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Mallem, Kumar,Kim, Yong Jun,Hussain, Shahzada Qamar,Dutta, Subhajit,Le, Anh Huy Tuan,Ju, Minkyu,Park, Jinjoo,Cho, Young Hyun,Kim, Youngkuk,Cho, Eun-Chel,Yi, Junsin Elsevier 2019 Materials research bulletin Vol.110 No.-
<P><B>Abstract</B></P> <P>Transition metal oxides (TMO) are extensively applied as a surface passivation and carrier-selective contact layer through replacing boron/phosphorus doped emitter layers in silicon heterojunction (SHJ) solar cell applications. In this regard, molybdenum oxide (MoO<SUB>3</SUB>) has drawn a significant attention as a hole extraction layer owing properties such as wide bandgap (∼3 eV), high work function (>6 eV) and low temperature deposition. Thus, we fabricated SHJ solar cells with a dopant-free MoO<SUB>x</SUB> applied at the front surface contact layer. Thermally evaporated MoO<SUB>x</SUB> films were exhibited optical characteristics such as high transmittance, high bandgap and low absorption coefficient as compared to a-Si:H(p) and μc-SiO<SUB>x</SUB>:H (p) layers. X-ray photoelectron spectroscopy (XPS) analysis confirmed the stoichiometric and oxidation deficiency states of the of the MoO<SUB>x</SUB> layers. Whereas, MoO<SUB>x</SUB> films undergoing long-term air exposure showed an increase in Mo<SUP>5+</SUP> cations due to the increased oxygen vacancy. The fabricated MoO<SUB>x</SUB>/c-Si heterojunction solar cells achieved a significant power conversion efficiency (η) of 20%, best open circuit voltage (V<SUB>oc</SUB>) of 695 mV, high short circuit current density (J<SUB>sc</SUB>) of 38.88 mA/cm<SUP>2</SUP> and a fill factor (FF) of 74.0%. These results implying that MoO<SUB>x</SUB> is as an excellent dopant-free material for alternate p-doped a-Si:H emitter layers in SHJ solar cell applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> MoO<SUB>x</SUB> layer was used to fabricate high efficiency of Si heterojunction solar cells. </LI> <LI> MoO<SUB>x</SUB> layers exhibited high transmittance, bandgap and low absorption coefficient. </LI> <LI> XPS analysis confirmed the stoichiometric analysis of MoO<SUB>x</SUB> films. </LI> <LI> Thickness and ambient annealing effect on the MoO<SUB>x</SUB>/Si was strictly investigated. </LI> <LI> 20.0% improved cell efficiency was achieved for MoO<SUB>x</SUB>/Si heterojunction solar cells. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Siva Pratap Reddy Mallem,Peddathimmula Puneetha,Kalupudi Subramanyam,Varra Rajagopal Reddy,이동연,김영래,안성진,박귀일 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.4
Cubic-structured europium (Eu) doped zinc sulfide (ZnS) nanoparticles (NPs) were prepared via refluxing at 150 °C. Absolute structural studies showed that Eu+ ions were successfully substituted into the ZnS host lattice and changed the original structure of the host. As-fabricated ZnS:Eu NPs exhibited typical red emission due to the transition of the Eu dopant in the 5d0-7f1, 5d0-7f2, 5d0-7f3, and 5d0-7f4 energy levels of the 4f orbital of the dopant. The typical diamagnetic ZnS could be converted to tunable paramagnetic as a function of Eu-doping content. These NPs were quantified for hydrogen evolution through water splitting by artificial solar spectrum. Eu doping can drastically enhance the hydrogen (H2) evolution capability of ZnS, which is higher than that of bare ZnS NPs. The causes behind these engrossing results will be revealed. These interesting properties may find applications in optoelectronics, spintronics, and H2 evolution.
Gate Architecture Effects on the Gate Leakage Characteristics of GaN Wrap‑gate Nanowire Transistors
Siva Pratap Reddy Mallem,Ki‑Sik Im,Terirama Thingujam,Jung‑Hee Lee,Raphael Caulmilone,Sorin Cristoloveanu 대한금속·재료학회 2020 ELECTRONIC MATERIALS LETTERS Vol.16 No.5
Gate leakage current in lateral GaN wrap-gate nanowire transistors (WG-NWT) was investigated using current density–voltage (Jg–Vg) characteristics at room temperature. We found that the gate leakage current is strongly dependent on thetop corner angle of the gate architecture. This leakage current was characterized by considering hopping (Poole–Frenkelemission) and trap-assisted thermionic emission mechanisms. Despite its smaller gate area, the gate leakage current of thelateral GaN WG-NWT without a 2DEG channel was higher than that of the device with a 2DEG channel for all applied gatebiases. The reason for this is that the lateral GaN WG-NWT without 2DEG channel has a triangular cross-section with asharp top corner angle resulting in a strong electric field due to geometrical field enhancement.
Strain-controlled Flexible DNA-curcumin on PET Substrate
Siva Pratap Reddy Mallem(말렘 시바 프래탑 래디),Jung-Hee Lee(이정희) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4
High-performance strain-modulated flexible sensors are significant modules of the systems for human motion detection, electronic skin, human-machine interaction, soft robotics, etc., which are intended as important technologies for applications in future human personal healthcare monitoring and artificial intelligence. Resistive switching, which use modification in resistance measurement, is considered as one of the prospective candidate for the future generation key technology. We introduce a simple technique to fabricate a flexible resistive-type strain sensor composted of DNA-curcumin composite and graphene on polyethylene terephthalate (PET) substrate. Double helical DNA has unique attributes including its high thermal stability, high negative charge density and strong resistance to both bending and twisting. Particularly, flexible DNA-curcumin/graphene on PET substrate displays piezo-resistive characteristics, is likely a good candidate for fabricating resistance-based strain sensors.
Ju, Minkyu,Mallem, Kumar,Dutta, Subhajit,Balaji, Nagarajan,Oh, Donghyun,Cho, Eun-Chel,Cho, Young Hyun,Kim, Youngkuk,Yi, Junsin Elsevier 2018 Materials science in semiconductor processing Vol.85 No.-
<P><B>Abstract</B></P> <P>Front side textured random pyramids are widely utilized in major industries for the performance enhancement of crystalline silicon (c-Si) solar cells. Random pyramids not only reduce the surface reflectance but also improve the light trapping effect. Therefore, it is necessary to understand the pyramid height affecting the cell performance, further improving cell efficiency. In this work, we present an experimental study to investigate the influence of pyramids size on the contact shading loss mechanism of silver (Ag) screen-printed p-type c-Si solar cells. Three alkaline texture solutions with sodium silicate additives were optimized to develop the small pyramid (0.5–2.0 µm) size, middle pyramid (5.0–9.0 µm) size and large pyramid (10–15 µm) size on the c-Si surface, respectively. It was noticed that screen-printed finger width strongly depends on pyramid size. Even though, same mesh patterns and screen printing conditions resulted in 20 µm widening of metal finger width on the large pyramids as compared to the small pyramids. This was attributed to the increase in the size of cell surface pyramids that not only varied the gap between the screen mesh and cell surface while screen-printing but also hindered the contraction of metal electrodes during the firing process. The c-Si solar cells with large pyramids suffered from an extra shading loss during fabrication, thus, led to the reduction of the short circuit current density (~0.7 mA/cm<SUP>2</SUP>) resulting in lower efficiency (~17.72%) as compared to efficiency (~18.60%) of small pyramid based cells.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Random textured pyramid size effect on the Ag-printed Si solar cells is investigated. </LI> <LI> Anisotropic etching and pyramid size was controlled with NaOH-IPA additive of Na<SUB>2</SUB>SiO<SUB>3</SUB>. </LI> <LI> Improved performance of small pyramid archived of ~0.7 mA/cm<SUP>2</SUP> higher than large pyramid. </LI> <LI> Textured pyramid height and figure contact roughness was confirmed by SEM images. </LI> <LI> Contact widening and shading loss analysis of small to large pyramid cells are studied. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
High-efficiency Crystalline Silicon Solar Cells: A Review
Sanchari Chowdhury,Mallem Kumar,DUTTA SUBHAJIT,박진수,김재민,김세현,주민규,김영국,조영현,조은철,이준신 한국신·재생에너지학회 2019 신재생에너지 Vol.15 No.3
Solar energy is a clean renewable energy resource that can be converted to electricity with photovoltaic (PV) technology without environmental damage. Solar energy can be transformed to electricity using a range of technologies, but crystalline silicon (c-Si)-based PV technology dominates in the PV market due to the high efficiency, long-term stability, reliability, and second most abundant (27%) material. Recently, c-Si solar cells achieved an outstanding efficiency of 26.7% through silicon heterojunction technology combined with an interdigitated back contact structure. Most industries and researchers are attempting to improve the efficiency further to reach the silicon limit. The dominant position of crystalline silicon solar cell in large-area electricity production and industrialization motivated us to write this review paper. This review paper covers the key factors that affect the efficiency, such as structure, process optimization, cost reduction strategies. In addition, some promising cell structures, such as Passivated Emitter Rear Contact (PERC) solar cell, Interdigitated Back Contact (IBC) solar cell, Heterojunction Intrinsic Thin Layer (HIT) solar cell, and Heterojunction Back Contact (HBC) solar cell, and their efficiencies are reported. Overall, this study provides a detailed idea to the new photovoltaic researchers regarding the solar cell structure, their efficiencies, and future potential of solar cells.