A 22.3% Efficient p‐Type Back Junction Solar Cell with an Al‐Printed Front‐Side Grid and a Passivating n⁺‐Type Polysilicon on Oxide Contact at the Rear Side

Abstract

The fabrication of a silicon solar cell on 6 in. pseudo‐square p‐type Czochralski grown silicon wafers featuring poly‐Si‐based passivating contacts for electrons at the cell rear side and screen‐printed aluminum fingers at the front side is demonstrated. The undiffused front surface is passivated with an Al2O3/SiNx stack, and the rear surface is covered with a thin oxide/n+‐poly‐Si/Al2O3/SiNx layer system, contacted by screen‐printed silver fingers. A loss analysis shows that the recombination losses at the metal contacts on both cell sides dominate the total energy losses. A voltage of 700 mV as the highest open‐circuit voltage from a batch of seven cells is achieved, and the best cell efficiency is 22.3%, independently confirmed.

716 mV Open‐Circuit Voltage with Fully Screen‐Printed p‐Type Back Junction Solar Cells Featuring an Aluminum Front Grid and a Passivating Polysilicon on Oxide Contact at the Rear Side

“…Second, we improved the passivation quality of the POLO contacts from previously 9 to now 3.5 fA cm À2 as determined on test structures. When incorporating both these changes in our simulation model reported in our previous work, [14] then the simulation predicts a V oc improvement of 5.3 mV, indicating that the V oc improvement of 22 mV reported here is mainly due to less damage to the POLO contacts underneath the screen-printed metal contacts. The median J sc values differ by 0.1 mA cm À2 from the value of the previous cell batch, but the difference is within the uncertainty range.…”

“…The impact on cell performance is investigated by fabricating POLO back junction (BJ) solar cells with p-type M2-sized Czochralski-grown silicon wafers. [12][13][14] As shown in Figure 1, the POLO BJ cells have screen-printed aluminum fingers at the front side that form local p þ regions. The undiffused, textured front side is passivated with Al 2 O 3 /SiN x stack.…”

“…The advantage of this cell concept is discussed in our previous work in detail. [14] Figure 2 shows the box plots of measured I-V parameters and contact resistivities as a function of peak firing temperature. The box height spans from the first to the third quartile (also known as interquartile range [IQR]), and the whiskers indicate the maximum and minimum of 1.5 Â IQR beyond the box.…”

“…The numbers next to the boxes give the median values. The red boxes show the I-V parameters and contact resistivities of POLO BJ solar cells fabricated in this work with a 60 nm thick SiN x capping layer at the rear, whereas the green boxes show the results from previously published work [14] with a 40 nm thick SiN x capping layer at the rear. The busbarless solar cells are measured on a reflective chuck using 12 contact bars under AM1.5 G illumination at 25 C. The I-V measurements with LOANA tool from pvtools apply contacting scheme that neglects the resistance of the metal grid.…”

Simulation-based roadmap for the integration of poly-silicon on oxide contacts into screen-printed crystalline silicon solar cells

“…We actually started experimental work in this direction. For POLO BJ, we achieved an independently confirmed efficiency of 22.3 % within a (on our scale) very short development time of 1/2 year 79 , 80 . For POLO IBC, we achieved so far an open-circuit voltage of 711 mV and an efficiency of 22.6% on small area 81 , 82 .…”