Silicon Heterojunction Technology Research Articles

Comparative experiment on the efficiency of water cooling in photovoltaic modules in the climatic conditions of Southern Russia

The problems of ensuring the safety of operation of nuclear power plants are always paid increased attention. In addition to the self-contained diesel generator sets used to maintain the operation of safety systems in case of loss of external power supply, it is also advisable to consider the use of more environmentally friendly self-contained photovoltaic units at this stage. The work is aimed at a comparative experimental study of the efficiency of water cooling in real natural climatic conditions of Southern Russia. In this experiment, cooled and uncooled photovoltaic modules are simultaneously exposed to a complex of variable weather factors: solar radiation, cloudiness, wind, pressure, temperature and humidity of the environment. Both modules have loads connected via MPPT controllers. The effect of water cooling on the energy efficiency of photovoltaic modules assembled from silicon heterojunction technology (HJT) solar cells was studied. The solar panels were made from 130 micron thick HJT cells interconnected using SmartWire contact technology. It reduces power loss due to possible defects such as cracks. The conditions for ensuring the highest degree of similarity between the parameters of the cooled and uncooled modules have been met. A comparative experimental study was conducted in Astrakhan State University using a long-term monitoring system for the characteristics of photovoltaic modules. This is a test photovoltaic system (TPS), built on the basis of the Paragraph PL2 electronic recorder. A significant increase in module output when working with cooling was established. At insolation of 987.5 W/m2, the power generated by the cooled module was 93.0297 W, while the power of the module without cooling was 79.306 W. The difference comprised 13.7237 watts. Power increased by 17%. In the experiment, the average efficiency value when the module was cooled was 0.15977. When uncooled, it was 0.13764. The efficiency intensified by 2.21%. This increase is significant. The results obtained confirm the fairly high efficiency of water cooling in photovoltaic modules in real natural operating conditions for regions with high ambient temperatures, Southern Russia, in particular

Modelling the use of PVSYST software for a stand-alone PV solar system "off grid" with batteries by utilizing silicon hetero-junction technology (HJT) panels in Iraq/Basra.

Fossil fuels have been widely used in electricity generation in recent years, resulting in excessive CO2 emissions. Continuing this would increase the temperature of the atmosphere, causing storms, hurricanes, droughts, dust storms, and flooding. Due to the fact that renewable energy produces few or no emissions, it has become increasingly important for it to be adapted in recent years. During the past few years, the PV sector has experienced rapid growth. New technology has enabled PV cells to become more efficient, and the sector is rapidly embracing new technologies. In this regard Silicon Hetero-junction technology HJT has been able to offer additional benefits: It is able to achieve efficiency levels above 24% at temperature 20C°. HJT solar panels have over 90% module bifaciallity and a low temperature coefficient (-0.24%/°C), which benefits to the levelized cost of energy (LCOE) and output power for PV systems. The objective of this study is to assess and compare the efficiency of high-quality (HJT) solar panels and SI-MONO solar panels for a residential off-grid system with at a peak power of 3 kWh and a daily power close to 20 kWh with a 48V system in Iraq/Basra. In order to calculate energy output, and enhance the system design, PVSYST (7.2.11 version) software was used. PVSYST's database contains meteorological data, including characteristics, solar radiation, and ambient temperature.

Four failure modes in silicon heterojunction glass-backsheet modules

Silicon heterojunction technology (HJT) is expected to gain a significant market share in the near future. For HJT to deliver a low levelized cost of electricity (LCOE), it needs to have a high initial efficiency and degrade less than 0.5% relative per year. This work investigates damp heat-induced failure modes in silicon HJT glass-backsheet modules. Four unique failure modes are identified after damp heat (DH) testing: point failure (Type-1); failure around the interconnected regions of the busbars and ribbon wires (Type-2); failure between the busbars (Type-3); and failure at/on the interconnected regions of busbars and ribbon wires (Type-4). The Type-1 failure mode is likely caused by a chemical reaction between surface contaminants (introduced to the cells during handling or characterization before encapsulation) and moisture that increase charge carrier recombination and lead to a loss in maximum power (Pmax) of up to 40%rel in this study. Type-2 and Type-3 failure modes cause Pmax losses of ∼5%rel and 50%rel, respectively, in this study and can appear due to exposure to soldering flux used for connecting the ribbon wires and busbars. Finally, the Type-4 failure mode causes a Pmax loss of ∼16%rel in this study after the DH test. The evidence suggests that this failure mode is likely due to the interaction of acetic acid, generated from a reaction between the encapsulation material and moisture, ribbon wires, and silver paste (busbars), resulting in recombination loss. We believe these failure modes must be well understood and mitigated at preferably the solar cell level to ensure that HJT can meet its LCOE potential.

Prediction of sub-pyramid texturing as the next step towards high efficiency silicon heterojunction solar cells

The interfacial morphology of crystalline silicon/hydrogenated amorphous silicon (c-Si/a-Si:H) is a key success factor to approach the theoretical efficiency of Si-based solar cells, especially Si heterojunction technology. The unexpected crystalline silicon epitaxial growth and interfacial nanotwins formation remain a challenging issue for silicon heterojunction technology. Here, we design a hybrid interface by tuning pyramid apex-angle to improve c-Si/a-Si:H interfacial morphology in silicon solar cells. The pyramid apex-angle (slightly smaller than 70.53°) consists of hybrid (111)0.9/(011)0.1 c-Si planes, rather than pure (111) planes in conventional texture pyramid. Employing microsecond-long low-temperature (500 K) molecular dynamic simulations, the hybrid (111)/(011) plane prevents from both c-Si epitaxial growth and nanotwin formation. More importantly, given there is not any additional industrial preparation process, the hybrid c-Si plane could improve c-Si/a-Si:H interfacial morphology for a-Si passivated contacts technique, and wide-applied for all silicon-based solar cells as well.

Silicon heterojunction solar cells with up to 26.81% efficiency achieved by electrically optimized nanocrystalline-silicon hole contact layers

Silicon heterojunction (SHJ) solar cells have reached high power conversion efficiency owing to their effective passivating contact structures. Improvements in the optoelectronic properties of these contacts can enable higher device efficiency, thus further consolidating the commercial potential of SHJ technology. Here we increase the efficiency of back junction SHJ solar cells with improved back contacts consisting of p-type doped nanocrystalline silicon and a transparent conductive oxide with a low sheet resistance. The electrical properties of the hole-selective contact are analysed and compared with a p-type doped amorphous silicon contact. We demonstrate improvement in the charge carrier transport and a low contact resistivity (<5 mΩ cm2). Eventually, we report a series of certified power conversion efficiencies of up to 26.81% and fill factors up to 86.59% on industry-grade silicon wafers (274 cm2, M6 size).

Long‐term performance and reliability of silicon heterojunction solar modules

AbstractThe high‐efficiency silicon heterojunction (SHJ) technology is now perceived mature enough to enter the Giga‐Watt manufacturing scale with several players around the globe. The growth of the SHJ technology requires confidence from manufacturers, investors, and system developers about its reliability and long‐term performance. In this work, we perform a literature survey collecting performance data (and performance loss rates [PLRs]) published for SHJ modules. Publications on this specific subject are still limited; however, enough available data exist to drive some preliminary conclusions. Despite a long list of caveats specific to this type of meta‐analysis, when considering all published datasets, we obtain for SHJ modules median and average PLR values of 0.56%/year and 0.70%/year, respectively. These numbers are in line with PLR generally reported for field‐deployed crystalline silicon (c‐Si modules). We then apply a filtering procedure to distinguish what we perceive to be high‐accuracy datasets from less accurate ones. This methodology is understandably arbitrary, but it helps increasing the robustness of the present analysis. Our refined analysis leads us to slightly higher PLR for SHJ modules: 0.80%/year and 0.83%/year for median and average values, respectively. These values fall between previously reported PLR of c‐Si and thin‐film modules. Additionally, we observe some mild correlations between the PLRs and the climatic conditions of the installation sites, even if we need to stress that for each climate, we find a large variability, including a PLR value as low as 0.29%/year. We complement the survey with information about the main failure modes reported in the literature for this technology and an analysis of the limits and caveats for this type of study. The most significant one is that the reported numbers refer—for the vast majority—to modules from just one manufacturer (i.e., the first company manufacturing and commercializing the SHJ technology). We finally point out that a deep understanding of the potential weaknesses of the technology—collected over the years—has led to several improvements in terms of reliability. A careful material choice and module design may in fact allow the SHJ technology targeting extended service lifetimes of 35+ years.

Design and Simulation of a PV Solar System with Silicon Hetero-Junction Technology (HJT) for a Residential Stand-Alone "off Grid" System with Batteries Using PV Syst Software in Iraq/Baghdad

Recently, the environment has been negatively impacted by the excessive CO2 emissions caused by the wide usage of fossil fuels in electricity generation. If this continued, it is predicted that the temperature of the atmosphere would rise, causing an increase in storms, hurricanes, droughts, dust, and floods. Therefore, as renewable energy produces little to no emissions, there is an urgent need to adapt it in recent times. Meanwhile, The PV sector has experienced rapid growth in recent years. The PV sector is embracing new technology, and the cell efficiency has been rising rapidly like Silicon Hetero- junction technology HJT which has offered additional benefits: It offers a well-suited application to reach efficiencies above 23% with process temperatures below 200°C. HJT solar panels have &gt;90% module bifaciality and a low temperature coefficient (-0.3 %/C°), and provide additional benefit to the Levelized Cost of Energy LCOE and output power for PV systems. This study intends to assess the efficiency of a residential off-grid system with (HJT) PV panels at a total power of 2.0 kWh and the daily power close to 10 KWh/day with a 48V system in Iraq/Baghdad. PVsyst (7.2.11 version) software has been used for the analysis to calculate the energy output, and enhancing the system design. The characteristics, solar radiation, and ambient temperature are also included in the meteorological data used for evaluation, which is taken from PVsyst's database.

Fully Textured, Production-Line Compatible Monolithic Perovskite/Silicon Tandem Solar Cells Approaching 29% Efficiency.

Perovskite/silicon tandem solar cells are promising avenues for achieving high-performance photovoltaics with low costs. However, the highest certified efficiency of perovskite/silicon tandem devices based on economically matured silicon heterojunction technology (SHJ) with fully textured wafer is only 25.2% due to incompatibility between the limitation of fabrication technology which is not compatible with the production-line silicon wafer. Here, a molecular-level nanotechnology is developed by designing NiOx /2PACz ([2-(9H-carbazol-9-yl) ethyl]phosphonic acid) as an ultrathin hybrid hole transport layer (HTL) above indium tin oxide (ITO)recombination junction, to serve as a vital pivot for achieving a conformal deposition of high-quality perovskite layer on top. The NiOx interlayer facilitates a uniform self-assembly of 2PACz molecules onto the fully textured surface, thus avoiding direct contact between ITO and perovskite top-cell for a minimal shunt loss. As a result of such interfacial engineering, the fully textured perovskite/silicon tandem cells obtain a certified efficiency of 28.84% on a 1.2-cm2 masked area, which is the highest performance to date based on the fully textured, production-line compatible SHJ. This work advances commercially promising photovoltaics with high performance and low costs by adopting a meticulously designed HTL/perovskite interface.

Outdoor performance of GaAs/bifacial Si heterojunction four-terminal system using optical spectrum splitting

Bifacial photovoltaics and multijunction systems represent the most promising alternatives to overcome the theoretical limit of single-junction Si photovoltaics, and these solutions can also be combined to achieve higher performances. This work investigates the outdoor performance of a bifacial four-terminal photovoltaic system based on combining a III-V semiconductor with the silicon heterojunction technology. By exploiting the wide band gap energy of GaAs, the bifaciality of the Si heterojunction and the spectrum-splitting capability of dichroic mirrors, an optimal voltage match between mini-modules of the two solar cells was achieved, with an open-circuit voltage mismatch of 4% of the average value. In this study, we demonstrate the full functionality of bifacial operation with a 17% increase of power conversion efficiency throughout the day compared to monofacial operation. Furthermore, we show that though the solar spectrum is subjected to strong variations from morning to afternoon, which lead to changes of the ratio of the GaAs to the Si mini-module short-circuit currents up to 43% throughout the day, the variation of the overall system power conversion efficiency remains quite limited, less than 16% of the maximum value thanks to the efficient coupling of the two mini-modules.

Optoelectrical analysis of TCO+Silicon oxide double layers at the front and rear side of silicon heterojunction solar cells

Silicon Heterojunction has become a promising technology to substitute passivated emitter and rear contact (PERC) solar cells in pursuance of lower levelized cost of electricity through high efficiency devices. While high open circuit voltages and fill factors are reached, current loss related to the front and rear contacts, such as the transparent conductive oxide (TCO) layers is still a limiting factor to come closer to the efficiency limit of silicon based solar cells. Furthermore, reducing indium consumption for the TCO has become mandatory to push silicon heterojunction technology towards a terawatt scale production due to material scarcity and costs. To address these issues dielectric layers, such as silicon dioxide or nitride cappings are implemented to reduce TCO thicknesses both diminishing parasitic absorption and material consumption. However, reducing the TCO thickness comes in cost of resistive losses. Furthermore, the TCO properties do vary with thickness and neighboring layer configuration altering the optimization frame of the device. In this paper we present a detailed analysis to quantify the optoelectrical losses trade-off associated to the TCO thickness reduction in such layer stacks. Through the analysis we show and explain why experimental bifacial cells with 20 nm front and rear TCO perform at a similar level to reference cells with 75 nm under front and rear illumination reaching efficiency close to 24% at 92% bifaciality. We present as well a simple interconnection method via screen printing metallization to implement a thin TCO/silicon dioxide/silver reflector enhancing current density from 39.6 to 40.4 mA/cm 2 without compromising resistive losses resulting in a 0.2% absolute solar cell efficiency increase from a bifacial design (23.5–23.7%). Finally, following this approach we present a certified champion cell with an efficiency of 24.6%. • Analysis of TCO variations on electron and hole contact for Si heterojunction solar cells by simulations and experiments. • Both sides 20 nm TCO + SiO 2 layer stack SHJ solar cells with 23.9% efficiency. • Champion solar cell with rear 20 nm TCO + SiO 2 layer stack and silver rear reflector with 24.6% efficiency.

Nanocrystalline‐silicon hole contact layers enabling efficiency improvement of silicon heterojunction solar cells: Impact of nanostructure evolution on solar cell performance

AbstractHydrogenated amorphous silicon (a‐Si:H) is a key enabler in high‐efficiency crystalline silicon solar cells known as the silicon heterojunction technology. Although efforts have been devoted to replacing doped a‐Si:H contact layer by hydrogenated nanocrystalline silicon (nc‐Si:H) to take advantage of its superior optoelectrical properties, it is still unclear whether the nc‐Si:H outperforms the a‐Si:H at the high efficiency level. Here, we show that boron‐doped (p)nc‐Si:H prepared by plasma‐enhanced chemical vapor deposition (PECVD) acts as an efficient hole contact layer, providing not only a mitigation of the parasitic absorption loss but also improvements in passivation and electrical contact properties. This results in an efficiency increase by 0.3%–0.6% absolute compared to the reference cell with the (p)a‐Si:H, and a best cell efficiency of 23.54%. We find that the critical thickness of the (p)nc‐Si:H layers required for gaining high efficiency (tc ~ 15–30 nm) is a factor of 3–6 greater than that of the (p)a‐Si:H. UV Raman spectroscopy and electrical conductivity measurements reveal that the tc of the (p)nc‐Si:H is associated with the layer growth needing for the surface coalescence of nanocrystals, determining the hole selectivity and the contact resistivity at the electrode/(p)nc‐Si:H interface. Our results suggest that such nanostructure evolution can be hastened by using a very‐high‐frequency PECVD process.

The race for the best silicon bottom cell: Efficiency and cost evaluation of perovskite–silicon tandem solar cells

AbstractPerovskite–silicon tandem solar cells have shown a rapid progress within the past 5 years in terms of their research cell efficiency and are currently being investigated as candidates for the next generation of industrial PV devices. This raises the question of which silicon bottom cell will be most suitable for tandem application. Currently, the silicon heterojunction (SHJ) technology dominates in tandem research achieving world records. However, it is an open issue of how to transfer these research results to industrial mass production, which is driven by cost reduction and resource efficiency and includes challenges like upscaling and long‐term stability. Therefore, it is highly relevant for the PV industry to get reliable and predictive estimates on the efficiency and cost potential, as well as technologically feasible solutions. In this work, we elaborate on silicon bottom cell concepts based on the PERC, TOPCon, and SHJ technology combined with two different interconnection concepts. For each tandem device, the efficiency potential is investigated by means of an experimentally validated simulation model. Second, we evaluate the bottom cell concepts in terms of all‐in cell costs per piece. Bringing the efficiency potential and cost evaluation together allows us to assess the different tandem cell concepts in terms of all‐in module cost per watt peak. Our results show that perovskite–silicon tandem devices are promising candidates to significantly reduce the levelized cost of electricity and, in particular, that the “race” for the best silicon bottom cell is still open to all the investigated bottom cell technologies.

(Keynote) Development History of High Efficiency Silicon Heterojunction Solar Cell- from Discover to Practical Use

Silicon heterojunction (SHJ) solar cells are attracting attention as high-efficiency Si solar cells. The basicSHJ structure is p-type amorphous Si (a-Si)/i-type (non-doped) a-Si/n-type mono-crystalline Si (c-Si). Wehave developed and actively evolved this SHJ solar cells from early 1990s, and introduced the moduleequipped with SHJ solar cells named as well-known “HIT”. The features of HIT are: (1) high efficiency,(2) good temperature characteristics, that is, a small output decrease even in the temperature environmentactually used, (3) easy application to double-sided power generation (bifacial module) using symmetricstructure. Although bifacial module has been receiving much attention in recent years, we launched it asearly as 2000.How was this excellent solar cell born? Originally, it was born in the process of developing thin-filmpolycrystalline Si (poly-Si) solar cells as the bottom cells of tandem-type solar cells with a-Si top cells.As an initial stage of the development, we used p-type a-Si as a window layer and n-type c-Si wafer as aphotovoltaic layer because the characteristics of c-Si was clearer than thin film poly-Si. The insertion of ilayerbetween p-type a-Si and n-type c-Si came from two ideas to improve the interface properties. Onewas a structural approach (control the Si bonding network between c-Si and a-Si with microcrystal bufferlayer), and the other was an attempt to suppress the mutual diffusion of impurities. For the former, it wasconfirmed that it was better to use a-Si instead of microcrystals to passivate the c-Si surface effectively,and for the latter, it was found that better characteristics could be obtained by surface passivation of ilayerwith few defects, instead of the effect of impurity separation. The surface passivation technologyusing amorphous semiconductor film was a new invention different from conventional passivation usinginsulating films such as SiOx and SiNx. With this new structure, a large improvement of about 30 mV inopen circuit voltage (Voc) was confirmed. Next we applied this approach to the back side, and again wefound that i-layer could greatly reduce interface defects. Thus, the basic structure of the symmetrical SHJsolar cell was determined. With this structure (Ag electrode/TCO/(p/i)-a-Si/n-c-Si/(i/n)-a-Si/TCO/Agelectrode), we achieved a conversion efficiency of 20% (cell size of 1 cm x 1 cm) in 1994, and after thatthe efforts for mass production started. To expand to a practical size, we newly developed the electrodeforming technology using low-temperature curing type silver paste, and successfully started the massproduction in 1997.In parallel, our R&D team continued to make various conversion efficiency improvements whichincluded optimizing a-Si deposition conditions, developing new TCO materials and deposition methods,and lowering the resistivity of silver paste. In addition, we succeeded in demonstrating in experiments forthe first time that the open-circuit voltage increased associated with the thinning of wafers that had beenpredicted in simulations. The excellent surface passivation capability of i-layer minimized losses whenthinning wafers and maintained the conversion efficiency, which was a very advantageous feature fromthe viewpoint of cost reduction. At the end of 2012 (announced in 2013), we achieved a cell conversionefficiency of 24.7% with a wafer thickness of 98 μm, demonstrating that both low cost and highefficiency can be obtained. Some of these technologies were introduced into mass production.In 2014, we applied SHJ technology the back-contact type solar cell, and achieved a conversionefficiency of 25.6% with both the high Isc due to elimination of front electrode and the high Voc due toexcellent surface passivation. This was a new world record at that time for non-concentrating siliconbasedsolar cells at the research level, the previous one having stood for 15 years.

High-efficiency Crystalline Silicon Solar Cells: A Review

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 PERC, IBC, HIT, and 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.

Advanced Graphene-Based Transparent Conductive Electrodes for Photovoltaic Applications.

New architectures of transparent conductive electrodes (TCEs) incorporating graphene monolayers in different configurations have been explored with the aim to improve the performance of silicon-heterojunction (SHJ) cell front transparent contacts. In SHJ technology, front electrodes play an important additional role as anti-reflectance (AR) coatings. In this work, different transparent-conductive-oxide (TCO) thin films have been combined with graphene monolayers in different configurations, yielding advanced transparent electrodes specifically designed to minimize surface reflection over a wide range of wavelengths and angles of incidence and to improve electrical performance. A preliminary analysis reveals a strong dependence of the optoelectronic properties of the TCEs on (i) the order in which the different thin films are deposited or the graphene is transferred and (ii) the specific TCO material used. The results shows a clear electrical improvement when three graphene monolayers are placed on top on 80-nm-thick ITO thin film. This optimum TCE presents sheet resistances as low as 55 Ω/sq and an average conductance as high as 13.12 mS. In addition, the spectral reflectance of this TCE also shows an important reduction in its weighted reflectance value of 2–3%. Hence, the work undergone so far clearly suggests the possibility to noticeably improve transparent electrodes with this approach and therefore to further enhance silicon-heterojunction cell performance. These results achieved so far clearly open the possibility to noticeably improve TCEs and therefore to further enhance SHJ contact-technology performance.

The amazing improvement of silicon heterojunction technology: ready for a true mass market launch

The amazing improvement of silicon heterojunction technology: ready for a true mass market launch

Silicon heterojunction solar cells: Recent technological development and practical aspects - from lab to industry

We review the recent progress of silicon heterojunction (SHJ) solar cells. Recently, a new efficiency world record for silicon solar cells of 26.7% has been set by Kaneka Corp. using this technology. This was mainly achieved by remarkably increasing the fill-factor (FF) to 84.9% - the highest FF published for a silicon solar cell to date. High FF have for long been a challenge for SHJ technology. We emphasize with the help of simulations the importance of minimised recombination, not only to reach high open-circuit voltages, but also high FF, and discuss the most important loss mechanisms. We review the different cell-to-module loss and gain mechanisms putting focus on those that impact FF. With respect to industrialization of SHJ technology, we discuss the current hindrances and possible solutions, of which many are already present in industry. With the intrinsic bifacial nature of SHJ technology as well as its low temperature coefficient record high energy production per rated power is achievable in many climate regions.

Homo-heterojunction concept: From simulations to high efficiency solar cell demonstration

The novel solar cell architecture called silicon homo-heterojunction (HHJ) cell is investigated combining experimental and simulation approaches. This structure intends to overcome the limitations of the silicon heterojunction technology regarding the amorphous/ crystalline silicon interface (p) a-Si:H/(i) a-Si:H /(n) c-Si) by the addition of a (p+) c-Si layer at the hetero-interface. First, the added (p+) c-Si layer is experimentally investigated using boron implantation through the realization and characterization of symmetric solar cell precursors. An adapted process flow taking into account the (p+) c-Si profile optimization, the annealing effects on substrate degradation, and the impact on surface passivation, is deeply explored. Then, large area solar cells are processed and the solar cell performance are discussed in view of the data obtained on precursors and with the help of realistic numerical simulations. Overall, we observe that the HHJ solar cells exhibit a small performance improvement compared to reference heterojunction cells. In particular, a gain in the fill factor is observed, which is shown to be originated from both an improvement in field effect and a decrease of the vertical series resistance from the a-Si:H layers. The experimental data obtained on the processed homo-heterojunction solar cells confirm that this technology can lead to improved conversion efficiencies compared to the high quality reference heterojunction solar cells.

Optimized Metallization for Interdigitated Back Contact Silicon Heterojunction Solar Cells

We report on the design and manufacturing of interdigitated back contact cells based on the silicon heterojunction technology. The influence of geometry and overlap of the doped amorphous silicon layers forming the contact fingers on device performance have been investigated by simulation. Two contact formation concepts, with and without a TCO interlayer – an indium tin oxide/silver (ITO/Ag) stack, and a direct aluminum (Al) metallization – are experimentally evaluated. The former retains good passivation but leads to a too high contact resistivity, the latter shows the opposite behavior, but yields a slight benefit in terms of overall performance achieving more than 20% of efficiency. We show that in this case a contact system is formed whose properties can be tuned by annealing, enabling a trade‐off between VOC and FF.Structure of the presented solar cell; a SiNX layer covers the front side, the rear side is passivated by overlapping layer stacks of intrinsic and doped amorphous silicon, the latter are contacted by aluminum.

A cost roadmap for silicon heterojunction solar cells

Research and development of silicon heterojunction (SHJ) solar cells has seen a marked increase since the recent expiry of core patents describing SHJ technology. SHJ solar cells are expected to offer various cost benefits compared to conventional crystalline silicon solar cells. This paper analyses the production costs associated with five different SHJ cell designs, including an interdigitated back-contacted (IBC) design. Using life-cycle costing, we analyzed the current cost breakdown of these SHJ designs, and compared them to conventional diffused junction monocrystalline silicon modules. Coupling the results for current designs with literature data on technological improvements, we also present a prospective analysis of production costs for the five SHJ cells and modules.For current designs, module costs were calculated to be 0.48–0.56 USD per Watt-peak (Wp) for SHJ modules, compared to 0.50USD/Wp for a conventional c-Si module. The efficiency bonus for SHJ modules compared to conventional c-Si modules is offset by a strong increase in metallization costs for SHJ designs, as comparatively large amounts of low-temperature silver-paste are required. For module materials, the requirement for conductive adhesives results in a small cost penalty for SHJ modules compared to c-Si modules, which is more than balanced by the effect of higher efficiency in SHJ modules.Our prospective study showed that improvements in cell processing and module design could result in a significant drop in production costs for all module types studied. The SHJ modules gain much advantage by reducing and replacing silver consumption, increased cell efficiency and thinner wafers and have prospective production costs of 0.29–0.35USD/Wp. Conventional c-Si module cost is less sensitive to silver paste consumption, limiting the potential for cost reduction, and has prospective production costs of 0.33USD/Wp. Replacement of indium-tin-oxide was not found to contribute substantially to a reduction in module costs.