TOPCon vs PERC: A Battle of Solar Cell Technologies

Recent research conducted by Germany’s Fraunhofer ISE suggests that TOPCon solar cells are well on their way to fully competing with PERC solar products. However, for the TOPCon concept to gain a larger market share, efficiency improvements are necessary due to higher production costs compared to PERC technology. To address this challenge, a recent study outlines a series of cost-driven strategies aimed at advancing TOPCon pv modules.

TOPCon bifacial solar module

A TOPCon bifacial solar module by FOTOVO

A team of researchers from Germany’s Fraunhofer Institute for Solar Energy Systems ISE has put forth a set of cost-driven strategies to accelerate the industrial development of tunnel oxide passivated contacts (TOPCon) solar products.

Bishal Kafle, the corresponding author of the research, emphasized the importance of maintaining a high conversion efficiency in mass production to compete with state-of-the-art PERC solar cells in terms of system cost and levelized cost of electricity. “Recent advancements in device research have created an increasing gap between the conversion efficiencies of TOPCon and PERC cells. However, there is no standardized process flow established for industrial TOPCon cells,” said Kafle.

In addition to reducing production costs, Kafle highlighted the need for economic viability in TOPCon technology, which requires stable 24/7 production with uptime and utilization rates comparable to current passivated emitter rear contact (PERC) cell manufacturing facilities. He further explained that TOPCon cells on an n-type substrate require silver (Ag) contacts on both sides, and reducing the usage of Ag is an important consideration for the concept in the medium and long term.

The research paper titled “TOPCon – Technology Options for Cost Efficient Industrial Manufacturing,” published in Solar Energy Materials and Solar Cells, outlines that the existing processes and equipment commonly used in PERC cell manufacturing can be easily adapted for TOPCon cell production by incorporating two additional process steps: tunnel oxide formation and the deposition of intrinsic/doped polysilicon.

According to the researchers, optimizing these layers is crucial for designing subsequent cell processing steps to achieve the high open-circuit voltage (VOC) and low series resistance promised by the TOPCon concept. They note that integrating n-type substrates is costlier than p-type counterparts due to the higher costs associated with the boron emitter diffusion process used in PERC cell manufacturing.

The study provides a technical approach to improve the low-pressure chemical vapor deposition (LPCVD) process, which currently serves as the industry standard for TOPCon solar panels. It evaluates alternative techniques based on industrial tool availability, process compatibility, availability of process parameters required for cost of ownership (COO) modeling, lean process flow, and successful demonstration of process functionality.

While LPCVD is considered a valid approach due to its advantages such as good thickness distribution, pin-hole free layers, and in-situ doping capabilities, it has a longer process duration and reduced throughput compared to PERC cell manufacturing, leading to higher production costs. However, the researchers highlight that by combining high-temperature annealing and oxidation of the boron emitter in a single step, the in-situ deposited LPCVD a-Si/poly-Si layers can offer an economically competitive alternative to ex-situ LPCVD a-Si/poly-Si layers.

The ongoing research and development of TOPCon technology aim to address these challenges and improve its efficiency gains and cost competitiveness. With continuous advancements, TOPCon solar cells have the potential to revolutionize the solar industry and provide a viable alternative to PERC technology.