HIT Solar Cells Research Articles

수광층의 카바이드 함량 변화에 따른 실리콘 이종접합 태양전지 특성 변화

In this paper, the efficiency improvement of the heterojunction with intrinsic thin layer (HIT) solar cells is obtained by optimization process of p-type a-SiC:H as emitter. The optoelectronic of p-type a-SiC:H layers including the optical band-gap and conductivity under the methane gas content variation is conducted in detail. A significant increase in the Jsc by and Voc by 30 mV are attributed to enhanced photon-absorption due to broader band-gap of p-a-SiC:H and reduced band-offsets at p-side interface, respectively of HIT solar cells.

Enhancement in c-Si solar cells using 16 nm InN nanoparticles

In this work, 16 nm indium nitride (InN) nanoparticles (NPs) are used to increase the performance of thin-film c-Si HIT solar cells. InN NPs were spin-coated on top of an ITO layer of c-Si HIT solar cells. The c-Si HIT cell is a stack of 2 μm p type c-Si, 4–5 nm n type a-Si, 15 nm n+ type a-Si and 80 nm ITO grown on a p+ type Si substrate. On average, short circuit current density (Jsc) increases from 19.64 mA cm−2 to 21.54 mA cm−2 with a relative improvement of 9.67% and efficiency increases from 6.09% to 7.09% with a relative improvement of 16.42% due to the presence of InN NPs. Reflectance and internal/external quantum efficiency (IQE/EQE) of the devices were also measured. Peak EQE was found to increase from 74.1% to 81.3% and peak IQE increased from 93% to 98.6% for InN NPs coated c-Si HIT cells. Lower reflection of light due to light scattering is responsible for performance enhancement between 400–620 nm while downshifted photons are responsible for performance enhancement from 620 nm onwards.

Amorphous layers by electron beam evaporator deposition for hetero-junction with intrinsic thin layer solar cells applications

A low-cost process with electron beam evaporator deposition for amorphous layers was demonstrated in hetero-junction with intrinsic thin layer (HIT) solar cell. The cleaning process with saw damage removal procedure and the annealing temperature are also discussed in this work. The open-circuit voltage (Voc) and short-circuit current density (Jsc) were obtained as 285 mV and 2.9 mA/cm², respectively, with 5 min saw damage removal and 450°C forming gas annealing. Therefore, the low-cost process with the electron beam evaporator deposition could possibly fabricate the HIT solar cell and be a candidate for future higher performance photovoltaic device with optimisation process condition.

Interpretation of the degradation of silicon HIT solar cells due to inadequate front contact TCO work function

The degradation of the open circuit voltage (VOC) and of the I–V characteristics of p+/n amorphous silicon/crystalline silicon heterojunction solar cells (a-Si:H(p+/i)/c-Si(n) HIT cells) due to the use of transparent conducting oxide (TCO) with small work function at the front contact is investigated. The influence of the TCO work function on the band diagrams, carrier profiles and I–V characteristics in the dark and under illumination is studied by means of AFORS-HET device simulations supported by circuit modeling. It is found that when the TCO work function is not high enough to ensure a good ohmic contact with p-type heavily doped a-Si:H(p+) the VOC degradation is due to the rectifying Schottky barrier at the TCO/a-Si:H(p+) interface. On the other hand, if in addition to the small TCO work function the p-type active doping level in a-Si:H(p+) is reduced, the hole concentration in the p+ inversion layer emitter at the hetero-interface significantly drops leading to a strong enhancement of the emitter dark current and to serious VOC degradation. Moreover, if carrier recombination at the hetero-interface is significant, the weak inversion layer emitter may collapse at a relatively low cell voltage leading to total cell failure.

Highly textured conductive and transparent ZnO films for HIT solar cell applications

In this paper, aluminium-doped zinc oxide (AZO) thin-films were fabricated on both glass and silicon substrates by radio-frequency magnetron sputtering at various working pressures of 0.15–0.46 Pa. The effect of working pressure on the structural, electrical, and optical properties of the deposited AZO films was carefully studied. The lower working pressure is more favourable to large grain size, smooth surface, low electrical resistivity, and moderate optical transparency. For the AZO films deposited at lower working pressures, the larger grain size can be ascribed to the higher kinetic energy of the sputtered particles while the lower electrical resistivity is strongly related to both the presence of fewer grain boundaries due to the larger grain size and more activated amount of dopants in the films. We then applied AZO films deposited at 0.15 Pa to Al/AZO/n-a-Si : H/i-a-Si : H/p-c-Si/Al heterojunction Si solar cells with intrinsic thin layer (HIT) solar cells and achieved highly textured surfaces via acid etching. The HIT solar cells after acid texturing showed a higher external quantum efficiency (EQE) value than those with smooth AZO films mainly in the wavelength region from 300 to 500 nm, leading to an obvious increase in the conversion efficiency from 14.1% to 14.7%.

Detrimental Effect of Silicon Nanoparticles on P3HT:PCBM‐Based OPV Devices

Macromol. Chem. Phys. 2015, 216, 1155–1160 The authors wish to clarify misleading wording on page 4 of the manuscript. They did not use the same batch of solar cells as Chowdhury et al.; they used the same type of solar cell. The updated sentence is shown here: “To further investigate the solar cell degradation associated with the presence of Si-NPs, we tried to replicate the results shown by Chowdhury et al. (same type of c-Si HIT solar cells, same batch of Si-NPs stored and deposited under the same conditions, same equipment).”

Measurements and Simulations on the Mechanisms of Efficiency Losses in HIT Solar Cells

We study the electrical and the optical behavior of HIT solar cell by means of measurements and optoelectrical simulations by TCAD simulations. We compare the HIT solar cell with a conventional crystalline silicon solar cell to identify the strengths and weaknesses of the HIT technology. Results highlight different mechanisms of electrical and optical efficiency losses caused by the presence of the amorphous silicon layer. The higher resistivity of the a-Si layers implies a smaller distance between the metal lines that causes a higher shadowing. The worst optical coupling between the amorphous silicon and the antireflective coating implies a slight increase of reflectivity around the 600 nm wavelength.

InGaN thin films grown by RF sputtering for HIT solar cells

ABSTRACTThe wide range of optical band gaps of InGaN thin films led to considerable research in increasing the efficiency of solar cells. In this study, we present electrical, optical and structural properties of InGaN thin films grown by in situ rf sputtering method. Several samples of InGaN were deposited on aluminosilicate glass and silicon(111) substrates at different temperatures and varying N2 flow ratio. Growth temperatures are 35 °C, 150 °C, 200 °C. Aluminum metal contacts are deposited using DC sputtering method. Resistivity, mobility, conductivity values and their changes with respect to temperature are recorded using hall-effect measurement system. Band gap values and their changes with respect to N2 flow ratio in ( Ar+N2) mixture were calculated using UV spectrophotometer and tauc plots. Atomic composition was calculated using Energy-dispersive X-ray spectroscopy (EDX) analysis. Amorphous/crystalline nature of the samples are verified using XRD analysis.

Numerical simulations for high efficiency HIT solar cells using microcrystalline silicon as emitter and back surface field (BSF) layers

In present article the influence of thickness and band gap of microcrystalline silicon emitter layer, amorphous silicon front and back intrinsic layers and p-type crystalline silicon (c-Si) wafer thickness on the performance of TCO/μc-Si:H(n)/a-Si:H(i)/c-Si(p)/a-Si:H(i)/μc-Si:H(p+)/Ag Heterojunction with thin intrinsic layer (HIT) solar cell along with other structural possibilities were investigated through computer simulations using AFORS-HET software. These simulations revealed the importance of inclusion of intrinsic a-Si:H thin layer in improving the performance of solar cell with the help of interface passivation. Also microcrystalline BSF can raise the conversion efficiency more than 4% compared to HIT solar cell having no BSF layer. Highest stable efficiency of 24.12% for p-type substrate based HITBSF (HIT with back surface field) solar cells was observed. Furthermore the effect of textured transparent conductive oxide (TCO) on solar cells was investigated where the enhanced light trapping was observed with the use of textured TCO surface which raised the performance of solar cells. These optimizations may help in fabricating μc-Si emitter and BSF based HIT solar cells with stable efficiencies compared to possibly degraded efficiencies as in case of a-Si:H based HIT solar cell structures studied so far.

A statistical approach for the optimization of indium tin oxide films used as a front contact in amorphous/crystalline silicon heterojunction solar cells

In heterojunction silicon with intrinsic thin layer (HIT) solar cells, the excellent opto-electrical properties of indium tin oxide (ITO) front contact play a critical role in attaining high efficiency. Therefore, in this study, we present and demonstrate an effective statistic approach based on combining Taguchi method and Grey relational analysis for the optimization of ITO films. A reduction in the number of experiments by approximately 90% is obtained by the Taguchi method through an orthogonal array. The reproduction of the effect of process parameters on single performance characteristic, however, is still ensured. In addition, an excellent trade-off between electrical and optical properties of ITO films was attained within the selected range of parameters by Grey relational analysis at power density of 0.685W/cm2, working pressure of 0.4Pa, substrate temperature of 200°C, and post-annealing temperature of 200°C in 30min. Under optimal condition, the ITO films showed lowest electrical resistivity of 1.978×10−4Ωcm, and highest transmittance of 90.322%. The HIT solar cells using these ITO films as a front contact show highest efficiency of 16.616%, yielding a 1.750% absolute increase in efficiency compared to using ITO films with the initial condition. Furthermore, the analysis of variance (ANOVA) is determined to define the process parameters which have a dominant effect on the electrical and optical properties of ITO films. Based on ANOVA, we found that the substrate temperature was a key parameter which critically affects the opto-electrical properties of ITO films.

Simulation of the Bombardment to the Intrinsic Thin Layer of a-Si:H by Plasmas in the Hit Solar Cell

In the paper, the discharge process of double frequency capacitive coupled Plasma in argon gas has been investigated by one dimensional PIC/MCC method. The result shows that the rf voltage in fluence the density and Potential deeply. Furthermore, the effect of various driven voltage on ion energy distribution (IED) and ion angle distribution (IAD) at the electrode is studied. It is found that when the driven voltage grows, the Peak of energy increases. At the same time, the high energy ions distribution increase clearly too. The content of bombardment to the intrinsic thin layer of a-Si:H is analyzed in the condition of various driven voltage. The critical driven voltage is calculated, which can keep the plasma discharge process and not erode the intrinsic thin layer in the HIT solar cell.

RF magnetron sputtered ITO:Zr thin films for the high efficiency a-Si:H/c-Si heterojunction solar cells

ITO and ITO:Zr films with various thicknesses were prepared on glass substrates by RF magnetron sputtering. We observed a decrease in sheet resistance with increasing film thickness that in good agreement with Fuchs-Sondheimer theory. The ITO films doped with ZrO2 (∼0.2 wt%) showed improvement in some of the electrical and optical properties of ITO films. The surface roughness of ITO:Zr films increased with increasing film thickness. ITO:Zr films with thickness of 120 nm showed highest work function of 5.13 eV, as estimated from XPS data. The ITO:Zr films were employed as front electrodes in HIT solar cells; the best device performance was found to be: Voc = 710 mV, Jsc = 34.44 mA/cm2, FF = 74.8%, η = 18.30% at a thickness of 120 nm. A maximum quantum efficiency (QE) of 89% was recorded for HIT solar cells at a wavelength of 700 nm for 120 nm thick ITO:Zr films.

Simulation analysis of impact of silicon substrate selection on performance of heterojunction solar cells

The simulation of the electrical and optical behaviour of solar cell has been established as an essential tool for both improvement of existing devices and development of new ones. In this study, the effects of excess minority lifetime and concentration of n-c-Si on heterojunction solar cell performance are discussed to attempt to understand the possible key technique of 24·7% heterojunction with intrinsic thin layer (HIT) solar cell presented by Panasonic Company. Two basic models, Shockley–Read–Hall (SRH) recombination and Auger recombination equations, which can describe the recombination behaviour of carriers in the bulk of monocrystalline silicon, are discussed. This study improves the understanding of this device and to derive arguments for design optimisation. The simulated results show that the heterojunction solar cell has open circuit voltage of 0·75 V, short circuit current of 38·9 mA cm−2, fill factor of 0·836 and efficiency of 24·4% under the effective lifetime of 1×10−3 s, and substrate doping concentration of 1×1016 cm−3. These results of simulation can coincide with Panasonic’s latest 24·7% HIT solar cell.

Thin-film Si1−xGex HIT solar cells

We fabricated silicon–germanium (Si1−xGex) based HIT solar cells with x=0, 0.25, 0.41 and 0.56 in order to quantify the effect of germanium fraction on key solar cell performance parameters. The p-type absorber layer consists of 2 and 4μm Si1−xGex layer grown on p+ silicon substrate using a graded buffer layer to reduce the threading dislocation density. The emitter is n+ amorphous-Si. A thin strained-Si layer is grown on the c-Si1−xGex layer prior to a-Si deposition and is believed to improve a-Si–H/c-Si1−xGex interface quality. The short-circuit current (Jsc) increases, from ∼14mA/cm2 for Si cells to 21mA/cm2 for Si0.44Ge0.56 cells with 2μm-thick active layers, while open-circuit voltage decreases. The spectral response of the Si1−xGex solar cells improves due to a reduction in absorption depth and smaller band-gap associated with the higher germanium fractions.

Influence of high work function ITO:Zr films for the barrier height modification in a-Si:H/c-Si heterojunction solar cells

We report the influence of magnetron sputtered zirconium-doped indium tin oxide (ITO:Zr) films with high mobility and work function on the heterojunction with intrinsic thin layer (HIT) solar cell. The addition of oxygen (O2) to argon (Ar) flow ratio during the deposition process improves the Hall mobility of the ITO:Zr films while the carrier concentration decreased. The small amount of oxygen resulted in an enhancement of work function while excess amount of O2 was not suitable for the electrical and surface properties of ITO:Zr films. The increase of O2/Ar flow ratio from 0% to 0.4% improved the work function from 5.03 to 5.13eV while the conductivity of ITO:Zr films remained about the same. The ITO:Zr films were employed as a front anti-reflection layer in a HIT solar cell and the best photo-voltage parameters were found to be Voc=710mV, Jsc=33.66mA/cm2, FF=72.4%, and η=17.31% for the O2/Ar flow ratio of 0.4%. The increase of ITO:Zr work function leads to an increase in open circuit voltage (Voc) and fill factor (FF) of the device. Therefore, the ITO:Zr films with high work function can be used to modify the front barrier height in the HIT solar cell.

Efficiency Improvement of HIT Solar Cells on p-Type Si Wafers.

Single crystal silicon solar cells are still predominant in the market due to the abundance of silicon on earth and their acceptable efficiency. Different solar-cell structures of single crystalline Si have been investigated to boost efficiency; the heterojunction with intrinsic thin layer (HIT) structure is currently the leading technology. The record efficiency values of state-of-the art HIT solar cells have always been based on n-type single-crystalline Si wafers. Improving the efficiency of cells based on p-type single-crystalline Si wafers could provide broader options for the development of HIT solar cells. In this study, we varied the thickness of intrinsic hydrogenated amorphous Si layer to improve the efficiency of HIT solar cells on p-type Si wafers.

Simulation and Optimization of the Performance in Hit Solar Cell

The doping concentration and the thickness of different layers in the Hetero-junction with Intrinsic Thin layers solar cells (HIT) strongly influence their performances. We simulated, using AFORS-HET simulation software, the following layers structure: ZnO/a-Si:H(n)/a-Si:H(i)/c-Si(p)/a-Si:H(p)/Ag. We optimized the thicknesses and doping concentration of the emitter, buffer, absorber and the BSF layers.

The Amorphous/Crystalline Silicon Interface Research of HIT Solar Cells by Simulation

In this paper, we have focused on the influence of interface state density and band offsets on the performance of HIT solar cells by simulation. The interface state density Dithave negative influence on the open-circuit voltage VOC, fill factor FF and the short circuit current JSC, beyond different Ditrespectively. VOCdecreases monotonically with increasing Ditonly when Ditis greater than 1010cm-2, and for FF and JSCDitis 1012cm-2, 1013cm-2, respectively. Observed reduction in VOC(Ditis from 1×1010cm-2to 5×1013cm-2) may be due to the enhanced recombination possibility, which diminishes the difference in quasi Fermi energies from 0.8 eV to 0.46 eV. Reduction of JSC(Ditis from 1×1013cm-2to 5×1013cm-2) is connected with the carrier recombination rate that is heightened from 2.43×1024cm-3/s to 3.1×1026cm-3/s, which is markedly by two orders of magnitude. In addition, our research results demonstrate that by increasing the conduction band offset EC(from 0.09eV to 0.15 eV), the VOCcould be increased by 15.9 mV, while the performance of HIT solar cells is not affected by the valence band offset EV. The increase of ECresults in the rising of Vbiand thus improves VOC. It is worth mention that, the recombination potential VRecould be decreased from 232 meV to 208 meV by the increase of EC(from 0.09eV to 0.15eV) and thus is favorable to VOC. Consequently, when the interface state density is less than 1010cm-2and the conduction band offset reaches 0.15eV, we can optimize the performance of HIT solar cells to achieve 24.95% efficiency.

Analysis of the influence of buffer layer on p-a-Si/n-c-Si heterojunction solar cells

The influence mechanism of buffer layer on HIT solar cells is researched by AFORS-HET and MATLAB. First, P layer’s condition is optimized, result shows that high doping, thin thickness P layer should be chosen. Buffer layer have a twofold effect, the influence on density of interface state, and the energy band offsets between with crystalline silicon. Through calculation and simulation with AFORS-HET and MATLAB, it is found that when the density of interface state increases, the density of recombination center would increase, then open circuit voltage decreases. When the band mismatch increases, the interface minority carrier concentration would decline, open circuit voltage then improves. The influence of buffer layer on short circuit current and fill factor is small, but P layer’s condition has a relative bigger influence on them.

RF magnetron sputtered indium tin oxide films with high transmittance and work function for a-Si:H/c-Si heterojunction solar cells

The RF magnetron sputtered indium tin oxide (ITO) films were deposited on glass substrates with low resistivity, high transmittance and work function for various oxygen (O2) flow rates. The addition of small O2 contents during the sputtering process increased the Hall mobility of ITO films while carrier concentration was decreased. The work function of ITO films was enhanced from 4.31 to 4.81 eV through the growth of (222) plane having relatively low surface energy. The highly transparent ITO films were employed as front anti-reflection layer in heterojunction with intrinsic thin layer (HIT) solar cells and the best photo-voltage parameters were found to be; Voc = 665 mV, Jsc = 35.1 mA/cm2, FF = 73.2% and η = 17.1% for the O2 flow rate of 0.1 sccm. The high work function ITO films play an important role for barrier height modification in HIT solar cell.