Co-annealing of PECVD boron emitters and poly-Si passivating contacts for leaner TOPCon solar cell fabrication

Abstract

This study investigates the feasibility of a single-step annealing process for tunnel oxide passivating contact (TOPCon) solar cell fabrication to replace the conventional two-step approach. We present a novel method using a single thermal treatment to simultaneously form the boron emitter at the front and poly-Si-based passivating contact at the rear of the device. Both are based on layers deposited by plasma-enhanced chemical vapor deposition (PECVD). First, we tailor the boron emitter profile. We achieved boron emitter profiles with surface concentrations ranging from $3\times 10^{19}\text{to}1\times 10^{20}{\text{cm}}^{-3}$ and depths between 100 and 600 nm by adjusting the deposition parameters and annealing conditions. Secondly, we show that $n$-type poly-Si layers are suitable for co-annealing when an additional N₂O plasma treatment is applied to tunnel oxide formed by exposure to UV-O₃. This approach enables the achievement of $i{V}_{oc}$ up to 720 mV and contact resistivity $\le 100m\Omega {cm}^2$. Finally, we demonstrate the viability of the co-annealing process with a proof-of-concept solar cell, which shows a promising power conversion efficiency of 21%.