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Co-Diffused Back-Contact Back-Junction Silicon Solar Cells without Gap Regions

Figure 1

Figure 1
In this figure, the process effort for manufacturing a BC-BJ doping structure is compared for successive diffusion and co-diffusion. With the numbering, the number of process-steps for every mentioned process-type is depicted. Successive diffusion means the diffusion from gaseous sources with local SiOx-diffusion barriers. Co-diffusion means the simultaneous diffusion from pre-patterned doped silicate glasses as carried out in this study. By manufacturing a co-diffused BC-BJ cell without gap shallowly diffused (00-cell) instead of a successively diffused cell with gap shallowly diffused (10-cell), 12 process steps can be saved. This effort analysis considers the processes needed for just the assembly of the BC-BJ doping structure. The bordered box on the bottom right gives an alternative designation for the several cell-types.

Figure 2

Figure 2
Figure shows the process sequences for the fabrication of the BC-BJ doping-structure without gap (00-cell) and with gap (10-cell) shallowly diffused. The simultaneous doping of silicon to Formula$n^{+}$-Si (FSF and BSF) and Formula$p^{+}$-Si (Emitter) is performed by pre-patterned solid diffusion sources. For the fabrication of the cell with gap, an additional deposition and patterning step is necessary.

Figure 3

Figure 3
ECV-measured charge carrier concentration Formula$n$Formula$(x)$ and Formula$p$Formula$(x)$ of the BSF, FSF, and emitter shallowly diffused (x0-cell). The silicon surface of the cell rear side corresponds to the position Formula$x$ = 0 μm.

Figure 4

Figure 4
ECV-measured charge carrier concentration Formula$n$Formula$(x)$ and Formula$p$Formula$(x)$ of the BSF, FSF, and emitter deeply diffused (x1-cell).

Figure 5

Figure 5
Internal quantum efficiency (IQE) and reflectance (Formula$R)$ as a function of the wavelength Formula$({\lambda})$ for a BC-BJ solar cell with (11-cell) and without gap (01-cell) deeply diffused. Within this comparison, cells with constant cell dimensions were selected. Each cell has a pitch of Formula$x_{\rm pitch}$ = 1.5 mm and a BSF finger width of Formula$x_{\rm BSF}$ = 300 μm. The IQE of both cells is mainly limited by front side and bulk recombination above the BSF regions on the cell rear side. Formula$J_{\rm SC}$ values as measured by I–V measurements under one-sun conditions are depicted as well.

Figure 6

Figure 6
Fill factor (FF) and pseudo fill factor (pFF) of cells with (10-cell) and without gap (01-cell) deeply diffused as a function of the pitch distance Formula$x_{\rm pitch}$. For every cell-type and pitch distance four cells were measured. Depicted are the mean values as well as the standard deviation of the single measurements. The difference of the FF and the pFF indicates the FF-losses due to the series resistance Formula$R_{\rm S}$.

Figure 7

Figure 7
Cross-sectional view (SEM) on the metal silicon contact of a BC-BJ solar cell. An evaporated Al–Si alloy is used as the metallization layer. The formation of metal spikes after annealing is clearly visible.