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Longi Develops 27.3 Percent Efficient Heterojunction Back-Contact Solar Cells

Longi has unveiled a 27.3 percent efficient heterojunction back-contact solar cell, utilising laser-enhanced manufacturing that reduces material costs and improves performance, offering a promising solution for scalable, high-efficiency solar technology with lower reliance on rare materials.

November 20, 2024. By EI News Network

Chinese solar manufacturer Longi has introduced a new type of heterojunction back-contact (BC) solar cell, achieving a remarkable 27.3 percent power conversion efficiency.

This innovation comes as part of their effort to streamline solar cell manufacturing while improving efficiency and reducing costs.The new BC solar cell design is based on dense passivating contacts that have significantly lower hydrogen content compared to typical BC cells. This modification helps reduce parasitic light absorption and enhances passivation, resulting in higher efficiency.

The device was created using a laser-enhanced contact optimization process, which the company claims is about one-third more effective than conventional technologies like PERC (Passivated Emitter and Rear Contact) and TOPCon (Tunnel Oxide Passivated Contact).

Longi’s breakthrough is documented in the scientific paper 'Silicon Heterojunction Back-Contact Solar Cells by Laser Patterning,' published in 'Nature'. Chaowei Xue, Director of the Department at Longi Solar, explained that this new design could be applied in all silicon-based photovoltaic (PV) applications. The innovative manufacturing technique involves laser patterning, a process that has previously been associated with lower efficiencies, with conventional laser-patterned BC cells not exceeding 22.5 percent efficiency.

Laser patterning traditionally involves three steps—P1, P2, and P3—each serving a specific function in the creation of the interdigitated n/p polarity. However, this process often results in undesired issues like laser-induced damage to the cells, which affects open-circuit voltage and fill factor. Longi's research team developed a method that minimises these risks. The P1 and P3 steps, which isolate the back contact layers, are done using an overlap mode laser, while the P2 step, which creates an electrical path between adjacent cells, is carried out with a single-shot mode to avoid degradation of the crystalline silicon interface.

In the manufacturing process, Longi’s team used a 243.0 cm² M6 phosphorus-doped n-type Czochralski monocrystalline silicon wafer. They deposited the passivating contacts using plasma-enhanced chemical vapor deposition (PECVD) at a temperature of 240°C. The laser used for patterning was a pulsed green picosecond laser with a spot size of 250 μm.

In addition to achieving the impressive 27.3 percent efficiency for their champion cell, Longi also demonstrated other high-performing devices. One version, with reduced indium content, achieved 26.5 percent efficiency, while a screen-printed low-temperature copper (Cu) paste metallised device reached an efficiency of 26.2 percent. Notably, Longi’s manufacturing technique reduces the reliance on rare indium and precious silver, which are critical components in other high-efficiency solar cells such as PERC and TOPCon. This decoupling of heterojunction technology from expensive materials presents a promising path for more cost-effective, scalable solar cell production in the future.

This breakthrough in solar technology has the potential to push the boundaries of solar cell performance while also addressing material scarcity issues, marking a significant step forward in the global push for renewable energy solutions.

Tags:

Power R&D

Chinese solar manufacturer

LONGi Solar

Silicon heterojunction

Chaowei Xue Director

Plasma enhanced chemical vapor deposition

PECVD

PERC

TopCon

crystalline silicon interface