Atmospheric Pressure Dry Etching of Polysilicon Layers for Highly Reverse Bias‐Stable TOPCon Solar Cells

Abstract

Single‐sided etching (SSE) of a‐Si/poly‐Si is typically considered a challenge for realizing a cost‐efficient TOPCon production sequence, as there is a certain degree of unwanted wrap‐around for poly‐Si deposition technologies such as low pressure chemical vapor deposition, plasma‐enhanced chemical vapor deposition, and atmospheric pressure chemical vapor deposition. To date, alkaline or acidic wet‐chemical solutions in either inline or batch configurations are used for this purpose. Herein, an alternative SSE process is proposed using an inline dry etching tool, which applies molecular fluorine as the etching gas under atmospheric pressure conditions. The developed etching process performs complete etching of both as‐deposited amorphous silicon and annealed polycrystalline silicon layers, either intrinsic or doped, and with measured etch rates of >3 μm min−1 at 10% F2 concentration allows etching of a typical layer thickness of 200 nm in just a few seconds. The etching process is also configured to perform excellent edge isolation while maintaining a low wrap‐around etching (d rear < 500 μm) at the opposing‐side. The etching process is successfully transferred to the industrial TOPCon solar cell architecture, yielding high parallel resistances (S shunt,avg. > 1500 kΩ cm2), low reverse current density (J rev,avg < 0.8 mA cm−2) measured at a bias voltage of −12 V, and independently certified conversion efficiencies of up to 23.3%.

High Lifetime Ga‐Doped Cz‐Si for Carrier‐Selective Junction Solar Cells

“…6) Single‐sided gas phase removal of poly‐Si on BBr 3 diffused textured front side. [ 9 ] 7) Wet chemical BSG removal and cleaning. 8) Thermal annealing (800–900 °C).…”

Silicon‐based passivating contacts: The TOPCon route

“…Recently, Kafle et al have demonstrated that dry etching using an inline-plasma tool results in high parallel resistance and excellent device performance. 106 In this article we are focusing on onesided wet-chemical etching since it is successfully used to remove the parasitic emitter on the back side in large-scale production. Regarding a later gentle removal of the poly-Si wrap-around, it is very useful to leave the borosilicate glass (BSG) on the front emitter in this process step.…”

“…Various dry and wet processes are known for single‐sided etching of solar cells. Recently, Kafle et al have demonstrated that dry etching using an inline‐plasma tool results in high parallel resistance and excellent device performance 106 . In this article we are focusing on one‐sided wet‐chemical etching since it is successfully used to remove the parasitic emitter on the back side in large‐scale production.…”

Past, Present, and Future Outlook for Edge Isolation Processes in Highly Efficient Silicon Solar Cell Manufacturing

“…A bifacial TOPCon cell batch with n‐type M2 (156.75 ×156.75 mm 2 ) phosphorous‐doped pseudosquare wafers with a base resistivity of ≈1 Ωcm was processed in cooperation with Fraunhofer ISE following the low pressure chemical vapor deposition in situ poly‐Si route, published by Kafle et al [ 33 ] Deviating from this, the n‐poly‐Si layer deposited on the wafer's front side was removed by dry etching via an atmospheric pressure dry etching (ADE) tool. [ 34 ] Moreover, the wafers got an additional cofiring step before metallization to measure implied V oc . After contact formation in a cofiring step at 800 °C, the wafers were treated with a laser‐enhanced contact formation (LECO) step, to further decrease the series resistance of the contact grids ( R S ).…”