In the relentless pursuit of solar efficiency, back contact (BC) technology has emerged as a frontrunner, pushing the boundaries of what is possible with crystalline silicon cells. To discuss its further potential, Lü Fang from the Photovoltaic Committee of the China Green Supply Chain Alliance hosted the “Embracing the New: BC Symbiosis” Leadership Dialogue in Zhuhai, China, at the end of November 2024.
The event, organized by ISC Konstanz, brought together top executives from 2 of the world’s leading BC manufacturers – Chen Gang, Chairman of AIKO, and Zhong Baoshen, Chairman of LONGi Green Energy – alongside an academic perspective from Prof. Shen Wenzhong, Director of the Solar Research Institute at Shanghai Jiao Tong University. The dialogue revolved around BC technology’s transformative potential and the importance of collaboration among industry leaders to drive its development.
AIKO’s Chairman Gang opened the discussion by highlighting BC as the only technology that can get close to the theoretical conversion efficiency of crystalline silicon of 29.56%, which makes it the best technology from a theoretical standpoint. It optimizes optical and electrical properties through a grid-free front surface and by minimizing recombination losses via passivated contacts, allowing it to utilize sunlight fully. The design also brings unmatched aesthetics giving a uniform appearance with the absence of a grid on the front side. The technology has a few other advantages. Unlike HJT, it doesn’t require rare elements like indium. Many of the BC contenders have been able to implement silver-free metallization, making the technology free from the precious metal. Gang underscored that BC now offers unparalleled customer value within crystalline silicon technologies, setting the stage for its widespread adoption.
Fully in line with the above highlights, LONGi’s Chairman Baoshen Zhong further emphasized that the advancements in passivation techniques inevitably converge on BC. He then also highlighted that the collaborative efforts by AIKO, LONGi, and other key players of the segment have addressed prior cost challenges tied to BC’s complex structures. Zhong highlighted that BC now offers unparalleled customer value within crystalline silicon technologies, paving the way for its large-scale adoption.
Wenzhong from Solar Research Institute further underscored BC’s growing recognition, particularly in China, where it gained significant traction in 2024. He noted that apart from AIKO and LONGi, several leading companies are preparing to launch BC production lines, signaling industry-wide confidence in the technology’s future. Attributing this progress to China’s robust industrial ecosystem, Wenzhong said that it has driven innovation in critical processes like laser patterning, cleaning, and passivation. He pointed out that BC’s inherent design – allowing independent optimization of the front and rear surfaces – delivers superior efficiency compared to competing technologies. With ongoing industrial and technological support, Wenzhong affirmed that BC is well-positioned to lead the solar sector into a new era of high efficiency and cost competitiveness.
Both LONGi and AIKO emphasized their commitment to innovation and collaboration in advancing BC technology. LONGi’s Zhong highlighted the solar industry’s progress over the past 20 years, crediting innovation and perseverance as its driving forces. He shared LONGi’s approach of tackling challenges through first-principles reasoning, citing the company’s key decision in 2006 to focus entirely on monocrystalline silicon over polycrystalline. This strategic shift, based on efficiency, cost, and reliability analysis, led to groundbreaking advancements like RCZ crystal growth technology and the establishment of China’s diamond wire cutting supply chain. Zhong noted that LONGi began researching back-contact (BC) technology in 2016-2017, aligning with AIKO. Their joint evaluation reaffirmed BC’s potential as a transformative technology for crystalline silicon, which Zhong called irreplaceable for revitalizing the PV industry.
Aligning to these views, AIKO’s Chen recounted the companies’ early collaboration during the monocrystalline era with LONGi’s wafers. Together, the companies identified PERC as the ultimate p-type technology and developed low-cost tubular PERC innovations. Now, in the current n-type era, the 2 companies share the vision that sees BC as the ultimate technology. Despite being first conceptualized in 1985, BC faced commercialization delays due to its complexity. However, AIKO and LONGi recognized its disruptive potential and initiated BC research nearly at the same time, in 2016-2017, and BC is now in mass production offering a strong customer value proposition. However, one area where BC technology currently lags behind its counterparts is its relatively lower bifaciality. But Chen emphasized that it is only 3% lower than TOPCon in theory, with over 75% achieved in practice for ground-mounted systems. AIKO also has plans for 85% bifacial ABC cells within the next 2-3 years.
BC technology, while over 2 decades in development, only recently gained significant momentum, particularly in China, where advancements have outpaced earlier international efforts. Leading companies have pushed performance to new heights. BC commercial modules have been ruling the efficiency space for over 2 years now. However, the technology is still in its nascent stages with significant potential for further enhancement, according to Shen. He discussed the structural evolution of BC and its future prospects. LONGi’s HPBC 1.0 transitioning to HPBC 2.0, incorporating n-type wafers and full passivation, is one example. There is also ongoing research exploring integrating HJT structures to improve efficiency, such as replacing p-poly with amorphous or microcrystalline silicon. This could improve passivation and controllability, and ultimately result in improved Voc and better fill factor, according to Shen. He referenced LONGi’s HJT world record efficiency of 27.3%, suggesting BC could achieve 28% or more in future iterations. Front-side optimization, including advanced passivation and anti-reflection coatings, is also a focus area.
Efficiency is critical, but cost reduction is equally essential for the widespread adoption of any technology. Metallization gets the first mention in this content. However, companies have already mastered silver-free metallization, which is part of the roadmap for others. Chen also highlighted China’s robust PV ecosystem, which fosters collaboration among material providers, technology developers, and laser manufacturers to drive further cost reductions. He expressed strong confidence that BC technology will undergo a rapid evolution over the next 3 to 5 years, leading to substantial improvements in efficiency, cost, and overall performance.
LONGi’s Zhong also acknowledged that efficiency is the first milestone of market competitiveness, but also pointed out processing aspects such as passivation, damage reduction, and laser precision that still need to be optimized. He emphasized LONGi’s investments in cost-reduction strategies, including the adoption of base metals like aluminum and copper, are expected to further enhance competitiveness.
Discussing future developments in store, Chen announced that AIKO will soon launch 25%-efficiency modules, with a roadmap to achieve 26% or more within 1 to 2 years. This efficiency roadmap is closely tied to low-oxygen, high-resistance silicon wafers, which will be used in future product generations. He also highlighted AIKO's full-screen modules, which increase the active cell area by 5 to 8% compared to non-BC modules.
BC technology was initially perceived as suitable only for rooftop applications. Challenging this perception, Zhong said LONGi introduced a ground-mounted BC product in Spain, followed by distributed BC solutions. He emphasized that BC excels across applications, offering superior conversion efficiency, excellent bifacial ratios, and robust performance even in challenging terrains and shaded conditions. Zhong described BC technology’s advantages using the metaphor “high, rich, handsome, and safe.” “High” signifies its high efficiency, energy output, and technically advanced; “Rich” refers to its superior financial returns; “Handsome” reflects its aesthetic appeal; and “Safe” highlights its enhanced hotspot protection, with module temperatures under shading limited to around 100°C, which is significantly lower than the 170-120°C for traditional modules. To illustrate BC’s value, Zhong cited a Zhuhai case study where replacing a conventional module with a BC module added 35 W of capacity, generating an additional 40 kWh annually. At a daytime electricity rate of RMB 0.75/kWh, this equates to an extra RMB 30 per year. With BC module costs below RMB 90, the investment achieves payback in under 3 years, delivering tenfold returns over 30 years.
Picking on the safety aspects of BC, AIKO’S Chen emphasized the enhanced reliability of BC modules, particularly for distributed systems, outlining 3 key safety benefits. First, BC modules mitigate fire risks through superior hotspot prevention and temperature control. Second, these products provide structural safety, demonstrating reliability across lightweight, single-glass, and double-glass formats. Third, they provide investment protection by ensuring long-term performance and safeguarding financial returns. Chen highlighted BC’s unmatched reliability in power generation, attributed to its single-sided interconnection design, which minimizes the risk of microcracks. As an example, he cited a collaboration with Huaneng on a floating system demonstration, where BC modules outperformed TOPCon modules by generating 7% more power per watt in the first month. Floating systems, prone to impacts and vibrations, often exacerbate microcracks, but BC modules’ superior crack resistance enhances their reliability and performance under such conditions.
Answering a question on the timeline for BC products to achieve a 50% market share, LONGi’s Zhong reflected on a wager he made during SNEC 2024. While the initial estimate was 2029, he now revised it to 2027/2028, citing rapid technological progress. He noted, however, that while rapid adoption is promising from a technological perspective, it presents challenges for manufacturers, such as the risk of overcapacity, which would require careful management.
Sharing his view on the timeline for BC adoption, AIKO’s Chen emphasized the need for a strategic approach. He gauged audience interest in continued TOPCon investment, noting the muted response as an indicator for the industry to shift focus towards emerging technologies like BC. Chen emphasized that achieving large-scale BC production with high efficiency and low cost will require a 2-3-year timeframe while highlighting the importance of avoiding the pitfalls of overcapacity looming around TOPCon. Both LONGi and AIKO's leadership concurred that a gradual, strategic rollout would be advantageous for the industry, ultimately establishing BC as the dominant technology in photovoltaics.
Shen reasoned out from the efficiency perspective, highlighting BC technology’s efficiency advantage over TOPCon, with BC cell mass production efficiency expected to reach 27.5% to 28%, compared to TOPCon’s current efficiency of around 25.3%. An average annual efficiency improvement of 0.4% to 0.5% indicates that BC is poised to dominate the market within 5 years, potentially capturing over 50% of the market share. The major challenge is the 800 GW TOPCon capacity, with BC’s growth relying on both corporate and governmental efforts. On the other hand, TOPCon’s progress has significantly slowed, particularly due to challenges in dual-side passivation. In contrast, BC’s rear-side optimization offers superior results, indirectly spurred by the limitations of TOPCon. Shen says that BC’s trajectory suggests it could achieve a 50% market share in as little as 3 to 5 years, solidifying its role as the next major technology in photovoltaics.
The dialogue emphasized the importance of building a robust ecosystem for widespread of BC technology. Chen highlighted the longstanding collaboration between AIKO and LONGi while acknowledging different product strategies for each. He stressed that BC technology is a shared asset of the photovoltaic (PV) industry, advocating for open development and collective progress. However, respecting intellectual property (IP) is equally important, given the substantial early R&D investments by pioneers like AIKO and LONGi. Chen called for fair and transparent sharing of these costs and proposed establishing industry-wide guidelines to protect IP, while fostering innovation and shared benefits.
Zhong reiterated the importance of collaboration, citing LONGi’s extensive experience in ecosystem development. He emphasized that most of LONGi’s breakthroughs, particularly in monocrystalline technology, were achieved through collaboration. He emphasized the need for partnerships across the value chain, including upstream suppliers, downstream manufacturers, material suppliers and end-users, particularly as BC technology finds applications in diverse consumer-oriented products.
Both leaders stressed the need for a balanced approach that fosters innovation while respecting IP rights. They acknowledged the progress made in China's IP environment and expressed their commitment to responsible collaboration. They advocated for an industry culture that encourages cooperation, respects IP, and promotes the sustainable development of BC technology.
The panelists shared a unified vision of a zero-carbon future powered by affordable and accessible solar energy.
Wenzhong highlighted the transformative potential of solar power, emphasizing its role as the foundation for a zero-carbon society. He noted that solar energy has become the world’s cheapest energy source, now grid-competitive and often the most affordable option globally. This cost advantage makes solar power a cornerstone for sustainability initiatives, enabling hydrogen production to become economically viable. Hydrogen, in turn, can be used to produce renewable fuels like ammonia and methanol, supporting long-term sustainability over the next 20 to 30 years. Wenzhong underscored that integrating solar with storage and microgrids creates a robust energy framework to address both national and global sustainability goals.
Zhong Baoshen detailed LONGi's multi-stage roadmap to a zero-carbon world. This roadmap begins with expanding solar and wind energy while utilizing flexible resources to support the current energy system. As renewable sources grow, the focus shifts to developing robust energy storage solutions, such as pumped hydro and electrochemical storage, to address grid integration and intermittency challenges. The next stage involves tackling the remaining energy demand by utilizing green hydrogen in sectors like transportation and steelmaking, further reducing reliance on fossil fuels. Ultimately, LONGi envisions a "negative-carbon earth" where abundant, inexpensive solar energy enables large-scale seawater desalination, which could greenify arid regions and create carbon-absorbing oases.
Chen Gang emphasized the need for integrated zero-carbon energy systems, combining primary sources like solar with secondary sources like hydrogen to ensure affordability and energy security. There is a dire need to address bottlenecks in infrastructure, including microgrids and distribution networks, to unlock the full potential of solar energy. He attributed the current oversupply of photovoltaic modules to lagging infrastructure development rather than a lack of demand, highlighting the need for investment in smart grids and distribution networks.
In her closing remarks, moderator Lü Fang connected the dialogue to a recent International Energy Agency initiative themed "PV everywhere," which promotes the ubiquitous integration of solar energy. This aligns with LONGi's evolving concept of "solar for solar," initially focused on powering solar manufacturing with solar energy, and now expanded to "solar for all," advocating for widespread solar adoption across all sectors. She reflected on how the discussion highlighted this transition, where solar energy will evolve from a supplemental source to a primary source, and eventually become the dominant force driving the global energy transition.
.png?w=50&fm=png){kind=logo}