Back Contact Solar Cells: From Simple Designs to HIBC

Key takeaways:

• BC architectures continue to diversify, incorporating different wafer types and passivated contact approaches

• Most modern BC designs build on passivated contact concepts, particularly TOPCon-based structures

• LONGi's HIBC architecture combines TOPCon and HJT elements, reaching a certified cell efficiency of 27.81%

It is common knowledge in PV that the distinctive feature of back contact solar cell architecture is that both the polarities – p- and n-type – of the solar cell and the respective contacts are on the rear side. While this is the generic description, there are several variations.

The defining characteristic of all BC cells is the relocation of the p-type (hole-selective) and n-type (electron-selective) regions to the rear side, creating a front surface that is entirely free of metal grid lines. It consists of interdigitated diffused p+ and n- regions on the rear side. This BC structure has evolved from basic interdigitated designs into complex, multi-layered structures that integrate the latest advancements in passivated contacts.

One variation also originate from the base wafer, which can be p- or n-type, but not anymore. Earlier generations of BC technology from LONGi were based on p-type wafers, but the company eventually moved to n-type wafers. Another key variant involves adapting the passivated contact strategy to the back contact design, and most BC structures fall into this group. Initially, early BC designs passivated only one contact polarity, but subsequent developments added passivation for both polarities. Then there is also a choice between contact passivation strategies – TOPCon or HJT. The majority of today’s BC technologies are adaptations of the former. However, Kaneka’s HJT-based BC structure was the world record holder for about 5 years between 2017 and 2022.

The most interesting evolution of the BC structure is the Hybrid Interdigitated Back Contact (HIBC) cell developed by LONGi. This structure represents a strategic fusion of high-temperature processed polysilicon (TOPCon-like) and low temperature- processed amorphous silicon (HJT-like) technologies. The HIBC cell uses a high-temperature regime for the n-type regions and employs a low temperature HJT processing for the p-type regions, allowing each polarity to be optimized independently for maximum passivation quality.

In April 2025, LONGi’s HIBC technology achieved a world-record efficiency of 27.81%, as certified by the Institute for Solar Energy Research in Hamelin (ISFH). This world-record cell is built on industrial grade gallium-doped silicon wafers and achieves a record fill factor of 87.55%. The HIBC architecture effectively solves the poor vertical conductivity typical of traditional amorphous silicon layers by utilizing laser-induced localized crystallization at the pyramid tips. This innovative approach drastically reduces vertical contact resistivity while maintaining low lateral leakage current in the polarity-overlapped regions.

The text is an edited excerpt from TaiyangNews’ report on Cell & Module Technology Trends 2026, which can be downloaded for free here.