Intrinsic Thin Layer Research Articles

HIT Solar Cell With V20x Window Layer

ABSTRACTIn the conventional crystalline silicon heterojunction solar cell with the intrinsic thin layer structure (the HIT solar cell), a p-doped thin film silicon or its alloy (pDTF-Si/A) is used as the hole collecting window layer. However, the parasitic absorbance in the pDTF-Si/A window layer, and the toxic, explosive diborane gas used for p-doping are limiting factors for achieving HIT cells with reduced processing costs and / or higher efficiencies. In this work, pDTF-Si/A is replaced by V2Ox, which is deposited by a simple physical vapor deposition technique. Due to the wide band gap of V2Ox, the HIT solar cell with the V2Ox window layer generates a higher short-circuit current density than the reference conventional HIT cell under 1 sun, and achieves an open-circuit voltage of 0.7 V. Furthermore, the charge carrier lifetime and pseudo-efficiency values of the HIT solar cell with the V2Ox window layer indicate that this cell has the potential to outperform the conventional HIT cell in terms of the power conversation efficiency under the standard test conditions.

Improvement of the recombination and infrared light losses by rear surface chemical polishing in silicon heterojunction solar cells

Rear surface chemical polishing (RSCP) was investigated for the improvement of the internal reflection and surface passivation of heterojunction solar cells with intrinsic thin layers (HIT). The HIT solar cells without or with RSCP treatment were prepared by plasma-enhanced chemical vapor deposition and physical vapor deposition techniques. Scanning electron microscopy results showed that rounding of the spires and V-groove bottom of the pyramid as well as smoothing of incline surface of the pyramid were achieved. These effects would decrease the loss of infrared light transmittance and interface recombination at the rear surface of the cells. To experimentally corroborate these two points, two special geometries, ITO/c-Si/hydrogenated amorphous silicon (a-Si:H)/ITO and a-Si:H/c-Si/a-Si:H, were introduced as a test of the reflectance/transmittance spectra and the minority carrier lifetime. Weakened transmittance and enhanced lifetime were observed for the sample with RSCP, which are responsible for the improvement of J sc and V oc, respectively. Therefore, RSCP is a promising candidate for improving the performance of HIT solar cells.

Photon-trapping microstructures enable high-speed high-efficiency silicon photodiodes

High-speed, high-efficiency photodetectors play an important role in optical communication links that are increasingly being used in data centres to handle higher volumes of data traffic and higher bandwidths, as big data and cloud computing continue to grow exponentially. Monolithic integration of optical components with signal-processing electronics on a single silicon chip is of paramount importance in the drive to reduce cost and improve performance. We report the first demonstration of micro- and nanoscale holes enabling light trapping in a silicon photodiode, which exhibits an ultrafast impulse response (full-width at half-maximum) of 30 ps and a high efficiency of more than 50%, for use in data-centre optical communications. The photodiode uses micro- and nanostructured holes to enhance, by an order of magnitude, the absorption efficiency of a thin intrinsic layer of less than 2 µm thickness and is designed for a data rate of 20 gigabits per second or higher at a wavelength of 850 nm. Further optimization can improve the efficiency to more than 70%. Light-trapping nanoscale holes are exploited to improve the speed and efficiency of silicon photodiodes with intrinsic layers less than 2 μm thick.

이종접합 실리콘 태양전지 적용을 위한 선택적 전하접합 층으로의 전이금속산화물에 관한 연구

Hydrogenated Amorphous Silicon (a-Si:H) is used as an emitter layer in HIT (heterojunction with Intrinsic Thin layer) solar cells. Its low band gap and low optical properties (low transmittance and high absorption) cause parasitic absorption on the front side of a solar cell that significantly reduces the solar cell blue response. To overcome this, research on CSC (carrier Selective Contacts) is being actively carried out to reduce carrier recombination and improve carrier transportation as a means to approach the theoretical efficiency of silicon solar cells. Among CSC materials, molybdenum oxide (<TEX>$MoO_x$</TEX>) is most commonly used for the hole transport layer (HTL) of a solar cell due to its high work function and wide band gap. This paper analyzes the electrical and optical properties of <TEX>$MoO_x$</TEX> thin films for use in the HTL of HIT solar cells. The optical properties of <TEX>$MoO_x$</TEX> show better performance than a-Si:H and <TEX>${\mu}c-SiO_x:H$</TEX>.

Performance assessment of five different photovoltaic module technologies under outdoor conditions in Algeria

The aim of this paper is to establish a performance assessment of different kinds of photovoltaic (PV) module technologies installed in the city of Saida in Algeria. The modules are three thin film modules: copper indium selenide (CIS), mono-crystalline heterojunction with intrinsic thin layer (HIT) and tandem structure of amorphous silicon and microcrystalline silicon (a-Si_μc-Si) with two crystalline silicon modules: multi-crystalline and mono-crystalline back contact. The modules were characterised by measuring their I-V characteristics under the same outdoor conditions. Moreover, measurements of various meteorological parameters such as irradiance, temperature and humidity, using the weather station, were also performed. The monthly average daily performance parameters as performance ratio, energy yield and efficiency are given and analysed. It was found that the HIT and the a-Si_μc-Si performed much better than the other technologies. The annual average daily performance ratios of a-Si_μc-Si module was found to be about 1.55% higher compared to HIT module and 2.04% compared to CIS. The HIT module produce an annual average daily energy of 1.15 kWh more than double what the a-Si_μc-Si produce and an annual average daily efficiency more than double of the efficiency of a-Si_μc-Si.

Multiscale modeling of transport in silicon heterojunction solar cells

Silicon based single junction solar cell technology continued to make significant strides in the past year with new world record module efficiencies being reported for the Panasonic heterojunction with thin intrinsic layer (HIT) module (23.8%) and the SunPower rooftop silicon module (24.1%). The HIT cell which is comprised of amorphous silicon (a-Si) and crystalline silicon (c-Si) currently holds the world record efficiency (25.6%) for a silicon based single junction solar cell. Further improvement in this technology requires a rigorous understanding of the underlying physics of the device. The device performance of a-Si and c-Si heterojunction solar cells depends heavily on the nature of transport at the hetero interface and defect assisted transport through the a-Si. Different microscopic processes dominate transport in different regions of the device and take place across widely varying time scales. In this work we present a multiscale model which utilizes different simulation methodologies to study physics in various regions of the device, namely, the Ensemble Monte Carlo (EMC), Kinetic Monte Carlo (KMC), and Drift Diffusion (DD) solvers. The EMC studies the behavior of the photogenerated carriers at the heterointerface; the KMC analyzes transport of the photogenerated carriers through the intrinsic amorphous silicon (i-a-Si) barrier layer; and the DD solver calculates current and other device properties in the low field regions of the cell. These solvers are then self consistently coupled to analyze device performance. Previously, our KMC simulations have shown that hopping is the main mode of transport through the i-a-Si, and the photogenerated carries are collected by defect emission rather that Poole - Frenkel emission or direct tunneling1. In addition, using EMC simulations we have shown that the photogenerated carriers exhibit non Maxwellian behavior at the heterointerface2. This work specifically describes the self-consistent coupling of the DD and EMC solvers. By adding the EMC solver to the multiscale solver we are able to capture the high field behavior of the photogenerated carriers, and its affect on device parameters such as JSC, VOC, FF and efficiency.

Effect of Different Photovoltaic Materials on Energetic and Exergetic Performance of Photovoltaic Thermal Arrays

The study presents the effect of packing factor of Photovoltaic (PV) module on the room temperature, cell temperature and efficiency of a proposed Building Integrated Semi-transparent Photovoltaic Thermal (BiSPVT) and Building Integrated Opaque Photovoltaic Thermal (BiOPVT) systems with duct mounted on the roof of the building. Different PV materials like mono-crystalline silicon (m-Si), amorphous silicon (a-Si), poly-crystalline silicon (p-Si), cadmium telluride (CdTe), copper indium selenide (CIS) and hetero-junction with intrinsic thin layer (HIT) have been considered in the analysis under the cold climatic condition of India. Since Srinagar (India) has the cold climatic condition, therefore, its climatic data has been considered in the present analysis.

Radial Junction Silicon Nanowire Photovoltaics With Heterojunction With Intrinsic Thin Layer (HIT) Structure

Single-wire radial p-i-n heterojunction with intrinsic thin layer nanowire solar cell devices were fabricated by plasma-enhanced chemical vapor deposition of thin intrinsic and n-type hydrogenated amorphous silicon (a-Si:H) shell layers on p-type silicon nanowires synthesized by vapor–liquid–solid growth. The thin intrinsic a-Si:H layer provided an effective passivation of the crystalline Si nanowire surface, and the corresponding device exhibits a dark current density of ${1.6 \times 10}^{-7}\,{\text {A}/ \text{cm}}^{2}$ . Under one-sun illumination, the device shows a short-circuit current ( $I_{\rm{sc}}$ ) of ${ 2.66 \times 10}^{- 7}$ mA, open-circuit voltage ( $V_{\rm{oc}}$ ) of 0.46 V, fill factor (ff) of 0.52, and energy conversion efficiency ( η ) of 6.3%. Indium tin oxide (ITO) contacts were also deposited on the n-type shell as an antireflection layer to improve light absorption in the nanowire device. After ITO deposition, the device exhibited a larger $I_{\rm{sc}}$ of 2.75 × 10–7 mA, but the overall efficiency decreased due to a larger leakage current and lower $V_{\rm{oc}}$ .

Deposition of Intrinsic a-Si:H by ECR-CVD to Passivate the Crystalline Silicon Heterointerface in HIT Solar Cells

We have deposited intrinsic amorphous silicon (a-Si:H) using the electron cyclotron resonance (ECR) chemical vapor deposition technique in order to analyze the a-Si:H/c-Si heterointerface and assess the possible application in heterojunction with intrinsic thin layer (HIT) solar cells. Physical characterization of the deposited films shows that the hydrogen content is in the 15–30% range, depending on deposition temperature. The optical bandgap value is always comprised within the range 1.9–2.2 eV. Minority carrier lifetime measurements performed on the heterostructures reach high values up to 1.3 ms, indicating a well-passivated a-Si:H/c-Si heterointerface for deposition temperatures as low as 100 oC. In addition, we prove that the metal–oxide–semiconductor conductance method to obtain interface trap distribution can be applied to the a-Si:H/c-Si heterointerface, since the intrinsic a-Si:H layer behaves as an insulator at low or negative bias. Values for the minimum of D it as low as 8 × 1010 cm-2⋅eV-1 were obtained for our samples, pointing to good surface passivation properties of ECR-deposited a-Si:H for HIT solar cell applications.

Modeling the Temporal Variations in the Output of Large Solar PV Power Plants

With the rapid increase in the cumulative installations around the world, solar PV technology has started playing a major role in the global clean energy scenario. One of the major challenges for the large scale integration of solar energy with the power grids is its intermittent nature. In this paper, temporal variations in the power output of six different solar PV technologies are quantified and modeled. The solar cells considered are single crystalline, poly crystalline, micro crystalline amorphous silicon, copper Indium Selenium (CIS) and hetero-junction with intrinsic thin layer (HIT). Three years of performance data from a 1.2 MW experimental solar PV farm in Brunei Darussalam were used for the modeling. It was found that the variations in the PV output follow the Cauchy's probability distribution. Ramping down behaviour of the solar panel was critically analyzed and expected ramp downs at 95% confidence level are presented. HIT modules showed the highest ramp rate among the panels, whereas CIS showed the lowest fluctuations.

Estimation of Most Frequent Conditions and Performance Evaluation of Three Photovoltaic Technology Modules

In this paper, a performance evaluation technique using most frequent conditions (MFC) for accurate design of photovoltaic systems, based on energy rating and site-specific standards is reported. Most frequent conditions are estimated for the three different technologies: multicrystalline silicon (mc-Si), amorphous silicon (a-Si), and hetero-junction with intrinsic thin layer (HIT) for the site based on air-mass, module temperatures, incident in-plane irradiance, and power output. The performances are analyzed over a period of 3 years by evaluating changes in the performance ratio, the energy yields, and the percentages of occurrence of data points corresponding to standard test condition (STC), nominal operating cell temperature (NOCT), and MFC. For MFC, performance ratio (PR) values are ranging from 0.70 to 0.83, 0.70 to 0.86, and 0.70 to 0.90 for mc-Si, a-Si, and HIT, respectively. The total energy yield of HIT is the highest followed by a-Si and mc-Si modules for this climatic zone.

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.

The synergistic effect of air mass on outdoor performance for different PV module in India

ABSTRACTThe effect of air mass (AM) on the performance of multi-crystalline silicon (m-Si), amorphous silicon (a-Si), and hetero-junction with intrinsic thin layer (HIT)-technology-based photovoltaic (PV) modules are evaluated for representative day of four seasons during the year 2011 for composite climate of India. To find the best performing PV module technology with respect to AM at the site, annual energy yields and performance ratio against different AM bands (AM 1–4.5) are plotted. It is found that HIT modules perform better than m-Si and a-Si at each AM band. Annual energy yields for all three technologies decrease with increasing order of AM bands. The performance ratio for HIT and m-SI modules initially increases and then decreases with increasing order of AM bands. However, for a-Si modules, the performance ratio decreases with increasing order of the AM bands.

Numerical Study of TCO/Silicon Solar Cells with Novel Back Surface Field

ZnS/Si/CuO heterostructure is investigated by a theoretical approach as a possible low-cost design for photovoltaic conversion in the track of the heterojunction with intrinsic thin layer solar cells. Our results indicate that, owing to perfect electron affinity and lattice matching properties, zinc sulfide with adequate Al doping can efficiently replace zinc oxide window layer as an emitter region for silicon-based solar cells. Lattice mismatch, energy band alignment at the interfaces and material resistivity are the framework parameters of the study. By focusing on the open circuit voltage parameter, the back metal/Si and silicon base doping were optimized so that the conversion efficiency was increased from 3.37% to 15.19%. The introduction of a cupric oxide (CuO) layer acting as a p + back surface field with a bandgap of 1.35 eV and appropriate doping as high as 7 × 1018 cm−3 can enhance the conversion efficiency to 17.30%, provided that the silicon material remains free from contamination by copper atoms and also by performing a suitable treatment of CuO to lower its resistivity.

Core–Shell Heterojunction Solar Cells Based on Disordered Silicon Nanowire Arrays

Heterojunction with intrinsic thin layer (HIT) solar cells are still costly due to the use of silicon wafers that contribute to ∼30% of the final module cost. To reduce the costs, thinner wafers can be used but to the detriment of the optical absorption. This loss has to be compensated by an efficient light trapping scheme. In this paper we study HIT devices based on Si nanowire (SiNW) core–shell structures to enhance light absorption. The SiNWs are fabricated by a wet etching technique, and the heterojunction is formed using an optimized low-temperature plasma enhanced chemical vapor deposition (PECVD) process at 200 °C. The solar cells are characterized via carrier lifetime and electron beam induced current (EBIC) measurements to understand their electrical properties at nanoscale. The impact of the SiNW length on the cell performance is also investigated. The solar cells show a good performance reaching average fill factor of 81%, Voc of 0.525 V, and Jsc of 29.27 mA/cm2 giving rise to an average effici...

Commercial photovoltaic system design for Cardiff City Hall

The rooftops of Cardiff City Hall were surveyed to establish potential areas for commercial-scale photovoltaic (PV) system design. The orientation and tilt angles of suitable unshaded roof areas were measured for accurate PV system simulation. The performance of two PV technologies, polycrystalline silicon (p-Si) and heterojunction with intrinsic thin layers (HIT) was investigated. From the analysis of simulation, experimental, environmental and economic data, HIT was found to be the best-performing PV technology for system installation. Superior performance of HIT under diffuse sunlight conditions, typical of the UK climate, was demonstrated. Additionally, the maximum power temperature coefficient, verified during experimental work, was lower than the p-Si alternative (−0·28 against −0·50%/°C). Electricity demand data for City Hall were analysed and 8·1% of the annual electricity demand (solar fraction) could be supplied by an 88 kWp HIT PV system. The HIT PV system modelled would significantly improve the energy performance of Cardiff City Hall, avoiding &gt;40 000 kg carbon dioxide emissions annually. The levelised cost of energy from one array (B, £0·11/kWh) was less than the current day tariff rate for grid import (£0·1173). The economic and environmental benefits of well-designed high-efficiency PV systems in the UK at commercial scale are also demonstrated.

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.

Assessment of Rear-Surface Processing Strategies for III–V on Si Multijunction Solar Cells Based on Numerical Simulations

The manufacturing of high-efficiency III–V on Si multijunction solar cells needs the development of hybrid, i.e., adapted to both families of materials, solar cell processing techniques, able to extract the full photovoltaic potential of both the subcells. This fact especially impacts the processing of the silicon rear surface of the tandem, which cannot receive treatments commonly used in the single-junction Si solar cell industry [Al-back surface field (BSF), thermal SiO2, and so on], since these would result in an excessive thermal load that would deteriorate the III–V upper layers (top cell, tunnel junction, and buffer layer). However, the Si bottom cell requires an advanced design with good rear passivation, a good ohmic contact, and good carrier selectivity, so that its contribution to the efficiency of the tandem is maximized. Accordingly, in this paper, several low-temperature compatible rear-surface passivation techniques for the Si bottom subcell in a monolithic III–V/Si tandem solar cell are explored. In particular, aluminum BSFs, passivated emitter and rear cell (PERC)-like architecture, passivated emitter and rear locally diffused (PERL)-like architecture formed with low thermal loads, and heterojunction with intrinsic thin layer (HIT)-like processes are assessed using numerical simulations, and a comparison of the Si bottom cell performance for the mentioned alternatives in a GaAsP/Si dual-junction solar cell is presented.

Electrically Active Defects In Solar Cells Based On Amorphous Silicon/Crystalline Silicon Heterojunction After Irradiation By Heavy Xe Ions

Abstract The contribution is focused on the diagnostics of structures with a heterojunction between amorphous and crystalline silicon prepared by HIT (Heterojunction with an Intrinsic Thin layer) technology. The samples were irradiated by Xe ions with energy 167 MeV and doses from 5 × 108 cm−2 to 5 × 1010 cm−2. Radiation defects induced in the bulk of Si and at the hydrogenated amorphous silicon and crystalline silicon (a-Si:H/c-Si) interface were identified by Deep Level Transient Spectroscopy (DLTS). Radiation induced A-centre traps, boron vacancy traps and different types of divacancies with a high value of activation energy were observed. With an increased fluence of heavy ions the nature and density of the radiation induced defects was changed.

Analytical study of a-Si:H/c-Si thin heterojunction solar cells with back surface field

In this paper, the high efficiency TCO-n(aSi:H)-i(aSi:H)-p(c-Si)-$$\hbox {p}^{+}$$p+(aSi:H) heterojunction with intrinsic thin-layer (HIT) solar cell is analyzed. The effects of the intrinsic thin-layer and the back surface field (BSF) on the photovoltaic parameters of thin solar cells are discussed. The analytical results show that the intrinsic layer inserted at the a-Si:H/c-Si interface decreases the density of interface states. If the interface state density is lower than $$10^{11}\,\hbox {cm}^{-2}$$1011cm-2 in the presence of an intrinsic thin layer a-Si:H, the effect of recombination current density on the photovoltaic parameters becomes low. The BSF formed by hydrogenated amorphous silicon layer can increase the conversion efficiency by about 2.6 % and the open-circuit voltage to $$\sim $$~80 mV as compared to the HIT solar cell wherein the BSF is realized by crystalline silicon. The results obtained from the simulation studies are in good agreement with the literature, and might open promising opportunities for enhancing the design parameters of HIT cells.