Development of p-Type Nano Crystalline Si Film for Electrical Contact Layer with the Front Electrode of Amorphous Silicon Oxide Type Solar Cell

Kim, Sangho,Iftiquar, S. M.,Park, Jinjoo,Pham, Duy Phong,Shin, Chonghoon,Yi, Junsin American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.10

<P>In a thin film solar cell the doped p-type and n-type layers provide electric field that helps to separate the photo generated electron-hole pairs from the active layer. In order to achieve a better electrical transport of holes from the p-layer to the transparent conducting oxide electrode (TCO), the TCO/p interface was improved. We used a p-type double layer, consisting of high conductivity p-type nano crystalline silicon (p-nc-Si:H) and wide band gap hydrogenated amorphous silicon oxide (p-a-SiO:H), where the TCO/p-nc-Si:H was expected to give better electrical contact. As a result, an improved cell characteristics was observed with efficiency of 6.25%, with 900 mV open circuit voltage, 11 mA/cm(2) short circuit current density, 63.3% fill factor. The optimized p-nc-Si: H layer had electrical conductivity of 1.1 S/cm, activation energy of 41 meV and optical energy band gap of 2.04 eV, that was prepared in a radio frequency plasma enhanced chemical vapor deposition with high hydrogen dilution. One of the primary reasons for such an improvement is thought to be an improved electronic band structure at the TCO/p interface and efficient hole collection.</P>

Investigation of p-type nanocrystalline silicon oxide thin film prepared at various growth temperatures

Kim, Sangho,Iftiquar, S.M.,Shin, Chonghoon,Park, Jinjoo,Yi, Junsin Elsevier 2019 Materials chemistry and physics Vol.229 No.-

<P><B>Abstract</B></P> <P>Substrate temperature has an important role on the characteristic properties of a plasma deposited thin film silicon. In a heterojuction (HJ) solar cell, the higher deposition temperature initiates unwanted thermal diffusion of atom from one layer to another, thereby degrading device characteristics. Hence, we investigated the effect of substrate temperatures (<I>T</I> <SUB> <I>s</I> </SUB>) on p-type material and HJ device characteristics. We prepared p-type nanocrystalline silicon oxide (p-nc-SiO:H) layer at different <I>T</I> <SUB> <I>s,</I> </SUB> varying from 170 °C to 80 °C and observed that its opto-electronic properties improve at a lower <I>T</I> <SUB> <I>s</I> </SUB>. These p-nc-SiO:H were used in HJ solar cell as emitter and we found that the film prepared at 80 °C gives the best result. This emitter layer shows wide optical gap (2.32 eV), high electrical conductivity (3.5 S/cm) and high crystallinity (44%). In the rear emitter HJ solar cells, an improvement in fill factor from 72.2% to 74.5%, open circuit voltage from 708 mV to 718 mV and power conversion efficiency (PCE) from 19.3% to 20.1% was observed when the emitter of the cells was prepared at 170 °C–80 °C.</P> <P><B>Highlights</B></P> <P> <UL> <LI> P-type nano-crystalline silicon oxide layer was grown at a low temperature. </LI> <LI> These films show wider optical gap and high electrical conductivity. </LI> <LI> Crystalline volume fraction was high at 80 °C deposition temperature. </LI> <LI> Rear emitter solar cell shows better characteristics with this layer. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Bias–stress-induced threshold voltage shift dependence of negative charge trapping in the amorphous indium tin zinc oxide thin-film transistors

Nguyen, Cam Phu Thi,Trinh, Thanh Thuy,Dao, Vinh Ai,Raja, Jayapal,Jang, Kyungsoo,Le, Tuan Anh Huy,Iftiquar, S M,Yi, Junsin Institute of Physics 2013 Semiconductor science and technology Vol.28 No.10

<P>Indium tin zinc oxide (ITZO)-based thin-film transistors (TFTs) were fabricated by dc magnetron sputtering in Ar + O<SUB>2</SUB> reactive gas, at room temperature. We present the effect of post-deposition annealing of ITZO thin films on the oxygen vacancies and on the characteristics of TFT devices. When the annealing temperature was increased from room temperature to 350 °C, the resistivity of ITZO film increased from 2.05 × 10<SUP>1</SUP> to 2.60 × 10<SUP>3</SUP> Ω cm and the interface trap density (<I>N</I><SUB>t</SUB>) of the TFTs reduced from 3.18 × 10<SUP>13</SUP> to 4.83 × 10<SUP>11</SUP> cm<SUP>−2</SUP>. The TFT with the ITZO film which was annealed at 350 °C showed a very small shift in turn-on voltage, even after applying positive bias stress of +12 V for 10<SUP>4</SUP> s. The current–voltage characteristics of 350 °C annealing temperature sample indicated that these TFTs were in an enhanced mode of transistor operation with a high on-to-off current ratio of ∼1.26 × 10<SUP>6</SUP>, high field-effect mobility of 14.17 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, and low subthreshold slope of 1.23 V/dec. The trapping time reduced from 3720 to 1546 s as the annealing temperature increased from room temperature to 350 °C. These results suggest that thermal annealing played an important role in reducing defects as well as improvement in stability of the TFTs.</P>

Low Reverse Saturation Current Density of Amorphous Silicon Solar Cell Due to Reduced Thickness of Active Layer

S M Iftiquar,Junsin Yi 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.4

One of the most important characteristic curves of a solar cell is its current density-voltage (J-V) curve under AM1.5G insolation. Solar cell can be considered as a semiconductor diode, so a diode equivalent model was used to estimate its parameters from the J-V curve by numerical simulation. Active layer plays an important role in operation of a solar cell. We investigated the effect thicknesses and defect densities (Nd) of the active layer on the J-V curve. When the active layer thickness was varied (for Nd = 8×10<SUP>17</SUP> cm<SUP>-3</SUP>) from 800 nm to 100 nm, the reverse saturation current density (Jo) changed from 3.56×10<SUP>-5 </SUP>A/cm2 to 9.62×10<SUP>-11</SUP> A/cm<SUP>2</SUP> and its ideality factor (n) changed from 5.28 to 2.02. For a reduced defect density (Nd = 4×10<SUP>15</SUP> cm<SUP>-3</SUP>), the n remained within 1.45≤n≤1.92 for the same thickness range. A small increase in shunt resistance and almost no change in series resistance were observed in these cells. The low reverse saturation current density (Jo = 9.62×10<SUP>-11</SUP> A/cm<SUP>2</SUP>) and diode ideality factor (n = 2.02 or 1.45) were observed for amorphous silicon based solar cell with 100 nm thick active layer.

Theoretical investigation of silicon thin film solar cell for improving short and long wavelength response

Iftiquar S.M.,Yi Junsin 한국물리학회 2023 Current Applied Physics Vol.50 No.-

Theoretical investigation or numerical simulation of performance of a solar cell can provide useful information to maximize power conversion efficiency. In that respect we carried out a set of numerical simulation using AFORS-HET simulation program. Separately the optical absorption of the individual layers of thin film solar cell was analyzed. Current-voltage characteristic curve of a reference cell (Cell-A) was used as the starting device. The power conversion efficiency (PCE) of the reference device was 8.85% with short circuit current density (Jsc) of 15.43 mA/cm2 and fill factor (FF) of 68.3%. After suitable optimization the PCE of this device (Cell-B2) improves to 11.59% (Jsc and FF became 13.0 mA/cm2 and 87% respectively). The results show that the effective optical absorption in the active layer can be improved significantly by optimizing the device structure. The short wavelength response can be improved by reducing the parasitic optical absorption of the doped window layer, while the long wavelength response improves by raising effective absorption length of the active layer. Furthermore, optimum thickness of the active layer, for the highest possible PCE, is found to be dependent upon its defect density.

Theoretical investigation of transparent front surface field layer on the performance of heterojunction silicon solar cell

Iftiquar, S.M.,Park, Hyeongsik,Kim, Sangho,Yi, Junsin Elsevier 2020 Solar Energy Materials and Solar Cells Vol.204 No.-

<P><B>Abstract</B></P> <P>In order to couple more light in absorber layer of a silicon heterojunction (SHJ) solar cell, higher optical transparency of the front layer is desirable. In that respect we investigated indium tin oxide (ITO) as a front surface field (FSF) layer in a rear emitter SHJ solar cell. We used numerical simulation starting from an experimentally obtained real solar cell. In the experimental cell the n-type nanocrystalline silicon (n-ncSi:H) was used as the FSF, where the power conversion efficiency (PCE) of the reference cell was 21.84%. Our investigation shows that if 20 nm thick ITO is used as the FSF, the PCE of the device can be 25.67%, while with an 80 nm thick ITO as FSF, the PCE can be 23.8%. This improvement in the device efficiency primarily comes with the increase in current density in the solar cell due to an increased intensity of light in the absorber layer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Silicon heterojunction solar cells were investigated theoretically. </LI> <LI> Reference experimental cell is of rear emitter structure. </LI> <LI> Optimum susceptibility front surface field (FSF) layer was 4.3 eV. </LI> <LI> Indium tin oxide (ITO) was used as FSF layer. </LI> <LI> 23.8%, 25.67% efficiency was obtained with 80, 20 nm thick ITO as FSF. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Impact of grain boundary defect on performance of perovskite solar cell

Iftiquar, S.M.,Yi, Junsin Elsevier 2018 Materials science in semiconductor processing Vol.79 No.-

<P>Methyl ammonium lead halide (MAPbI(3)) perovskite is a crystalline material. It shows interesting properties that are suitable for absorber layer of solar cell. An optimized solar cell requires 200-400 nm thick absorber layer. However, the thin absorber layer inevitably contains grain of crystallites and hence grain boundary (GB) defects. The GB defects affect device performance. Therefore, we theoretically investigated the effects of GB defects on performance of solar cells. In this simulation studies, we kept total mid-gap defect density (N-d) as constant at 4x10(17) cm(-3) but varied the GB defect density (GB(dd)) from 3x10(12) cm(-3) to 3x10(22) cm(-3), because of which, the observed short circuit current density (J(sc)) of the cells remain nearly unchanged, but the open circuit voltage (V-oc) and power conversion efficiency (PCE) decreased steadily, while the fill factor (FF) shows a different trend of variation in a region (Region-X, say) where the GB(dd) and the N-d were nearly equal. A further investigation reveals that in the Region-X, a transition happens from defect mediated recombination to GB mediated recombination, where the reverse saturation current density (J(0)) and diode ideality factor (n) of the solar cells, reduce sharply from 3.46x10(-13) A cm(-2) to 2.65x10(-19) A cm(-2) and 1.9 to 1.1, respectively for a cell with 200 nm thick absorber layer. For 400 nm thick absorber layer, reduction of these parameters was 1.96x10(-13) A cm(-2) to 1.20x10(-17) A cm(-2) and 1.8 to 1.2 respectively.</P>

Improved efficiency of perovskite-silicon tandem solar cell near the matched optical absorption between the subcells

Iftiquar, S M,Jung, Junhee,Yi, Junsin Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.40

<P>Current matching in a tandem solar cell is significant, because in a mismatched device the lowest current generating subcell becomes the current limiting component, and overall device efficiency remains lower than that could be obtained in the current matched device. Recent reports on methyl ammonium lead iodide (MAPbI<SUB>3</SUB>) based thin film solar cell has drawn interest to a perovskite-silicon tandem solar cell. Therefore, we investigated such a tandem solar cell theoretically. We used a MAPbI<SUB>3</SUB> based top and heterojunction with intrinsic thin layer silicon (HIT) bottom subcell. Optimization of the device structure was carried out by varying thickness of perovskite layer of top-cell from 50 to 1000 nm, while thickness of active layer of the HIT cell was kept constant, to 500 <I>µ</I>m. Single-junction solar cell, formed with the bottom subcell had open circuit voltage (<I>V</I> <SUB>oc</SUB>) of 705.1 mV, short circuit current density (<I>J</I> <SUB>sc</SUB>) of 28.22 mA cm<SUP>−2</SUP>, fill factor (FF) of 0.82 and efficiency of 16.4% under AM1.5G insolation. A relatively low thickness (150 nm) of the perovskite absorber layer was found optimum for the top-subcell to achieve best efficiency of the tandem cell, partly because of intermediate reflection at the interface between the two cells. We obtained a maximum of 20.92% efficiency of the tandem solar cell, which is higher by a factor of 1.27 from the starting HIT cell and a factor 1.47 higher from the perovskite cell efficiency. <I>J</I> <SUB>sc</SUB> of the optimized tandem cell was 13.06 mA cm<SUP>−2</SUP>. This was achieved near the matching optical absorption or current-density of the component subcells. For a practical application, the device used in our investigation was without textured front surface. An ordinary HIT bottom-cell was used with lower <I>J</I> <SUB>sc</SUB>. Therefore, with an improved HIT subcell, efficiency of the tandem cell, higher than 21% will be achievable.</P>

Investigation of highly efficient methyl ammonium lead halide perovskite solar cell with non-textured front surface

Iftiquar, S.M.,Kim, Jung Soo,Yi, Junsin WISSENSCHAFTLICHE VERLAGSGESELLSCHAFT MBH 2017 OPTIK -STUTTGART- Vol.148 No.-

<P><B>Abstract</B></P> <P>High quality methyl ammonium lead iodide (MAPbI<SUB>3</SUB>) perovskite material based single junction solar cell was investigated by simulation. We observed a systematic variation in device performance due to a variation in optical absorption of the active layer. By changing thickness of absorber layer from 50nm to 1000nm, we obtained power conversion efficiency (PCE) of the photovoltaic devices varying from 7.9% to 21.1%. Its open circuit voltage (<I>V<SUB>oc</SUB> </I>) varied from 1.26V to 1.16V, short circuit current density (<I>J<SUB>sc</SUB> </I>) varied from 7.56mA/cm<SUP>2</SUP> to 22.61mA/cm<SUP>2</SUP> while the fill factor (<I>FF</I>) remained constant at 83% in this variation. Front surface of the solar cell was kept non-textured, however, back reflection of unabsorbed light was used in the analysis. The maximum PCE of 21.1% and <I>J<SUB>sc</SUB> </I> of 22.61mA/cm<SUP>2</SUP> was observed for the solar cell with 1000nm absorber layer. The <I>J<SUB>sc</SUB> </I> and device efficiency increases with increased thickness of absorber layer (<I>d<SUB>i</SUB> </I>). Therefore, higher PCE can be obtained with a thicker absorber layer. However, we identify that, with 94nm thick absorber layer, the rate of change of PCE is equal to the rate of change of <I>J<SUB>sc</SUB> </I>, due to the thickness variation. In this cell with 94nm thick absorber layer (Cell-94), the PCE was 11.5%, nearly half of the PCE obtained with 1000nm absorber layer. In the Cell-94, the diode ideality factor was 2.04, and reverse saturation current density was 6×10<SUP>−13</SUP> Amp/cm<SUP>2</SUP>.</P>

Low Reverse Saturation Current Density of Amorphous Silicon Solar Cell Due to Reduced Thickness of Active Layer

Iftiquar, S M,Yi, Junsin The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.4

One of the most important characteristic curves of a solar cell is its current density-voltage (J-V) curve under AM1.5G insolation. Solar cell can be considered as a semiconductor diode, so a diode equivalent model was used to estimate its parameters from the J-V curve by numerical simulation. Active layer plays an important role in operation of a solar cell. We investigated the effect thicknesses and defect densities (N_d) of the active layer on the J-V curve. When the active layer thickness was varied (for N_d = 8×10¹⁷ cm^-3) from 800 nm to 100 nm, the reverse saturation current density (J_o) changed from 3.56×10^-5 A/cm² to 9.62×10^-11 A/cm² and its ideality factor (n) changed from 5.28 to 2.02. For a reduced defect density (N_d = 4×10¹⁵ cm^-3), the n remained within 1.45≤n≤1.92 for the same thickness range. A small increase in shunt resistance and almost no change in series resistance were observed in these cells. The low reverse saturation current density (J_o = 9.62×10^-11 A/cm²) and diode ideality factor (n = 2.02 or 1.45) were observed for amorphous silicon based solar cell with 100 nm thick active layer.