A simpler pathway for back-contact silicon solar cells

In November 2025, Lizhi Sun (UNSW) received the Best Student Oral Presentation Award at PVSEC-36 in Bangkok for presenting groundbreaking work on cost-effective self-doping in back-contact silicon solar cells. The work has just been published in Solar Energy Materials and Solar Cells.

Back-contact silicon solar cells are widely recognised for their efficiency advantages, enabled by the removal of front-side metal shading and improved carrier collection. However, despite their technical appeal, large-scale adoption has been constrained by their manufacturing process complexity and cost, particularly around forming n-type regions on the rear side of the cell.

Conventional back-contact architectures typically rely on high-temperature phosphorus diffusion and silver-based metallisation, combined with precise patterning steps. These processes add cost, increase equipment requirements, and complicate integration into existing industrial production lines.

The study, led by Lizhi Sun, Dr Ning Song and colleagues including Professor Martin Green at the University of New South Wales, in collaboration with Toyo Aluminium KK, presents a compelling solution to this long-standing bottleneck. The published paper, "In-situ n-type doping by screen-printed aluminum paste for back contact silicon solar cells", demonstrates for the first time a modified, screen-printable aluminium paste capable of forming n-type regions directly during contact firing.

The ACAP supported team, including (l-r) Yuhao Cheng, Dr Ning Song and Lizhi Sun (right) developed an aluminium paste that simplifies and reduces the cost of back-contact silicon solar cell manufacturing.

The approach enables so-called in-situ self-doping: on p-type silicon, the aluminium paste forms an n+ emitter, while on n-type silicon it creates an n+ back surface field – all in a single firing step. Crucially, this eliminates the need for silver contacts and separate phosphorus diffusion, while remaining fully compatible with standard industrial screen-printing processes.

“This work is important because it addresses a long-standing practical bottleneck in back-contact silicon solar cell manufacturing,” said Dr Ning Song.

“By demonstrating a simpler and more manufacturable pathway, we show how back-contact designs can move closer to large-scale, cost-effective deployment.”

The schematic of potential application in back contact solar cells for the Al paste developed by the UNSW team.

Beyond the immediate technical achievement, the study introduces the concept of “doping dominance” to explain how competing p-type and n-type reactions can be controlled through paste chemistry and thermal processing – offering a new framework for contact and junction design.

The team hopes the work will stimulate further development of Ag-free, lower-cost back-contact solar cells, and encourage closer collaboration between materials researchers and industry. Supported by ARENA, with long-term backing from ACAP, the research highlights how rethinking metallisation strategies can reduce material use, simplify manufacturing, and support the long-term sustainability of silicon photovoltaics.