JinkoSolar Unveils 28% Efficient Back-Contact TOPCon Cell With Amorphous Silicon Passivation

JinkoSolar has unveiled its new TAC technology, featuring back-contact TOPCon cells with amorphous silicon passivation, at Global Tech Day in Shanghai on Oct. 17. The company says the design achieves a peak cell efficiency of 28%.

The announcement highlights JinkoSolar’s continued push into advanced cell architectures. While the 28% figure represents a specific test result, it underscores the industry’s ongoing focus on maximizing conversion rates.

This development adds to the broader trend of manufacturers exploring complex passivation layers to reduce recombination losses. As with other recent disclosures, the reported efficiency reflects preliminary data from the company’s internal testing.

Hybrid Contact Architecture

JinkoSolar’s TAC design merges two distinct cell technologies into a single structure. It pairs the electron contacts characteristic of TOPCon cells with the hole contacts found in heterojunction technology (HJT). This hybrid approach sits on an n-type crystalline silicon wafer, utilizing a rear-electrode layout where all electrical connections are placed on the back side of the cell. By moving the metal contacts away from the front, the design removes the need for front-side metallization.

This structural choice directly addresses optical shading, a common loss factor in conventional solar cells where metal fingers block sunlight from reaching the active semiconductor material. Reducing these shaded areas allows more photons to interact with the silicon, potentially improving energy capture. In the broader context of photovoltaic development, back-contact architectures are often pursued to maximize the active area of the cell. While various manufacturers explore different configurations to minimize recombination and shading, this specific combination of TOPCon and HJT contact schemes represents a distinct path within the back-contact family. The integration of these two technologies aims to leverage the strengths of each contact type while eliminating the visual and efficiency penalties associated with front-side metalization.

Material Process Details

The specific materials used in each contact region are engineered to manage charge carrier transport and surface recombination effectively.

• Electron-collecting region utilizes a silicon oxide tunneling layer with a thickness between 1 nm and 2 nm.
• Hole-collecting region employs both intrinsic and doped hydrogenated amorphous silicon.
• The amorphous silicon passivation step is performed at temperatures below 200 C.

The electron side relies on an ultra-thin silicon oxide layer, which is critical for allowing electrons to tunnel through while blocking holes, thereby preventing recombination at the interface. This atomic-scale precision is a hallmark of advanced passivated emitter and rear cell designs. On the opposite side, the hole-collecting region uses hydrogenated amorphous silicon. This material choice is notable because amorphous silicon is often associated with thin-film photovoltaics, but here it serves purely as a passivation layer to stabilize the surface and reduce defects.

The thermal budget for this process is a key differentiator. Because the amorphous silicon passivation occurs below 200 C, the process is compatible with standard crystalline silicon manufacturing lines that might otherwise be limited by high-temperature steps. Lower-temperature processes can reduce energy consumption and thermal stress on the wafer, which is significant for large-scale production where maintaining cell integrity across millions of units is a primary concern. This thermal compatibility allows the hybrid architecture to integrate more easily into existing fabrication workflows without requiring entirely new high-temperature furnaces.

Performance Metrics

JinkoSolar reports that production cells based on this architecture achieve efficiencies exceeding 27%, a figure that distinguishes the technology from the peak 28% laboratory result announced earlier. This gap highlights the typical challenge manufacturers face when scaling advanced cell designs from controlled lab environments to high-volume manufacturing lines, where process variability and yield constraints often temper initial performance gains. For investors and supply chain partners, a production efficiency above 27% suggests the design is nearing commercial viability, as it exceeds the performance levels of many current mainstream technologies.

To support these numbers, the manufacturing process relies on high-precision laser patterning and dielectric isolation to define cell structures with minimal defect density. The company identifies recombination losses as a primary target for reduction, employing a Global Passivation Process designed to stabilize surfaces across the entire cell area. A Multi-Dimensional Charge Passivation technique specifically addresses recombination at cut-cell edges, areas that often suffer from higher defect densities due to mechanical stress during wafer slicing.

Underlying these architectural improvements are strong material quality metrics. The silicon substrate bulk minority-carrier lifetime exceeds 2 ms, a duration that allows charge carriers to travel further before recombining, thereby increasing the likelihood of collection. Correspondingly, the bulk recombination current density remains below 5 fA/cm², indicating that the intrinsic material contributes minimally to energy loss. These parameters demonstrate that the efficiency gains stem from effective surface and edge management rather than solely from optical improvements, ensuring that the electrical potential of the high-quality silicon is fully realized in the final module.

What to watch

JinkoSolar’s roadmap points toward refining the electrical connections that currently define this hybrid structure. Future development efforts will focus on low-temperature metallization, a shift that aligns with the sub-200 C amorphous silicon passivation already integrated into the process. By keeping metalization steps cool, manufacturers can avoid thermal degradation of the delicate tunneling layers, potentially preserving the high minority-carrier lifetimes observed in the silicon substrate. The company plans to introduce copper-containing contact materials. Replacing traditional silver with copper offers a distinct supply chain advantage, as copper is far more abundant and less volatile in price than precious metals. For module manufacturers, this substitution could significantly reduce bill-of-materials costs without sacrificing the conductivity required for high-efficiency back-contact designs.

Beyond standalone silicon cells, this architecture is being evaluated as a bottom-cell platform for perovskite-silicon tandem devices. Tandem cells stack a top perovskite layer, which absorbs visible light, over a silicon bottom cell that captures near-infrared wavelengths. The back-contact layout is particularly well-suited for this configuration because it frees the front surface of metal fingers, allowing the perovskite layer to receive unobstructed light. As the industry moves toward these stacked technologies, the stability and passivation quality of the silicon base become critical. Success in this area will determine whether the current efficiency gains can be sustained when the cell is integrated into a more complex, multi-junction stack.