Improving Device Efficiency for n-i-p Type Solar Cells with Various Optimized Active Layers

Iftiquar, Sk Md,Yi, Junsin The Korean Institute of Electrical and Electronic 2017 Transactions on Electrical and Electronic Material Vol.18 No.2

We investigated n-i-p type single junction hydrogenated amorphous silicon oxide solar cells. These cells were without front surface texture or back reflector. Maximum power point efficiency of these cells showed that an optimized device structure is needed to get the best device output. This depends on the thickness and defect density ($N_d$) of the active layer. A typical 10% photovoltaic device conversion efficiency was obtained with a $N_d=8.86{\times}10^{15}cm^{-3}$ defect density and 630 nm active layer thickness. Our investigation suggests a correlation between defect density and active layer thickness to device efficiency. We found that amorphous silicon solar cell efficiency can be improved to well above 10%.

Light Trapping in Silicon Based Tandem Solar Cell: A Brief Review

Iftiquar, Sk Md,Park, Hyeongsik,Dao, Vinh Ai,Pham, Duy Phong,Yi, Junsin Korea Photovoltaic Society 2016 Current Photovoltaic Research Vol.4 No.1

Among the various types of solar cells, silicon based two terminal tandem solar cell is one of the most popular one. It is designed to split the absorption of incident AM1.5 solar radiation among two of its component cells, thereby widening the wavelength range of external quantum efficiency (EQE) spectra of the device, in comparison to that of a single junction solar cell. In order to improve the EQE spectra further and raise short circuit current density ($J_{sc}$) an optimization of the tradeoff between the top and bottom cell is needed. In an optimized cell structure, the $J_{sc}$ and hence efficiency of the device can further be enhanced with the help of light trapping scheme. This can be achieved by texturing front and back surface as well as a back reflector of the device. In this brief review we highlight the development of light trapping in the silicon based tandem solar cell.

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.

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>

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.

Diode Equivalent Parameters of Solar Cell

Iftiquar, Sk Md,Dao, Vinh Ai,Yi, Junsin Korea Photovoltaic Society 2015 Current Photovoltaic Research Vol.3 No.4

Current characteristic curve of an illuminated solar cell was used to determine its reverse saturation current density ($J_0$), ideality factor (n) and resistances, by using numerical diode simulation. High efficiency amorphous silicon, heterojunction crystalline Si (HIT), plastic and organic-inorganic halide perovskite solar cell shows n=3.27 for a-Si and n=2.14 for improved HIT cell as high and low n respectively, while the perovskite and plastic cells show n=2.56 and 2.57 respectively. The $J_0$ of these cells remain within $7.1{\times}10^{-7}$ and $1.79{\times}10^{-8}A/cm^2$ for poorer HIT and improved perovskite solar cell respectively.

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>

Present Status and Prospects of Thin Film Silicon Solar Cells

Iftiquar, Sk Md,Park, Jinjoo,Shin, Jonghoon,Jung, Junhee,Bong, Sungjae,Dao, Vinh Ai,Yi, Junsin Korea Photovoltaic Society 2014 Current Photovoltaic Research Vol.2 No.2

Extensive investigation on silicon based thin film reveals a wide range of film characteristics, from low optical gap to high optical gap, from amorphous to micro-crystalline silicon etc. Fabrication of single junction, tandem and triple junction solar cell with suitable materials, indicate that fabrication of solar cell of a relatively moderate efficiency is possible with a better light induced stability. Due to these investigations, various competing materials like wide band gap silicon carbide and silicon oxide, low band gap micro-crystalline silicon and silicon germanium etc were also prepared and applied to the solar cells. Such a multi-junction solar cell can be a technologically promising photo-voltaic device, as the external quantum efficiency of such a cell covers a wider spectral range.

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>

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>