Both-Sided TOPCon Solar Cells – Towards a Lean Process Flow for Silicon Bottom Solar Cells

Abstract

Silicon solar cells with both-side full-area passivating hole and electron contacts are viable candidates for application as bottom cells in tandem architectures. In this contribution, cells with poly-Si based contacts at both sides are investigated as a potential upgrade to the emerging i-TOPCon single junction devices featuring a passivating contact (poly-Si(n)/SiO_x) only at the rear side and an alternative to the SHJ technology featuring a-Si based full-area passivating hole and electron contacts. We show that a higher thermal budget is needed to mediate between poly-Si(p)/SiO_x hole and poly-Si(n)/SiO_x electron contact when the same thermal interfacial SiO_x is applied. This is addressed by using a PECVD oxide that is adapted to the needs of the hole and/or the electron contact. We present a proof-of-concept poly-Si(n)/SiO_x/c-Si/SiO_x/poly-Si(n) device with emphasis on a lean process flow. An all-PECVD process sequence for the hole contact, i.e., plasma oxides+i/p-a-Si deposited at 200°C in the same chamber was applied. With co-annealing of the contacts, no additional hydrogenation, and no edge insulation step, we observe no shunting and obtain efficiencies of up to 20.8% for M2 size cells, so far.