A research group led by Chinese polysilicon and solar module manufacturer Tongwei has developed a tunnel oxide passivated contact (TOPCon) solar cell featuring an emitter with higher sheet resistance in a bid to reduce recombination losses, improve surface passivation and increase power conversion efficiency.

“In our work, a non-destructive photoresist-based etching process was used to form a selective emitter structure for TOPCon solar cells,” corresponding author Xiajie Meng told pv magazine. “The structure features a sheet resistance as high as 1,600 Ω/sq – to the best of our knowledge, the highest reported for TOPCon to date. This successful implementation confirms that TOPCon remains highly competitive for commercial applications.”

The researchers explained that conventional TOPCon cells face a trade-off between low contact resistance and reduced carrier recombination in the boron-doped emitter. The proposed architecture addresses this limitation by combining heavily boron-doped regions beneath the metal contacts with lightly doped regions between the contacts.

The scientists used a range of characterization techniques to investigate the structural, electrical and passivation properties of the proposed cell architecture, with the aim of identifying optimal design conditions that balance surface passivation, lateral charge transport and metal shading losses.

They used scanning electron microscopy and 3D laser microscopy to examine etching depth and surface morphology, while four-point probe measurements determined the sheet resistance of the lightly and heavily boron-doped emitter regions. They also evaluated contact resistivity using the transmission line method and characterized doping profiles and junction depths through electrochemical capacitance-voltage measurements.

The team assessed minority carrier lifetime and emitter recombination using quasi-steady-state photoconductance measurements.

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