With the use of low-silver paste in HJT cell metallization, Risen aims to reduce its current silver consumption to below 6 mg/W, which is lower than TOPCon’s 9 mg/W and PERC’s 6.6 mg/W
The company has incorporated a thin TCO layer on both the front and rear surfaces which offers high conductivity, light transmittance, and anti-reflective properties
Risen recently launched the Hyper-ion Pro series 730W+ HJT module, to be mass-produced by Q1 2025
Heterojunction technology (HJT), one of the mainstream n-type cell technologies, demands a balancing act between production cost, efficiency, and reliability to stay competitive with peers like TOPCon. Several tier-1 HJT product makers have addressed these demands in the last few years by navigating multiple technological pathways.
Jiajun Ye, Senior Product Manager at Risen Energy, presented the technological advancements from last year integrated into the latest HJT module at TaiyangNews' annual flagship conference – High-Efficiency Solar Technologies 2024 (see Risen Energy's presentation here).
Risen Energy, a vertically integrated photovoltaic company headquartered in Zhejiang, China, boasts a production capacity of up to 40 GW for cells and 48 GW for modules annually. Of this, the company has dedicated up to 19 GW of cell capacity and 21 GW of module capacity to the HJT stream. Beginning its R&D on HJT cell technology in 2018, the company launched a 210 mm wafer-based Hyper-ion series HJT module in 2022. The technology has since undergone multiple advancements, including the release of the 741.45 W HJT module in 2023, and the latest 767.38 W Hyper-ion Pro series.
Ye began his presentation with a brief overview of the HJT technology advancements integrated into mass production over the past few years. The company has successfully addressed the challenge of balancing the high conductivity of the emitter with optimizing metallization costs by adopting several innovations, including low-silver metallization paste, silver-coated copper paste with low silver content, and copper plating. By continuing to use low-silver paste, which remains the market’s mainstream, Ye says Risen can further reduce its current silver consumption to below 6 mg/W, which is lower than TOPCon’s 9 mg/W and PERC’s 6.6 mg/W. This reduction in silver usage could lead to a reduction in HJT metallization costs to up to 4.4 RMB cents/W in H2 2024, compared to the current 4.8 RMB cents/W in H1 2024. Additionally, Risen has incorporated multiple technological improvements, such as 0BB technology to reduce shading, wafer thickness reduction to as low as 90 µm, and the patented low-temperature stress-free interconnection technology known as Hyper-link.
Following the overview of major technological improvements in mass production, Ye highlighted key advancements for 2024. He explained that the lower conductivity of the cell’s emitter region, which is affected by the amorphous silicon (a-Si) layers on both sides, cannot alone ensure the cell's high efficiency, thus requiring an electrical solution. Risen has addressed this challenge with a thin Transparent Conductive Oxide (TCO) layer on both the front and rear surfaces, offering high conductivity, light transmittance, and anti-reflective properties. To deposit this thin layer, the company employs field deposition processes like target material sputtering, where high-speed ion beams bombard the target material, causing atoms to sputter and deposit onto a substrate, forming a thin film. The key to achieving higher cell efficiency lies in 3 critical properties of the TCO layer: low resistivity, high transmittance, and the ability for low-temperature growth. Risen has opted to increase carrier mobility rather than carrier concentration to achieve low resistivity at the cell surface. The carrier concentration route leads to higher light absorption and reduced transmittance, leading to lower cell efficiency.
Moreover, the company has replaced traditional screen printing technology with stencil mesh (knotless) printing technology. This method features a fully open mesh, higher paste transmittance, and a longer printing lifespan in the metallization process. The new technology reduces finger width to less than 25 µm, minimizing shading and increasing the area available for light absorption. It also enhances printing quality, achieving an aspect ratio of up to 46%, compared to just 28% with conventional mesh technology. Additionally, Risen has incorporated UV-down conversion film, which utilizes the Stokes shift principle to convert high-frequency, high-energy UV light into low-frequency visible blue light. This results in an additional power gain of 10 W compared to conventional UV cut-off films.
The technological advancements described above have culminated in Risen’s upcoming Hyper-ion Pro series 730 Wp+ HJT module, which is expected to enter mass production in Q1 2025. This module, featuring 132 HJT cells, will deliver a power output of up to 740 Wp and an efficiency of up to 23.8%.