According to the Chinese Academy of Sciences, a team from the Ningbo Institute of Materials Technology and Engineering (NIMTE) has fabricated a TOPCon solar cell on an industrial standard M10-size silicon wafer, achieving a conversion efficiency of 26.66%. This was accomplished through a novel strategy of coordinated electrical optimization on both sides of the cell. The cell also set new industrial records with an open-circuit voltage of 744.6 mV and a fill factor of 85.57%, providing a new pathway for the industrial upgrading of high-efficiency TOPCon technology.
The key performance indicators for this cell include: a certified conversion efficiency of 26.66%, an open-circuit voltage (Voc) of 744.6 mV, a fill factor (FF) of 85.57%, and an improved bifaciality rate of 88.3%. Its product of Voc × FF reached 93.8% of the theoretical limit. The research findings have been published in the international journal Nature Energy.
Regarding the optimization of the cell’s front-side structure, the research team achieved two significant advances. First, they developed a high sheet resistance boron emitter of 430 Ω/sq, achieving a low doping concentration and a shallow junction design. This increased the minority carrier lifetime from 0.70 ms to 1.12 ms and reduced the saturation current density from approximately 9 fA/cm² to about 5 fA/cm², significantly decreasing carrier recombination losses. Second, through refined gridline design, they narrowed the gridline spacing from the conventional 1120 μm to 825 μm and reduced the line width from 20 μm to 10 μm. This effectively decreased the lateral transport resistance of carriers, improved current collection efficiency, and reduced both shading losses and silver paste consumption.
On the cell’s rear side, the team constructed an innovative double-layer structure consisting of a tunneling oxide layer and a polysilicon stack. The inner layer, approximately 40 nm thick and lightly doped, is responsible for interface passivation and acts as a barrier against silver diffusion. The outer layer, about 60 nm thick and heavily doped, serves as the conductive layer. This structure effectively blocks the diffusion of silver atoms into the silicon substrate, preventing the formation of carrier recombination centers. Furthermore, by employing a laser modification process combined with wet chemical etching, they locally thinned the polysilicon layer in the non-metalized areas on the rear side. This resulted in approximately 70% of the rear surface retaining only the inner polysilicon layer, which reduced parasitic absorption losses and enhanced the cell’s bifacial power generation capability.
Through this coordinated and refined electrical optimization of both the front and rear sides, the research successfully reconciled “stronger passivation” with “lower transport/metallization losses” in industrial-grade TOPCon cells. This provides a clear and manufacturable engineering pathway for the development of high-efficiency industrial TOPCon technology. The research work was supported by the National Natural Science Foundation of China.
