cost and temperature (< 70 °C). Adhesion between the nickel and graphene was controlled by varying the solution temperature between 50 °C and 70 °C, followed by Ag plating at room temperature. It was observed that contact resistivity improved between plated electrodes and graphene, helpful in improving the <I>F.F</I> of the device from 49% to 60.1%. Efficiency was enhanced from 4.3% to 5.01%.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Field induced platting process was applied for Ag/Ni deposition on graphene/silicon cell structure. </LI> <LI> Ni/Gr interface helps to reduce the contact resistance. </LI> <LI> Reduction in contact resistance improved the <I>F.F</I> of Gr/Si solar cell. </LI> <LI> Efficiency improved from 4.3% to 5.01% having <I>F.F</I> 49.1% and 60.1%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Past and future of graphene/silicon heterojunction solar cells: a review

Bhopal, Muhammad Fahad,Lee, Doo Won,Rehman, Atteq ur,Lee, Soo Hong Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.41

<▼1><P>Graphene/silicon (Gr/Si) Schottky junction solar cells represent an alternative low-cost, easy fabrication structure in photovoltaic devices.</P></▼1><▼2><P>Graphene/silicon (Gr/Si) Schottky junction solar cells represent an alternative low-cost, easy fabrication structure in photovoltaic devices. After graphene's emergence in 2004, the first Gr/Si solar cell was fabricated in 2010, and was able to achieve upto 15% efficiency in less than a decade. This breakthrough in cell efficiency was realized by the fact that Gr has tremendous electrical and optical properties for photovoltaic applications. In this review, we highlight some of the recent progress in Gr/Si heterojunction solar cells. The growth processes of 2D graphene using the CVD process are discussed in detail. Afterwards, the key parameters that help to enhance the power conversion efficiency (PCE) of solar cells are considered. The interface of Gr/Si and the effects of chemical doping on the cell parameters were studied. Lastly, the challenges and limitations along with the future developments for Gr/Si solar cells are discussed in detail.</P></▼2>

High-ĸ dielectric oxide as an interfacial layer with enhanced photo-generation for Gr/Si solar cells

Bhopal, Muhammad Fahad,Akbar, Kamran,Rehman, Malik Abdul,Lee, Doo won,Rehman, Atteq ur,Seo, Yongho,Chun, Seung-Hyun,Lee, Soo Hong Elsevier 2017 Carbon Vol.125 No.-

<P>In recent years, graphene (Gr) based solar cells have attracted extensive interest because of their ability to produce low cost and highly efficient solar cells. Conventional Gr/Si Schottky junction based solar cells are mostly fabricated by transfer of graphene on silicon substrate. In current work the direct growth of graphene by using the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique was demonstrated to make fabrication more practical on a large scale. Firstly Gr/Si Schottky junction based solar cells were fabricated, and by optimizing the growth process, power conversion efficiency (PCE) of about 3.5% was achieved. Additionally, we demonstrated a metal insulator semiconductor (MIS) structure by introducing hafnium oxide (HfO2), and an enriched efficiency of 6.68% was reached. Furthermore, the chemical doping of Gr grown on top of HfO2 passivated Si was done and the efficiency was further enhanced by 8.5%. This study also suggests that the Voc of the Gr/HfO2/Si solar cells strongly depends on the thickness of the HfO2 interfacial layer. These solar cells proved reliable as their efficiency was still consistent even after four months. The current study envisions the use of graphene based solar cells for commercial application. (C) 2017 Elsevier Ltd. All rights reserved.</P>

C-Si thin-films on carbon-related substrates: Deposition and photovoltaic cells

Bhopal, Muhammad Fahad,Rehman, Atteq ur,Lee, Doo won,Lee, Soo Hong Korean Physical Society 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.5

Influence of annealing temperature on structural properties of ITO thin-films on graphite substrate

Bhopal, M.F.,Lee, D.w.,Rehman, A.u.,Lee, S.H. Pergamon Press [etc.] 2016 Vacuum Vol.133 No.-

<P>In various industrial applications including thin-film solar cells indium tin oxide (ITO) is widely used. In this research work highly electrically conductive Tin-doped indium oxide (ITO) was deposited on graphite substrate using e-beam evaporator at substrate temperature 300 degrees C and 400 degrees C. Thermal treatment of the deposited ITO thin film was further done with the temperature values up to 900 degrees C. ITO nanostructures were found to be grown at 400 degrees C with diameters of 30-35 nm and remained stable even at 800 degrees C. At 900 degrees C, the ITO characteristics were observed to change. The In and Sn concentrations were decreased, while carbon (C) and oxygen (02) were found to be increased at 900 C. The increase in 02 was observed to be 54% while the concentration of C increased from 15% to 45%. Optical and FE-SEM characterization were done to study the morphology and surface roughness of ITO thin-films. TEM and XRD was used to study the crystallinity of these ITO nanostructures. Similarly, X-Ray photoelectron spectroscopy (XPS) was used to measure the components and the chemical state. Depth profiling was measured using secondary-ion-mass-spectroscopy (SIMS) of these thin films on graphite substrate at different annealed temperatures upto 900 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Poly-Crystalline Thin-Film by Aluminum Induced Crystallization on Aluminum Nitride Substrate

Muhammad Fahad Bhopal,이두원,이수홍 대한금속·재료학회 2016 ELECTRONIC MATERIALS LETTERS Vol.12 No.5

Thin-film polycrystalline silicon (pc-Si) on foreign (non-silicon)substrates has been researched by various research groups for theproduction of photovoltaic cells. High quality pc-Si depositionon foreign substrates with superior optical properties isconsidered to be the main hurdle in cell fabrication. Metalinduced crystallization (MIC) is one of the renowned techniquesused to produce this quality of material. In the current study, analuminum induced crystallization (AIC) method was adopted toproduce pc-Si thin-film on aluminum nitride (AlN) substrate by aseed layer approach. Aluminum and a-Si layer were depositedusing an e-beam evaporator. Various annealing conditions wereused in order to investigate the AIC grown pc-Si seed layers forprocess optimization. The effect of thermal annealing on grainsize, defects preferentially crystallographic orientation of thegrains were analyzed. Surface morphology was studied using anoptical microscope. Poly-silicon film with a crystallinity fractionbetween 95-100% and an FWHM between 5-6 cm−1 is achievable at low temperatures and for short time intervals. A grainsize of about 10 micron can be obtained at a low deposition rate on an AIN substrate. Similarly, Focused ion beam (FIB) alsoshowed that at 425 °C sample B and at 400 °C sample A were fully crystallized. The crystalline quality of pc-Si wasevaluated using μ-Raman spectroscopy as a function of annealed conditions and Grazing incidence X-ray diffraction(GIXRD) was used to determine the phase direction of the pc-Si layer. The current study implicates that a poly-silicon layerwith good crystallographic orientation and crystallinity fraction is achievable on AIN substrate at low temperatures and shorttime frames.

A Study of Silicon Crystallization Dependence upon Silicon Thickness in Aluminum-induced Crystallization Process

Lee, Doo Won,Bhopal, Muhammad Fahad,Lee, Soo Hong The Korean Institute of Metals and Materials 2018 대한금속·재료학회지 Vol.56 No.5

Review of advanced hydrogen passivation for high efficient crystalline silicon solar cells

Lee, Sang Hee,Bhopal, Muhammad Fahad,Lee, Doo Won,Lee, Soo Hong Elsevier 2018 Materials science in semiconductor processing Vol.79 No.-

<P>Hydrogen passivation, such as forming gas annealing and alneal (aluminum anneal) process, has been investigated for high efficient crystalline silicon solar cell structures, because the hydrogen atoms can reduce the surface recombination velocity. However, hydrogen could not diffuse deeply to passivate various defects within the silicon bulk. Further investigations into the properties of hydrogen in the silicon lead to the control of hydrogen atoms' charge states for their high diffusivity and reactivity. Also, research of the hydrogenated amorphous silicon nitride (a-SiNx:H) as a hydrogen source induced an 'advanced hydrogen passivation'. This paper provides a review of advanced hydrogen passivation applied on p-type, n-type and upgraded metallurgical grade crystalline silicon solar cells, respectively. Especially, the regeneration of boron-oxygen related defects, which cause carrier induced degradation, will be closely discussed since most of industrial solar cells are fabricated by boron-doped p-type silicon wafer. Moreover, laser-induced hydrogen passivation, which can locally recover defective area on the solar cells, will be addressed. In the conclusion, proper conditions of advanced hydrogen passivation for the successful improvement of minority carrier lifetime will be summarized.</P>

Aluminum Induced Crystallization of Amorphous Silicon Dependent on Annealing Conditions with Graphite Plate

이두원,Muhammad Fahad Bhopal,이수홍 대한금속·재료학회 2016 ELECTRONIC MATERIALS LETTERS Vol.12 No.1

Aluminum induced crystallization (AIC) of amorphous silicon wasstudied for thin-film solar cell. The AIC have been usually researchedon glass substrate which has smooth surface. However, in this paper, thegraphite plate was used as a substrate for using thin-film solar cellwhich has 1μm roughness. The growth silicon layer characteristic couldbe relatively different with that using glass substrate by the surfaceroughness. Therefore, the properties of crystallized silicon layer werestudied for grain size analysis with variation in temperature and timeduring the AIC annealing process. The crystalline fraction andcrystallinity was analyzed by Optical microscope, X-ray diffraction(XRD), and Raman spectrometer measurement methods. Additionally,the grain size was also relatively analyzed with FWHM results. As aresult of measurements, crystalline fraction of grown silicon wasincreased with the increasing of temperature and time. The maximumcrystalline fraction of grown silicon was 92.85% for 2400 minutes ofannealing duration at 500°C.

Ni/Cu/Ag Plated Contacts: A Study of Resistivity and Contact Adhesion for Crystalline-Si Solar Cells

Atteq ur Rehman,이상희,Muhammad Fahad Bhopal,이수홍 대한금속·재료학회 2016 ELECTRONIC MATERIALS LETTERS Vol.12 No.4

Ni/Cu/Ag plated contacts were examined as an alternate to Ag screenprinted contacts for silicon (Si) solar cell metallization. To realize areliable contact for industrial applications, the contact resistance and itsadhesion to Si substrates were evaluated. Si surface roughness by picosecond(ps) laser ablation of silicon-nitride (SiNx) antireflection coating(ARC) was done in order to prepare the patterns. The sintering processafter Ni/Cu/Ag full metallization in the form of the post-annealingprocess was applied to investigate the contact resistivity and adhesion. Avery low contact resistivity of approximately 0.5 mΩcm2 has beenachieved with measurements made by the transfer length method(TLM). Thin finger lines of about 26 μm wide and a line resistance of0.51 Ω/cm have been realized by plating technology. Improved contactadhesion by combining the ps-laser-ablation and post-annealing processhas been achieved. We have shown the peel-off strengths >1 N/mm witha higher average adhesion of 1.9 N/mm. Our pull-tab adhesion testsdemonstrate excellent strength well above the wafer breakage force.