Large-area bifacial n-TOPCon solar cells with in situ phosphorus-doped LPCVD poly-Si passivating contacts

The potential of passivating contacts incorporating in situ phosphorus (P)-doped polycrystalline silicon (poly-Si) films grown by low pressure chemical vapor deposition (LPCVD) is demonstrated in this work by integrating these layers at the rear side of large-area (241.3 cm(2)) bifacial n-type Tunnel Oxide Passivated Contact (nTOPCon) solar cells with diffused front emitter and screen-printed contacts. In situ doped poly-Si films are studied as their use could simplify the production of industrial n-TOPCon solar cells compared to the common approach relying on ex situ doping of intrinsic LPCVD poly-Si films. The developed poly-Si passivating contacts exhibited excellent characteristics with low recombination current densities in passivated and screen-printing metallized regions down to 2.3 fA/cm(2) and 65.8 fA/cm(2), respectively, and a low contact resistivity of 2.0 m Omega.cm(2). For reaching the best passivating contact characteristics and high solar cell efficiencies, a poly-Si film thickness of 150-200 nm was found to be optimal while a polished rear surface morphology was found to be beneficial. The best solar cell reached a certified power conversion efficiency of 23.01% along with a high open circuit voltage of 691.7 mV, enabled by the passivating contacts with the in situ doped poly-Si films. 1-cell glass-glass laminates were also fabricated with the developed solar cells, which showed no loss in their power output both upon 400 thermal cycles and after 1000 h of damp heat testing. Lastly, a roadmap is presented, indicating strategies to achieve efficiencies up to 25.5% with n-TOPCon solar cells incorporating the in situ P-doped LPCVD poly-Si films. The authors would like to acknowledge Sukhvinder Singh from Imec and Rajiv Sharma from KU Leuven for the valuable discussions and their help with the sample fabrication. This work was supported by the European Union’s Horizon2020 Programme for research, technological development, and demonstration [grant number 857793]; and by the Kuwait Foundation for the Advancement of Sciences [grant number CN18-15 EE-01].