ИСТИНА

The objective of this work was to develop a bifacial version of (p+nn+)Cz-Si solar cell with aluminiumalloyed p+ emitter, at that, based on the Laminated Grid Cell (LGCell) design, i.e. with the current collecting system made of copper wire attached to transparent conducting oxide layer, which acts as a transparent electrode as well as an antireflection and passivation coating; at that Indium-Fluorine-Oxide (IFO) film is used on n+-Si diffused layer and Indium-Tin-Oxide (ITO) film – on p+-Si layer. In reference monofacial version, based on IFO/(n+np+)Cz-Si/Al structure with a full-area non-passivated Al-p+ side, the wires make contact to screen-printed aluminium paste. For the reference monofacial cell, we demonstrate performance with rear efficiency of 17.3%. To obtain bifacial solar cells, aluminium paste matrix was removed and p+ layer was thinned by etch-back from 13 Ω/□ to 18 Ω/□ (cell #A18), 26 Ω/□ (cell #A26) and 38 Ω/□ (cell #A38). It was revealed that the rear efficiency of bifacial ITO/(p+nn+)Cz-Si/IFO solar cells is considerably lower than of the reference monofacial cell: 14.5% (#A18), 14.7% (#A26) and 14.8% (#A38). This great drop in efficiency is caused mainly by the reduction of the photocurrent (from 33.4 mA/cm2 down to 29 mA/cm2 for cell #A18). However, thinning of the emitter slightly restored the photocurrent (up to 29.8 mA/cm2 for cell #A38) and, correspondingly, the efficiency. Front efficiency of bifacial cells considerably increased with the p+ emitter thinning from 11.4% (#A18) up to 14% (#A38) mainly due to the increase in photocurrent from 22.8 mA/cm2 up to 28.5 mA/cm2 (+25%). It was also revealed that an additional annealing of the (p+nn+)Cz-Si structure after aluminium matrix removal considerably improves the rear efficiency of the bifacial cell up to 16.5% mainly due to the restore of the photocurrent (up to 34.5 mA/cm2), which is even higher as compared with the reference cell.