21.2%-efficient fineline-printed PERC solar cell with 5 busbar front grid

Abstract

We evaluate industrial‐type PERC solar cells applying a 5 busbar front grid and fineline‐printed Ag fingers. We obtain finger widths down to 46 µm when using a stencil with 40 µm opening for the finger print, whereas the busbar is printed in a separate printing step with a different Ag paste (dual print). This compares to finger widths of 62 µm to 66 µm when applying print‐on‐print. The 5 busbar front grid with the best dual print process reduces the shadowing loss of the front grid to 4.0% compared to 5.8% for a conventional 3 busbar front grid printed with print‐on‐print. The 1.8% reduction in shadowing loss results in equal parts from the reduced finger width with dual print as well as from a reduced total busbar width of the 5 busbar design. The resulting PERC solar cells with 5 busbars demonstrate independently confirmed conversion efficiencies of 21.2% compared to 20.6% efficiency of the 3 busbar PERC solar cell. The increased conversion efficiency is primarily due to an increased short‐circuit current resulting from the reduced shadowing loss. To our knowledge, 21.2% conversion efficiency is the highest value reported so far for industry typical silicon solar cells with printed metal front and rear contacts. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

A Systematic Loss Analysis Method for Rear-Passivated Silicon Solar Cells

“…This difference alone contributes to 3% × 46.37 mA/cm 2 = 1.39 mA/cm 2 in lost current density. Notwithstanding the metal shading, in the nonshaded areas, the current density is reported to be 41.3 mA/cm 2 for the state-of-the-art LBSF cell [19], which is practically identical to the nonshaded area current density calculated for the cell in this study. In reality, it is difficult to quantify very fine differences in cell J sc , especially for two cells that were measured under different solar simulators.…”

“…The current record LBSF cell, for example, has a current density J sc of 39.8 mA/cm 2 [19]. One obvious difference is in the front grid metallization fraction, being 4% for the state of the art cell compared with 7% for the cell of this study.…”

“…In comparison, the state-of-the-art LBSF cell has consistently IQE ∼ 96% at 1000 nm [19], [21]- [23], which implies roughly 0.2 mA/cm 2 higher J sc from reduction in base collection loss according to PC1D. As a lower bound, using bulk diffusion length and rear surface velocities reported by Gatz et al for a Ga-doped light-stabilized LBSF cell [23], the simulation shows that there is at least a difference of 0.1 mA/cm 2 .…”

“…5 gives a comprehensive overview of the recombination loss mechanisms and offers a basis of comparison to state-of-the-art LBSF solar cells. The plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiN x ) passivated emitter is excellent, having a J 0e of less than 100 fA/cm 2 [19], [20]. On the other hand, the combination of bulk recombination and rear recombination at the passivated rear, consisting of a PECVD aluminum oxide and silicon nitride (AlO x /SiN x ) stack, contributes about 117 fA/cm 2 , which is many times higher than the J 01,base,pass reported for LBSF c-Si cells with high V oc and rear passivation surface recombination velocity of less than 10 cm/s [21]- [23].…”

21.0%-efficient screen-printed n-PERT back-junction silicon solar cell with plasma-deposited boron diffusion source

“…On the front side, a PECVD SiN y layer acts as passivation and as anti-reflecting coating (ARC). After laser contact opening on the rear side, the front side metallization is performed by Ag-screen printing applying a 5 busbar layout and a dual print process as described in [16]. Full-area Al-screenprinting on the rear side and co-firing finalize the cell as sketched in Fig.…”