New progress has been made in the field of high-efficiency crystalline silicon solar cell technology

Wan Qing's research group at the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, proposed a cross self-alignment process and developed a high-efficiency crystalline silicon solar cell using ordinary screen printing equipment. After high-temperature phosphorus diffusion, the conventional crystalline silicon cell process has a layer of phosphorus-silicon glass with a high concentration of phosphorus on the surface of the cell. Through laser patterning annealing with a wavelength of 532nm, the phosphorus in the phosphorus-silicon glass is further diffused into silicon, thereby forming a selectively heavily doped area on the surface of the cell. When screen printing silver paste, the fine grid lines are made to cross the laser heavily doped lines at 90 degrees, cleverly realizing the self-alignment preparation process.

In the application of crystalline silicon solar cells, the characteristics of the emitter can greatly affect the performance of the cell. The contact resistance of the cell can be reduced by increasing the doping concentration of the emitter, but too high a doping concentration will increase the recombination rate of photogenerated carriers in the emitter. The selective emitter cell structure effectively solves this contradiction. In this cell structure, a higher concentration of doping is used under the metal grid line. At the same time, the emitter between the grid lines maintains a lower doping concentration, thereby reducing the series resistance of the cell while ensuring a good blue light response. However, this cell structure requires a strict alignment process to achieve electrical contact between the metal grid line and the selective emitter.

The battery performance test shows that the best fill factor of a standard monocrystalline silicon cell (125mm×125mm) with an emitter square resistance of 75 ohms/square is increased from ~65% before laser doping to ~79% after laser doping; the best cell photoelectric conversion efficiency is increased from ~14.4% before laser doping to ~17.7% after laser doping. The improvement in cell performance is mainly due to the improvement in cell contact performance.

The research results provide a new way to explore high-efficiency crystalline silicon cells. The related paper was published in Solar Energy Materials and Solar Cells (95 (2011) 3347-3351).