• Energy Research

Light- and elevated-temperature-induced degradation (LeTID) in p-type multicrystalline silicon has a severe impact on the effective minority carrier lifetime of silicon and remains a crucial challenge for solar cell manufacturers. The precise cause of the degradation is yet to be confirmed; however, several approaches have been presented to reduce the extent of degradation. This paper presents insights on the impact of thermal budgets and cooling rates during post-firing illuminated anneals and their role in changing the lifetime and mitigating LeTID for thermal processes between 350 and 500 °C. We demonstrate that the thermal budget of these processes plays a crucial role in LeTID suppression and that the cooling rate only plays a role during short treatment durations (≤1 min). For the parameter space studied, we show that annealing for an appropriate time and temperature can both enhance the minority carrier lifetime and completely suppress the LeTID, with the injection-dependent Shockley–Read–Hall lifetime analysis indicating that the recombination activity of the LeTID defects in the bulk has been eliminated. Finally, this paper demonstrates a process that results in a stable lifetime after 800 h of conventional light-soaking at 75 °C.

Abstract Both buried contact solar cells (BCSC) and laser doped selective emitter (LDSE) solar cells have achieved considerable success in large-scale manufacturing. Both technologies are based on plated contacts. High metal aspect ratios achieved by BCSC allow low shading loss while the buried metal contacts in the grooves provide good contact adhesion strength. In comparison, although the LDSE cell achieves significantly higher efficiencies and is a much simpler approach for forming the selective emitter region and self-aligned metal plating, the metal adhesion strength falls well short of that achieved by the BCSC. Recent studies show that plated contacts based on the latter can be more durable than screen-printed contacts. This work introduces a new concept of laser doping with grooving to form narrow grooves with heavily doped walls in a simultaneous step, with the self-aligned metal contact subsequently formed by plating. This process capitalizes on the benefits of both BCSC and LDSE cells. The laser-doped grooves are only 3–5 µm wide and 10–15 µm deep; the very steep walls of these grooves remain exposed even after the subsequent deposition of the antireflection coating (ARC). This unique feature significantly reduces the formation of laser-induced defects since the stress due to the thermal expansion mismatch between the ARC and silicon is avoided. Furthermore, the exposed walls allow nucleation of the subsequent metal plating. This novel structure also benefits from greatly enhanced adhesion of the plated contact due to it being buried underneath the silicon surface in the same way as the BCSC. Cell efficiencies over 19% are achieved by using this technology on p -type Czochralski (Cz) wafers with a full area aluminum (Al) back surface field (BSF) rear contact. It is expected that much higher voltages and consequently higher efficiencies could be achieved if this technology is combined with a passivated rear approach.

AbstractIn this work, we integrate defect engineering methods of gettering and hydrogenation into silicon heterojunction solar cells fabricated using low‐lifetime commercial‐grade p‐type Czochralski‐grown monocrystalline and high‐performance multicrystalline wafers. We independently assess the impact of gettering on the removal of bulk impurities such as iron as well as the impact of hydrogenation on the passivation of grain boundaries and B‐O defects. Furthermore, we report for the first time the susceptibility of heterojunction devices to light‐ and elevated temperature–induced degradation and investigate the onset of such degradation during device fabrication. Lastly, we demonstrate solar cells with independently verified 1‐sun open‐circuit voltages of 707 and 702 mV on monocrystalline and multicrystalline silicon wafers, respectively, with a starting bulk minority‐carrier lifetime below 40 microseconds. These remarkably high open‐circuit voltages reveal the potential of inexpensive low‐lifetime p‐type silicon wafers for making devices with efficiencies without needing to shift towards n‐type substrates.

La numérisation permet d'accéder à un réseau intégré de mégadonnées inexploitées avec des avantages potentiels pour la société et l'environnement. Le développement de systèmes intelligents connectés à l'Internet des objets peut générer des opportunités uniques pour relever stratégiquement les défis associés aux objectifs de développement durable (ODD) des Nations Unies afin de garantir une société équitable, durable sur le plan environnemental et saine. Cette perspective décrit les opportunités que la numérisation peut offrir pour construire la société durable de l'avenir. Les technologies intelligentes sont envisagées comme des outils révolutionnaires, leur intégration bénéficiant aux trois éléments essentiels du lien entre l'alimentation, l'eau et l'énergie : (i) la production alimentaire durable ; (ii) l'accès à une eau potable propre et salubre ; et (iii) la production et l'utilisation d'énergie verte. Il discute ensuite des avantages de la numérisation pour catalyser la transition vers des pratiques de fabrication durables et améliorer le bien-être de la santé des citoyens en fournissant un accès numérique aux soins, en particulier pour les communautés mal desservies. Enfin, la perspective englobe les avantages de la numérisation en fournissant une vision holistique de la manière dont elle peut contribuer à relever les graves défis de la biodiversité de la planète menacée et du changement climatique. La digitalización proporciona acceso a una red integrada de macrodatos sin explotar con beneficios potenciales para la sociedad y el medio ambiente. El desarrollo de sistemas inteligentes conectados al internet de las cosas puede generar oportunidades únicas para abordar estratégicamente los desafíos asociados con los Objetivos de Desarrollo Sostenible (ODS) de las Naciones Unidas para garantizar una sociedad equitativa, ambientalmente sostenible y saludable. Esta perspectiva describe las oportunidades que la digitalización puede brindar para construir la sociedad sostenible del futuro. Las tecnologías inteligentes se conciben como herramientas que cambian el juego, por lo que su integración beneficiará a los tres elementos esenciales del nexo alimentos-agua-energía: (i) producción sostenible de alimentos; (ii) acceso a agua potable limpia y segura; y (iii) generación y uso de energía verde. Luego discute los beneficios de la digitalización para catalizar la transición hacia prácticas de fabricación sostenibles y mejorar el bienestar de la salud de los ciudadanos al proporcionar acceso digital a la atención, particularmente para las comunidades desatendidas. Finalmente, la perspectiva engloba los beneficios de la digitalización al proporcionar una visión holística sobre cómo puede contribuir a abordar los graves desafíos de la biodiversidad del planeta en peligro y el cambio climático. Digitalization provides access to an integrated network of unexploited big data with potential benefits for society and the environment. The development of smart systems connected to the internet of things can generate unique opportunities to strategically address challenges associated with the United Nations Sustainable Development Goals (SDGs) to ensure an equitable, environmentally sustainable, and healthy society. This perspective describes the opportunities that digitalization can provide towards building the sustainable society of the future. Smart technologies are envisioned as game-changing tools, whereby their integration will benefit the three essential elements of the food-water-energy nexus: (i) sustainable food production; (ii) access to clean and safe potable water; and (iii) green energy generation and usage. It then discusses the benefits of digitalization to catalyze the transition towards sustainable manufacturing practices and enhance citizens' health wellbeing by providing digital access to care, particularly for the underserved communities. Finally, the perspective englobes digitalization benefits by providing a holistic view on how it can contribute to address the serious challenges of endangered planet biodiversity and climate change. توفر الرقمنة الوصول إلى شبكة متكاملة من البيانات الضخمة غير المستغلة مع فوائد محتملة للمجتمع والبيئة. يمكن أن يؤدي تطوير الأنظمة الذكية المتصلة بإنترنت الأشياء إلى خلق فرص فريدة لمواجهة التحديات المرتبطة بأهداف الأمم المتحدة للتنمية المستدامة (SDGs) بشكل استراتيجي لضمان مجتمع عادل ومستدام بيئيًا وصحي. يصف هذا المنظور الفرص التي يمكن أن توفرها الرقمنة نحو بناء مجتمع مستدام في المستقبل. يُنظر إلى التقنيات الذكية على أنها أدوات لتغيير قواعد اللعبة، حيث سيفيد دمجها العناصر الأساسية الثلاثة للعلاقة بين الغذاء والماء والطاقة: (1) الإنتاج الغذائي المستدام ؛ (2) الوصول إلى مياه الشرب النظيفة والمأمونة ؛ و (3) توليد الطاقة الخضراء واستخدامها. ثم يناقش فوائد الرقمنة لتحفيز الانتقال نحو ممارسات التصنيع المستدامة وتعزيز رفاهية صحة المواطنين من خلال توفير الوصول الرقمي إلى الرعاية، لا سيما للمجتمعات المحرومة. أخيرًا، يجذب المنظور فوائد الرقمنة من خلال تقديم رؤية شاملة حول كيفية المساهمة في مواجهة التحديات الخطيرة للتنوع البيولوجي للكوكب المهدد بالانقراض وتغير المناخ.

Polysilicon (poly-Si)-on-oxide passivating contact structures (POLO/TOPCon) enable high-efficiency solar cells as they simultaneously provide a very high level of surface passivation and a high conductance for either electrons or holes. The ease of incorporation with existing manufacturing lines and their tolerance for high-temperature processing has increased the wide acceptance of this structure in the PV industry. In this report, we explore the effects of short high-temperature annealing required for effective hydrogenation and formation of ohmic screen-printed contacts across a wide temperature range (636 °C–846 °C) on the stability of passivating contact structures. We study this on p-type c-Si substrates with phosphorus-doped (n-type) or boron-doped (p-type) polysilicon contacts capped with either an AlOx or SiNx coating. Our experimental results show that irrespective of the poly-Si doping type, AlOx-capped samples suffer a loss in surface passivation across the investigated temperature range, while SiNx-capped samples show an improvement at lower annealing temperatures. Above 744 °C, severely ruptured blisters occur for the samples coated with a SiNx layer, leading to lift-off of the poly layer in extreme cases, and in all cases, significant surface passivation losses, up to 99%. A study of the long-term stability of these fired samples under 1-sun illumination @ 140 °C shows that they suffer from both bulk and surface-like instabilities. Two degradation cycles were observed: the first, a boron-oxygen light-induced degradation (BO-LID) observed after 5 min, with capture cross-section ratios of 15.8–19.2, and a slower secondary degradation, similar to light and elevated temperature-induced degradation (LeTID), with maximum degradation reached after ∼ 14 days. The presence of a silicon nitride layer does not appear to influence the kinetics of post-degradation recovery. Our results suggest that the effect of firing may be influenced by the polarity of the bulk c-Si or perhaps the chemistry of the SiNx film and highlight that passivating contact structures based on p-type c-Si may offer better long-term stability than those based on n-type c-Si.

In this paper, the physical mechanisms involved in electron-beam-induced current (EBIC) imaging of semiconductor pn-junctions are reviewed to propose a model and optimize the acquisition of experimental data. Insights are drawn on the dependence of the EBIC signal with electron accelerating voltage and surface conditions. It is concluded that improvements in the resolution of EBIC are possible when the surface conditions of the specimens are carefully considered and optimized. A lower accelerating voltage and an increase of the surface recombination velocities are quantitatively shown to maximize the EBIC lateral resolution in locating the pn-junction. The effect of surface band bending is included in the model, and it is seen to primarily affect the surface recombination. Introducing controlled surface damage is shown as a potential method for resolution enhancement via focused ion beam milling with Ga+ ions. These findings contribute to the understanding of this technique and can produce further improvements to its application in semiconductor device technology.

AbstractLONGi Solar Energy Technology Co. Ltd. has achieved 23.83% for a commercial p‐type Cz PERC cell. From a batch of over 40 000 cells, the average line efficiency achieved was 22.5%. R&D studies investigating hydrogenation and degradation show the importance of hydrogenation processes for efficiency improvements and controlling the hydrogen to prevent light‐induced degradation. Such degradation is shown to appear very differently under different illumination and temperature conditions. This degradation impacts VOC, ISC, and especially fill factor. Current injection and thermal anneal can be used to recover the degradation, but the recovery may not be stable. Reducing the hydrogen content within the cell is shown to minimise degradation without sacrificing performance, provided that enough hydrogen is retained to passivate boron‐oxygen defects.