Back-surface grid structure of double-side passivated emitter and rear cell (PERC), double-side PERC and preparation method of double-side PERC

The invention discloses a back-surface grid line structure of a double-side passivated emitter and rear cell (PERC), the double-side PERC and a preparation method of the double-side PERC. The back-surface grid line structure comprises a plurality of aluminum grid lines and a plurality of back electrode main grids, wherein the aluminum grid lines are vertically connected with the back electrode main grids, a plurality of segments of laser lines are arranged below the aluminum lines at intervals, the aluminum grid lines are formed by alternatively connecting a plurality of segments of wide aluminum grid lines and a plurality of segments of narrow aluminum grid lines, the numbers of the wide aluminum grid lines are same as the numbers of the laser lines, the wide aluminum grid lines are usedfor covering the laser lines to achieve local ohmic contact between aluminum and silicon and exporting electrons in a silicon wafer, and the narrow aluminum grid lines are used for collecting the electrodes exported from the