n-MoS₂/p-Si Solar Cells with Al₂O₃ Passivation for Enhanced Photogeneration

Rehman, Atteq ur,Khan, Muhammad Farooq,Shehzad, Muhammad Arslan,Hussain, Sajjad,Bhopal, Muhammad Fahad,Lee, Sang Hee,Eom, Jonghwa,Seo, Yongho,Jung, Jongwan,Lee, Soo Hong American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.43

<P>Molybdenum disulfide (MoS2) has recently emerged as a promising candidate for fabricating ultrathin-film photovoltaic devices. These devices exhibit excellent photovoltaic performance, superior flexibility, and low production cost. Layered MoS2 deposited on p-Si establishes a built-in electric field at MoS2/Si interface that helps in photogenerated carrier separation for photovoltaic operation. We propose an Al2O3-based passivation at the MoS2 surface to improve the photovoltaic performance of bulklike MoS2/Si solar cells. Interestingly, it was observed that Al2O3 passivation enhances the built-in field by reduction of interface trap density at surface. Our device exhibits an improved power conversion efficiency (PCE) of 5.6%, which to our knowledge is the highest efficiency among all bulklike MoS2-based photovoltaic cells. The demonstrated results hold the promise for integration of bulklike MoS2 ails with Si-based electronics to develop highly efficient photovoltaic cells.</P>

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.

Silicon space solar cells: progression and radiation-resistance analysis

Rehman, Atteq ur,Lee, Sang Hee,Lee, Soo Hong 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.4

<P>In this paper, an overview of the solar cell technology based on silicon for applications in space is presented. First, the space environment and its effects on the basis of satellite orbits, such as geostationary earth orbit (GEO) and low earth orbit (LEO), are described. The space solar cell technology based on silicon-based materials, including thin-film silicon solar cells, for use in space was appraised. The evolution of the design for silicon solar cell for use in space, such as a backsurface field (BSF), selective doping, and both-side passivation, etc., is illustrated. This paper also describes the nature of radiation-induced defects and the models proposed for understanding the output power degradation in silicon space solar cells. The phenomenon of an anomalous increase in the short-circuit current (I-sc) in the fluence irradiation range from 2 x 10(16) cm(-2) to 5 x 10(16) cm(-2) is also described explicitly from the view point of the various presented models.</P>

Copper Conducting Electrode with Nickel as a Seed Layer for Selective Emitter Crystalline Silicon Solar Cells

Atteq ur Rehman,Eun Gu Shin,이수홍 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.5

In this research, we investigated selective emitter formation with a single-step photolithographyprocess having a metallization scheme composed of nickel/copper metal stacks. The nickel seedlayers were deposited by applying the electroless deposition process while copper was formed by lightinduced electro-plating arrangements as the main conducting electrode. The electroless depositionof nickel, along with a sintering process, was employed to create a diffusion barrier between copperand silicon. The nickel metal stack below the copper-conducting electrode also helped in loweringthe sheet resistance and improving the contact adhesion. The nickel used as a seed layer wassuccessfully demonstrated in the fabrication of a homogeneous 60/ emitter and selective emittercells. Lower series resistances of 0.165and 0.253were achieved for the selective emitter and thehomogeneous emitter cells, respectively. The best cell efficiency of 18.37% for the selective emittersolar cell was achieved, with average cell efficiencies of 18.17% and 17.3% for the selective emitterand the homogeneous emitter cells, respectively. An approximate efficiency increase of about 0.8%was recorded for the selective emitter solar cells.

Crystalline silicon thin-film solar cells on ceramic substrates

Rehman, Atteq Ur,Lee, Sang Hee,Lee, Soo Hong Springer-Verlag 2015 ELECTRONIC MATERIALS LETTERS Vol.11 No.2

Characterization of Nickel Silicide Formation by a Selective Electroless Plating Process for Crystalline Silicon Solar Cells

( Atteq Ur Rehman ),( Eun Gu Shin ),( Sang Hee Lee ),( Doo Won Lee ),( Soo Hong Lee ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.6

The nickel (Ni) electroless plating process is an encouraging method for selectively depositing Ni onto silicon (Si) wafers to form front electrodes of Si solar cells. Ni has the ability to block diffusion in copper (Cu), which is used for further thickening of the Ni contacts. The contact between Ni and Si can be optimized by an additional sintering step to form nickel-silicide (NiSix). This paper presents the characterization of NiSix according to bath conditions, deposition time, and sintering process. The selective electroless deposition of Ni was achieved by plating from an alkaline nickel chloride (NiCl2) bath with ammonia as the pH control and sodium hypophosphite as the reducing agent. Thin clusters of Ni were deposited on top of Si, which ensured the formation of uniform Ni seed layers with better surface coverage on both textured and non-textured Si surfaces. The dominant phase of NiSi that offered the lowest series resistance was confirmed by X-ray diffraction (XRD) analysis at sintering temperatures of 350 ºC and 400 ºC. Selective deposition of Cu over the Ni seed layer was achieved by light induced plating arrangements, and thin finger lines with widths up to 28.4 μm were realized. (Received July 1, 2015)

Development and prospects of surface passivation schemes for high-efficiency c-Si solar cells

ur Rehman, Atteq,Iqbal, Muhammad Zahir,Bhopal, Muhammad Fahad,Khan, Muhammad Farooq,Hussain, Farhan,Iqbal, Javed,Khan, Mahmood,Lee, Soo Hong Elsevier 2018 Solar energy Vol.166 No.-

<P><B>Abstract</B></P> <P>Photovoltaic (PV) electric power generation has the potential to account for a major portion of power generation in the global power market. Currently, the PV market is dominated by crystalline silicon (c-Si) solar cells which accounts for more than 80% of the share. Lower cost, optimized process parameters and improved PV cell efficiencies are required to reduce the overall cost per watt peak (W). In this regard, PV cell manufacturers are currently adopting thinner wafers, which tends to increase the surface recombination velocity (SRV). Excellent surface passivation at the front and rear of the PV cell becomes imperative for realizing superior efficienciy on c-Si substrates. In this article, our focus is to discuss the role of the surface passivation process for improving the PV cell efficiency. The fundamentals and strategies to improve the surface passivation for c-Si solar cells are discussed. Surface passivation schemes and materials with the ability to offer field effect passivation with dielectric charges (positive/negative) present in the passivation films were reviewed. Moreover, we discuss the use of a thin-dielectric passivation layer with a properly selected work function and band offsets for tunneling contacts, facilitating a higher efficiency potential. Finaly, the front/rear surface passivation schemes required for thinner wafers to maintain higher bulk lifetime and higher efficiencies for c-Si solar cells are presented.</P>

Investigations of the Boron Diffusion Process for n-type Mono-Crystalline Silicon Substrates and Ni/Cu Plated Solar Cell Fabrication

Lee, Sunyong,Rehman, Atteq ur,Shin, Eun Gu,Lee, Soo Hong Korea Photovoltaic Society 2014 Current Photovoltaic Research Vol.2 No.4

A boron doping process using a boron tri-bromide ($BBr_3$) as a boron source was applied to form a $p^+$ emitter layer on an n-type mono-crystalline CZ substrate. Nitrogen ($N_2$) gas as an additive of the diffusion process was varied in order to study the variations in sheet resistance and the uniformity of doped layer. The flow rate of $N_2$ gas flow was changed in the range 3 slm~10 slm. The sheet resistance uniformity however was found to be variable with the variation of the $N_2$ flow rate. The optimal flow rate for $N_2$ gas was found to be 4 slm, resulting in a sheet resistance value of $50{\Omega}/sq$ and having a uniformity of less than 10%. The process temperature was also varied in order to study its influence on the sheet resistance and minority carrier lifetimes. A higher lifetime value of $1727.72{\mu}s$ was achieved for the emitter having $51.74{\Omega}/sq$ sheet resistances. The thickness of the boron rich layer (BRL) was found to increase with the increase in the process temperature and a decrease in the sheet resistance was observed with the increase in the process temperature. Furthermore, a passivated emitter solar cell (PESC) type solar cell structure comprised of a boron doped emitter and phosphorus doped back surface field (BSF) having Ni/Cu contacts yielding 15.32% efficiency is fabricated.

Analysis of Ni/Cu Metallization to Investigate an Adhesive Front Contact for Crystalline-Silicon Solar Cells

이상희,이수홍,Atteq ur Rehman,신은구,이동원 한국광학회 2015 Current Optics and Photonics Vol.19 No.3

Developing a metallization that has low cost and high efficiency is essential in solar-cell industries,to replace expensive silver-based metallization. Ni/Cu two-step metallization is one way to reduce the costof solar cells, because the price of copper is about 100 times less than that of silver. Alkaline electrolessplating was used for depositing nickel seed layers on the front electrode area. Prior to the nickel depositionprocess, 2% HF solution was used to remove native oxide, which disturbs uniform nickel plating. In thesubsequent step, a nickel sintering process was carried out in N2 gas atmosphere; however, copper wasplated by light-induced plating (LIP). Plated nickel has different properties under different bath conditionsbecause nickel electroless plating is a completely chemical process. In this paper, plating bath conditionssuch as pH and temperature were varied, and the metal layer's structure was analyzed to investigate theadhesion of Ni/Cu metallization. Average adhesion values in the range of 0.2-0.49 N/mm were achievedfor samples with no nickel sintering process

Investigations of the Boron Diffusion Process for n-type Mono-Crystalline Silicon Substrates and Ni/Cu Plated Solar Cell Fabrication

Sunyong Lee,Atteq ur Rehman,Eun Gu Shin,Soo Hong Lee 한국태양광발전학회 2014 Current Photovoltaic Research Vol.2 No.4

A boron doping process using a boron tri-bromide (BBr₃) as a boron source was applied to form a p+emitter layer on an n-type mono-crystalline CZ substrate. Nitrogen (N₂) gas as an additive of the diffusion process was varied in order to study the variations in sheet resistance and the uniformity of doped layer. The flow rate of N2 gas flow was changed in the range 3 slm~10 slm. The sheet resistance uniformity however was found to be variable with the variation of the N2 flow rate. The optimal flow rate for N₂ gas was found to be 4 slm, resulting in a sheet resistance value of 50 Ω/sq and having a uniformity of less than 10%. The process temperature was also varied in order to study its influence on the sheet resistance and minority carrier lifetimes. A higher lifetime value of 1727.72㎲ was achieved for the emitter having 51.74 Ω/sq sheet resistances. The thickness of the boron rich layer (BRL) was found to increase with the increase in the process temperature and a decrease in the sheet resistance was observed with the increase in the process temperature. Furthermore, a passivated emitter solar cell (PESC) type solar cell structure comprised of a boron doped emitter and phosphorus doped back surface field (BSF) having Ni/Cu contacts yielding 15.32% efficiency is fabricated.